XCP_ReferenceBook_V2.0_ENs
XCP – The Standard Protocol
for ECU Development
Fundamentals and Application Areas
Andreas Patzer | Rainer Zaiser
Andreas Patzer | Rainer Zaiser
XCP – The Standard Protocol for ECU Development
Date April 2014 | Reproduction only with expressed permission from
Vector Informatik GmbH, Ingersheimer Str. 24, 70499 Stuttgart, Germany
© 2014 by Vector Informatik GmbH. All rights reserved. This book is only intended for personal use, but not for technical or
commercial use. It may not be used as a basis for contracts of any kind. All information in this book was compiled with the
greatest possible care, but Vector Informatik does not assume any guarantee or warranty whatsoever for the correctness of the
information it contains. The liability of Vector Informatik is excluded, except for malicious intent or gross negligence, to the extent
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Information contained in this book may be protected by copyright and / or patent rights. Product names of software, hardware and
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whether or not they are identified as registered brands.
XCP –
The Standard Protocol
for ECU Development
Fundamentals and Application Areas
Andreas Patzer, Rainer Zaiser
Vector Informatik GmbH
Table of Contents
Introduction
7
1 Fundamentals of the XCP Protocol
13
1.1 XCP Protocol Layer
19
1.1.1 Identification Field
21
1.1.2 Time Stamp
21
1.1.3 Data Field
22
1.2 Exchange of CTOs
22
1.2.1 XCP Command Structure
22
1.2.2 CMD
25
1.2.3 RES
28
1.2.4 ERR
28
1.2.5 EV
29
1.2.6 SERV
29
1.2.7 Calibrating Parameters in the Slave
29
1.3 Exchanging DTOs – Synchronous Data Exchange
32
1.3.1 Measurement Methods: Polling versus DAQ
33
1.3.2 DAQ Measurement Method
34
1.3.3 STIM Calibration Method
41
1.3.4 XCP Packet Addressing for DAQ and STIM
42
1.3.5 Bypassing = DAQ + STIM
44
1.4 XCP Transport Layers
45
1.4.1 CAN
45
1.4.2 CAN FD
48
1.4.3 FlexRay
50
1.4.4 Ethernet
53
1.4.5 SxI
55
1.4.6 USB
55
1.4.7 LIN
55
1.5 XCP Services
56
1.5.1 Memory Page Swapping
56
1.5.2 Saving Memory Pages – Data Page Freezing
58
1.5.3 Flash Programming
58
1.5.4 Automatic Detection of the Slave
60
1.5.5 Block Transfer Mode for Upload, Download and Flashing
61
1.5.6 Cold Start Measurement (start of measurement during power-on)
62
1.5.7 Security Mechanisms with XCP
63
2 ECU Description File A2L
65
2.1 Setting Up an A2L File for an XCP Slave
68
2.2 Manually Creating an A2L File
69
2.3 A2L Contents versus ECU Implementation
70
3 Calibration Concepts
73
3.1 Parameters in Flash
74
3.2 Parameters in RAM
76
3.3 Flash Overlay
78
3.4 Dynamic Flash Overlay Allocation
79
3.5 RAM Pointer Based Calibration Concept per AUTOSAR
80
3.5.1 Single Pointer Concept
80
3.5.2 Double Pointer Concept
82
3.6 Flash Pointer Based Calibration Concept
83
4 Application Areas of XCP
85
4.1 MIL: Model in the Loop
87
4.2 SIL: Software in the Loop
88
4.3 HIL: Hardware in the Loop
89
4.4 RCP: Rapid Control Prototyping
91
4.5 Bypassing
92
4.6 Shortening Iteration Cycles with Virtual ECUs
95
5 Example of an XCP Implementation
99
5.1 Description of Functions
102
5.2 Parameterization of the Driver
104
The Authors
106
Table of Abbreviations and Acronyms
108
Literature
109
Web Addresses
109
Table of Figures
110
Appendix – XCP Solutions at Vector
112
Index
114
Introduction
7
Introduction
In optimal parameterization (calibration) of electronic ECUs, you calibrate parameter values
during the system runtime and simultaneously acquire measured signals. The physical connec-
tion between the development tool and the ECU is via a measurement and calibration protocol.
XCP has become established as a standard here.
First, the fundamentals and mechanisms of XCP will be explained briefly and then the applica-
tion areas and added value for ECU calibration will be discussed.
First, some facts about XCP:
> XCP signifies “Universal Measurement and Calibration Protocol”. The “X” stands for the vari-
able and interchangeable transport layer.
> It was standardized by an ASAM working committee (Association for Standardisation of Auto-
mation and Measuring Systems). ASAM is an organization of automotive OEMs, suppliers and
tool producers.
> XCP is the protocol that succeeds CCP (CAN Calibration Protocol).
> The conceptual idea of the CAN Calibration Protocol was to permit read and write access to
internal ECU data over CAN. XCP was developed to implement this capability via different
transmission media. Then one speaks of XCP on CAN, XCP on FlexRay or XCP on Ethernet.
> The primary applications of XCP are measurement and calibration of internal ECU parameters.
Here, the protocol offers the ability to acquire measured values “event synchronous” to pro-
cesses in ECUs. This ensures consistency of the data between one another.
To visualize the underlying idea, we initially view the ECU and the software running in it as
a black box. In a black box, only the inputs into the ECU (e.g. CAN messages and sensor val-
ues) and the output from the ECU (e.g. CAN messages and actuator drives) are acquired. Details
about the internal processing of algorithms are not immediately apparent and can only be
determined from an analysis of the input and output data.
Now imagine that you had a look into the behavior of your ECU with every computation cycle. At
any time, you could acquire detailed information on how the algorithm is running. You would
no longer have a black box, but a white box instead with a full view of internal processes. That
is precisely what you get with XCP!
What contribution can XCP make for the overall development process? To check the functional-
ity of the attained development status, the developer can execute the code repeatedly. In this
way, the developer finds out how the algorithm behaves and what might be optimized. It does
not matter here whether a compiled code runs on a specific hardware or whether it is developed
in a model-based way and the application runs in the form of a model.
A central focus is on the evaluation of the algorithm process. For example, if the algorithm is
running as a model in a development environment, such as Simulink from The MathWorks, it
is helpful to developers if they can also acquire intermediate results to their applications, in
order to obtain findings about other changes. In the final analysis, this method enables noth-
ing other than read access to parameters so that they can be visualized and analyzed – and all
of this at model runtime or retrospectively after a time-limited test run has been completed. A
write access is needed if parameterizations are changed, e.g. if the proportional component of a
8
Introduction
PID controller is modified to adapt the algorithm behavior to the system under control. Regard-
less of where your application runs – focal points are always the detailed analysis of algorithm
processes and optimization by changes to the parameterization.
This generalization can be made: The algorithms may exist in any type of executable form (code
or model description). Different systems may be used as the runtime environment (Simulink,
as DLL on the PC, on a rapid prototyping platform, in the ECU etc.). Process flows are analyzed
by read access to data and acquisition of its time-based flow. Parameter sets are modified iter-
atively to optimize algorithms. To simplify the representation, the acquisition of data can be
externalized to an external PC-based tool, although it is understood here that runtime environ-
ments themselves can even offer analysis capabilities.
Runtime Environment
Application
Figure 1:
Communication
PC Tool
Fundamental
Operating System
communication
with a runtime
environment
The type of runtime environment and the form of communication generally differ from one
another considerably. The reason is that the runtime environments are developed by different
producers and are based on different solution approaches. Different types of protocols, con-
figurations, measurement data formats, etc. make it a futile effort to try to exchange parame-
ter sets and results in all development steps. In the end, however, all of these solutions can be
reduced to read and write access at runtime. And there is a standard for this: XCP.
XCP is an ASAM standard whose Version 1.0 was released in 2003. The acronym ASAM stands
for “Association for Standardisation of Automation and Measuring Systems.” Suppliers, vehicle
OEMs and tool manufacturers are all represented in the ASAM working group. The purpose of the
XCP working group is to define a generalized measurement and calibration protocol that can be
used independent of the specific transport medium. Experience gained from working with CCP
(CAN Calibration Protocol) flowed into the development as well.
XCP was defined based on the ASAM interfaces model. The following figure shows a measure-
ment and calibration tool’s interfaces to the XCP Slave, to the description file and the connec-
tion to a higher-level automation system.
Introduction
9
Upper Level
Automation System
ASAM MCD 3MC
Measurement and
ASAM
Calibration System
MCD 2MC
*.a2L
XCP Driver
ECU Description File
ASAM MCD 1MC
XCP Driver
ECU
Figure 2:
The Interface Model
of ASAM
Interface 1: “ASAM MCD-1 MC” between the ECU and the measurement and calibration system
This interface describes the physical and the protocol-specific parts. Strictly speaking, a dis-
tinction was made between interfaces ASAP1a and ASAP1b here. The ASAP1b interface, how-
ever, never received general acceptance and for all practical purposes it has no relevance today.
The XCP protocol is so flexible that it can practically assume the role of a general manufacturer-
independent interface. For example, today all measurement and calibration hardware manufac-
turers offer systems (xETK, VX1000, etc.) which can be connected via the XCP on Ether net stan-
dard. An ASAP1b interface – as it was still described for CCP – is no longer necessary.
Interface 2: “ASAM MCD-2 MC” A2L ECU description file
As already mentioned, XCP works in an address-oriented way. Read or write accesses to objects
are always based on an address entry. Ultimately, however, this would mean that the user would
have to search for his ECU objects in the Master based on the address. That would be extremely
inconvenient. To let users work with symbolic object names, for example, a file is needed that
describes the relationship between the object name and the object address. The next chapter is
devoted to this A2L description file.
Interface 3: “ASAM MCD-3 MC” automation interface
This interface is used to connect another system to the measurement and calibration tool, e.g.
for test bench automation. The interface is not further explained in this document, because it is
irrelevant to understanding XCP.
10
Introduction
XCP is based on the Master-Slave principle. The ECU is the Slave and the measurement and cali-
bration tool is the Master. A Slave may only communicate with one Master at any given time; on
the other hand, the Master can simultaneous communicate with many Slaves.
Master
Bus
Figure 3:
An XCP Master can
simultaneously
Slave
Slave
Slave
Slave
communicate with
multiple Slaves
To be able to access data and configurations over the entire development process, XCP must
be used in every runtime environment. Fewer tools would need to be purchased, operated and
maintained. This would also eliminate the need for manual copying of configurations from one
tool to another, a process that is susceptible to errors. This would simplify iterative loops, in
which results from later work steps are transferred back to prior work steps.
But let us turn our attention away from what might be feasible to what is possible today: every-
thing! XCP solutions are already used in a wide variety of work environments. It is the intention
of this book to describe the main properties of the measurement and calibration protocol and
introduce its use in the various runtime environments. What you will not find in this book: nei-
ther the entire XCP specification in detailed form, nor precise instructions for integrating XCP
drivers in a specific runtime environment. It explains the relationships, but not the individual
protocol and implementation details. Internet links in the appendix refer to openly available
XCP driver source code and sample implementations, which let you understand and see how the
implementation is made.
Screenshots of the PC tool used in this book were prepared using the CANape measurement and
calibration tool from Vector. Other process flows are also explained based on CANape, including
how to create an A2L file and even more. With a cost-free demo version, which is available to you
in the Download Center of the Vector website at www.vector.com/canape_demo, you can see for
yourself.
Introduction
11
12
1 Fundamentals of the XCP Protocol
13
1 Fundamentals of the XCP Protocol
14
1 Fundamentals of the XCP Protocol
Interface 1 of the ASAM interfaces model describes sending and receiving commands and data
between the Slave and the Master. To achieve independence from a specific physical transport
layer, XCP was subdivided into a protocol layer and a transport layer.
CAN
Ethernet
FlexRay
SxI
USB
...
Figure 4: Subdivision of the XCP protocol into protocol layer and transport layer
Depending on the transport layer, one refers to XCP on CAN, XCP on Ethernet, etc. The extend-
ibility to new transport layers was proven as early as 2005 when XCP on FlexRay made its debut.
The current version of the XCP protocol is Version 1.1, which was approved in 2008.
Adherence to the following principles was given high priority in designing the protocol:
> Minimal resource usage in the ECU
> Efficient communication
> Simple Slave implementation
> Plug-and-play configuration with just a small number of parameters
> Scalability
1 Fundamentals of the XCP Protocol
15
A key functionality of XCP is that it enables read and write access to the memory of the Slave.
Read access lets users measure the time response of an internal ECU parameter. ECUs are sys-
tems with discrete time behavior, whose parameters only change at specific time intervals: only
when the processor recalculates the value and updates it in RAM. One of the great strengths of
XCP lies in acquiring measured values from RAM which change synchronously to process flows
or events in the ECU. This lets users evaluate direct relationships between time-based process
flows in the ECU and the changing values. These are referred to as event-synchronous measure-
ments. The related mechanisms will be explained later in detail.
Write access lets the user optimize parameters of algorithms in the Slave. The accesses are
address-oriented, i.e. the communication between Master and Slave references addresses in
memory. So, the measurement of a parameter is essentially implemented as a request of the
Master to the Slave: “Give me the value of memory location 0x1234”. Calibration of a parameter
– the write access – to the Slave means: “Set the value at address 0x9876 to 5”.
An XCP Slave does not absolutely need to be used in ECUs. It may be implemented in differ-
ent environments: from a model-based development environment to hardware-in-the-loop and
software-in-the-loop environments to hardware interfaces that are used to access ECU memory
via debug interfaces such as JTAG, NEXUS and DAP.
Simulink
Slave
Prototype or
ECU Hardware
Slave
XCP
Measurement/
Calibration
Master
Slave
PC
Hardware*
EXE/DLL
Slave
Figure 5:
HIL/SIL Systems
XCP Slaves can be
Slave
used in many
different runtime
* Debug Interfaces, Memory Emulator, ...
environments
16
1 Fundamentals of the XCP Protocol
How can algorithms be optimized using read and write access to the ECU and what benefits
does this offer? To be able to modify individual parameters at runtime in the ECU, there must be
access to them. Not every type of memory permits this process. It is only possible to perform a
read and write access to memory addresses in RAM (intentionally excluding the EEPROM here).
The following is a brief summary of the differences between individual memory technologies:
knowledge of them is very important to understanding over the further course of this book.
Memory Fundamentals
Today, flash memories are usually integrated in the microcontroller chips for ECUs and are used
for long-term storage of code and data, even without power supply. The special aspect of a flash
memory is that read and write access to individual bytes is indeed possible at any time, but writ-
ing of new contents can only be done blockwise, usually in rather large blocks.
Flash memories have a limited life, which is specified in terms of a maximum number of erasure
cycles (depending on the specific technology the maximum may be up to one million cycles).
This is also the maximum number of write cycles, because the memory must always be erased as
a block before it can be written again. The reason for this lies in the memory structure: electrons
are “pumped” via tunnel diodes. A bit is stored at a memory location as follows: electrons must
be transported into the memory location over an electrically insulating layer. Once the elec-
trons are then behind the insulating layer, they form an electric field with their charge, which is
interpreted as a 1 when reading the memory location. If there are no electrons behind the layer,
the cell information is interpreted as a 0. A 1 can indeed be set in this way, but not a 0. Setting
to 0 (= erasing the 1) is performed in a separate erasing routine, in which electrons existing
behind the insulating layer are discharged. However, for architectural reasons, such an erasing
routine does not just act on single bytes, rather only on the group or block level. Depending on
the architecture, blocks of 128 or 256 bytes are usually used. If one wishes to overwrite a byte
within such a block, the entire block must first be erased. Then the entire contents of the block
can be written back.
When this erasing routine is repeated multiple times, the insulating layer (“Tunnel Oxide Film”)
can be damaged. This means that the electrons could slowly leak away, changing some of the
information from 1 to 0 over the course of time. Therefore, the number of allowable flash cycles
is severely limited in an ECU. In the production ECU, it is often only on the order of single digit
numbers. This restriction is monitored by the Flash Boot Loader, which uses a counter to keep
track of how many flash operations have already been executed. When the specified number is
exceeded, the Flash Boot Loader rejects another flash request.
A RAM (Random Access Memory) requires a permanent power supply; otherwise it loses its con-
tents. While flash memory serves the purpose of long-term storage of the application, the RAM
is used to buffer computed data and other temporary information. Shutting off the power sup-
ply causes the RAM contents to be lost. In contrast to flash memory, it is easy to read and write
to RAM.
1 Fundamentals of the XCP Protocol
17
This fact is clear: if parameters need to be changed at runtime, it must be assured that they are
located in RAM. It is really very important to understand this circumstance. That is why we will
look at the execution of an application in the ECU based on the following example:
In the application, the y parameters are computed from the sensor values x.
// Pseudo-code representation
a = 5;
b = 2;
y = a * x + b;
If the application is flashed in the ECU, the controller handles this code as follows after booting:
the values of the x parameters correspond to a sensor value. At some time point, the application
must therefore poll the sensor value and the value is then stored in a memory location assigned
to the x parameters. Since this value always needs to be rewritten at runtime, the memory loca-
tion can only lie in RAM.
The parameter y is computed. The values a and b, as factor and offset, are included as informa-
tion in flash memory. They are stored as constants there. The value of y must also be stored in
RAM, because once again that is the only place where write access is possible. At precisely which
location in RAM the parameters x and y are located, or where a and b lie in flash, is set in the
compiler/linker run. This is where objects are allocated to unique addresses. The relationship
between object name, data type and address is documented in the linker-map file. The linker-
map file is generated by the Linker run and can exist in different formats. Common to all for-
mats, however, is that they contain the object name and address at a minimum.
In the example, if the offset b and factor a depend on the specific vehicle, the values of a and b
must be individually adapted to the specific conditions of the vehicle. This means that the algo-
rithm remains as it is, but the parameter values change from vehicle to vehicle.
In the normal operating mode of an ECU, the application runs from the flash memory. It does
not permit any write accesses to individual objects. This means that parameter values which are
located in the flash area cannot be modified at runtime. If a change to parameter values should
be possible during runtime, the parameters to be modified must lie in RAM and not in flash.
Now, how do the parameters and their initial values make their way into RAM? How does one
solve the problem of needing to modify more parameters than can be simultaneously stored in
RAM? These issues lead us to the topic of calibration concepts (see chapter 3).
18
1 Fundamentals of the XCP Protocol
Summary of XCP fundamentals
Read and write accesses to memory contents are available with the mechanisms of the XCP pro-
tocol. The accesses are made in an address-oriented way. Read access enables measurement of
parameters from RAM, and write access enables calibration of the parameters in RAM. XCP per-
mits execution of the measurement synchronous to events in the ECU. This ensures that the
measured values correlate with one another. With every restart of a measurement, the signals
to be measured can be freely selected. For write access, the parameters to be calibrated must be
stored in RAM. This requires a calibration concept.
This leads to two important questions:
> How does the user of the XCP protocol know the correct addresses of the measurement and
calibration parameters in RAM?
> What does the calibration concept look like?
The first question is answered in chapter 2 “ECUs description file A2L”. The topic of the calibra-
tion concept is addressed in chapter 3.
1.1 XCP Protocol Layer
19
1.1 XCP Protocol Layer
XCP data is exchanged between the Master and Slave in a message-based way. The entire “XCP
message frame” is embedded in a frame of the transport layer (in the case of XCP on Ethernet
with UDP in a UDP packet). The frame consists of three parts: the XCP header, the XCP packet
and the XCP tail.
In the following figure, part of a message is shown in red. It is used to send the current XCP
frame. The XCP header and XCP tail depend on the transport protocol.
XCP Message (Frame)
XCP Header
XCP Packet
XCP Tail
PID FILL
DAQ
TIMESTAMP
DATA
Identification
Timestamp
Data
Field
Field
Field
Figure 6: XCP packet
The XCP packet itself is independent of the transport protocol used. It always contains three
components: “Identification Field”, “Timestamp Field” and the current data field “Data Field”.
Each Identification Field begins with the Packet Identifier (PID), which identifies the packet.
The following overview shows which PIDs have been defined:
PID for frames
PID for frames
from Master to Slave
from Slave to Master
0xFF
0xFF
RES
0xFE
ERR
CMD
....
0xFD
EV
0xC0
0xFC
SERV
0xBF
0xFB
absolute or
absolute or
relative
relative
....
ODT number
....
ODT number
for STIM
for STIM
0x00
0x00
Figure 7: Overview of XCP Packet Identifier (PID)
20
1 Fundamentals of the XCP protocol
Communication via the XCP packet is subdivided into one area for commands (CTO) and one area
for sending synchronous data (DTO).
XCP Master
XCP Driver
CTO
DTO
CMD
RES
ERR
EV
SERV
DAQ
STIM
Command / Response / Error / Event /
DAQ
STIM
Service Request Processor
Processor
Processor
Bypass
XCP Handler
PGM
CAL
DAQ
STIM
Resources
Figure 8:
XCP Slave
XCP communication
model with CTO/DTO
The acronyms used here stand for
CMD
Command Packet
sends commands
RES
Command Response Packet
positive response
ERR
Error
negative response
EV
Event Packet
asynchronous event
SERV
Service Request Packet
service request
DAQ
Data AcQuisition
send periodic measured values
STIM
Stimulation
periodic stimulation of the Slave
Commands are exchanged via CTOs (Command Transfer Objects). The Master initiates contact in
this way, for example. The Slave must always respond to a CMD with RES or ERR. The other CTO
messages are sent asynchronously. The Data Transfer Objects (DTO) are used to exchange syn-
chronous measurement and stimulation data.
1.1 XCP Protocol Layer
21
1.1.1 Identification Field
XCP Packet
PID FILL DAQ
TIMESTAMP
DATA
Figure 9:
Identification Field
Message
identification
When messages are exchanged, both the Master and Slave must be able to determine which
message was sent by the other. This is accomplished in the identification field. That is why each
message begins with the Packet Identifier (PID).
In transmitting CTOs, the PID field is fully sufficient to identify a CMD, RES or other CTO packet.
In Figure 7, it can be seen that commands from the Master to the Slave utilize a PID from 0xC0 to
0xFF. The XCP Slave responds or informs the Master with PIDs from 0xFC to 0xFF. This results in a
unique allocation of the PIDs to the individually sent CTOs.
When DTOs are transmitted, other elements of the identification field are used (see chapter
1.3.4 “XCP Packet Addressing for DAQ and STIM”).
1.1.2 Time Stamp
XCP Packet
PID FILL DAQ
TIMESTAMP
DATA
Figure 10:
Time stamp
DTO packets use time stamps, but this is not possible in transmission of a CTO message. The
Slave uses the time stamp to supply time information with measured values. That is, the Mas-
ter not only has the measured value, but also the time point at which the measured value was
acquired. The amount of time it takes for the measured value to arrive at the Master is no lon-
ger important, because the relationship between the measured value and the time point comes
directly from the Slave.
Transmission of a time stamp from the Slave is optional. This topic is discussed further in
ASAM XCP Part 2 Protocol Layer Specification.
22
1 Fundamentals of the XCP protocol
1.1.3 Data Field
XCP Packet
PID FILL DAQ
TIMESTAMP
DATA
Figure 11:
Data field
Data Field
in the XCP packet
Finally, the XCP packet also contains the data stored in the data field. In the case of CTO
packets, the data field consists of specific parameters for the different commands. DTO
packets contain the measured values from the Slave and when STIM data is sent the values from
the Master.
1.2 Exchange of CTOs
CTOs are used to transmit both commands from the Master to the Slave and responses from the
Slave to the Master.
1.2.1 XCP Command Structure
The Slave receives a command from the Master and must react to it with a positive or negative
response. The communication structure is always the same here:
Command (CMD):
Position
Type Description
0
BYTE
Command Packet Code CMD
1..MAX_CTO-1
BYTE
Command specific Parameters
A unique number is assigned to each command. In addition, other specific parameters may be
sent with the command. The maximum number of parameters is defined as MAX_CTO-1 here.
MAX_CTO indicates the maximum length of the CTO packets in bytes.
Positive response:
Position Type Description
0
BYTE
Command Positive Response Packet Code = RES 0xFF
1..MAX_CTO-1
BYTE
Command specific Parameters
1.2 Exchange of CTOs
23
Negative response:
Position
Type Description
0
BYTE
Error Packet Code = 0xFE
1
BYTE
Error code
2..MAX_CTO-1
BYTE
Command specific Parameters
Specific parameters can be transmitted as supplemental information with negative responses as
well and not just with positive responses. One example is when the connection is made between
Master and Slave. At the start of a communication between Master and Slave, the Master sends
a connect request to the Slave, which in turn must respond positively to produce a continuous
point-to-point connection.
Master à Slave: Connect
Slave à Master: Positive response
Connect command:
Position Type Description
0
BYTE
Command Code = 0xFF
1
BYTE Mode
00 = Normal
01 = user defined
Mode 00 means that the Master wishes XCP communication with the Slave. If the Master uses
0xFF 0x01 when making the connection, the Master is requesting XCP communication with the
Slave. Simultaneously, it informs the Slave that it should switch to a specific – user-defined
– mode.
Positive response of the Slave:
Position Type Description
0
BYTE
Packet ID: 0xFF
1
BYTE RESOURCE
2
BYTE COMM_MODE_BASIC
3
BYTE
MAX_CTO, Maximum CTO size [BYTE]
4
WORD
MAX_DTO, Maximum DTO size [BYTE]
6
BYTE
XCP Protocol Layer Version Number (most significant byte only)
7
BYTE
XCP Transport Layer Version Number (most significant byte only)
The positive response of the Slave can assume a somewhat more extensive form. The Slave
already sends communication-specific information to the Master when making the connection.
RESOURCE, for example, is information that the Slave gives on whether it supports such features
as page switching or whether flashing over XCP is possible. With MAX_DTO, the Slave informs the
Master of the maximum packet length it supports for transfer of the measured values, etc. You
will find details on the parameters in ASAM XCP Part 2 Protocol Layer Specification.
24
1 Fundamentals of the XCP protocol
XCP permits three different modes for exchanging commands and reactions between Master and
Slave: Standard, Block and Interleaved mode.
Standard Mode
Block Mode
Interleaved Mode
Master
Slave Master
Slave
Master
Slave
Request k
Request k
Part1
Request k
Part2
MIN_ST
Part3
Request k+1
Response k
MAX_BS
Response k
Request k+1
Response k
Request k+1
Response k+1
Response k+1
Part1
Response k+1
Part2
Part3
Time
Time
Time
Figure 12: The three modes of the XCP protocol: Standard, Block and Interleaved mode
In the standard communication model, each request to a Slave is followed by a single response.
Except with XCP on CAN, it is not permitted for multiple Slaves to react to a command from the
Master. Therefore, each XCP message can always be traced back to a unique Slave. This mode is
the standard case in communication.
The block transfer mode is optional and saves time in large data transfers (e.g. upload or
download operations). Nonetheless, performance issues must be considered in this mode
in the direction of the Slave. Therefore, minimum times between two commands (MIN_ST)
must be maintained and the total number of commands must be limited to an upper limit
MAX_BS. Optionally, the Master can read out these communication settings from the Slave with
GET_COMM_MODE_INFO. The aforementioned limitations do not need to be observed in block
transfer mode in the direction of the Master, because performance of the PC nearly always suf-
fices to accept the data from a microcontroller.
The interleaved mode is also provided for performance reasons. But this method is also optional
and – in contrast to block transfer mode – it has no relevance in practice.
1.2 Exchange of CTOs
25
1.2.2 CMD
XCP CTO Packet
PID
DATA
Data Field
Identification Field
Timestamp Field
empty for CTO
Figure 13: Overview of the CTO packet structure
The Master sends a general request to the Slave over CMD. The PID (Packet Identifier) field
contains the identification number of the command. The additional specific parameters are
transported in the data field. Then the Master waits for a reaction of the Slave in the form of a
RESponse or an ERRor.
XCP is also very scalable in its implementation, so it is not necessary to implement every com-
mand. In the A2L file, the available CMDs are listed in what is known as the XCP IF_DATA. If there
is a discrepancy between the definition in the A2L file and the implementation in the Slave, the
Master can determine, based on the Slave’s reaction, that the Slave does not even support the
command. If the Master sends a command that is not implemented in the Slave, the Slave must
acknowledge with ERR_CMD_UNKNOWN and no further activities are initiated in the Slave. This
lets the Master know quickly that an optional command has not been implemented in the Slave.
Some other parameters are included in the commands as well. Please take the precise details
from the protocol layer specification in document ASAM XCP Part 2.
The commands are organized in groups: Standard, Calibration, Page, Programming and DAQ
measurement commands. If a group is not needed at all, its commands do not need to be imple-
mented. If the group is necessary, certain commands must always be available in the Slave,
while others from the group are optional.
The following overview serves as an example. The SET_CAL_PAGE and GET_CAL_PAGE commands
in the Page-Switching group are identified as not optional. This means that in an XCP Slave that
supports Page Switching at least these two commands must be implemented. If Page-Switching
support is unnecessary in the Slave, these commands do not need to be implemented. The same
applies to other commands.
26
1 Fundamentals of the XCP protocol
Standard commands:
Command PID Optional
CONNECT 0xFF No
DISCONNECT 0xFE No
GET_STATUS 0xFD No
SYNCH
0xFC No
GET_COMM_MODE_INFO 0xFB
Yes
GET_ID
0xFA Yes
SET_REQUEST 0xF9 Yes
GET_SEED 0xF8 Yes
UNLOCK
0xF7 Yes
SET_MTA
0xF6 Yes
UPLOAD
0xF5 Yes
SHORT_UPLOAD 0xF4
Yes
BUILD_CHECKSUM 0xF3
Yes
TRANSPORT_LAYER_CMD 0xF2
Yes
USER_CMD 0xF1 Yes
Calibration commands:
Command PID Optional
DOWNLOAD 0xF0 No
DOWNLOAD_NEXT 0xEF
Yes
DOWNLOAD_MAX 0xEE
Yes
SHORT_DOWNLOAD 0xED
Yes
MODIFY_BITS 0xEC Yes
Standard commands:
Command PID Optional
SET_CAL_PAGE 0xEB No
GET_CAL_PAGE 0xEA No
GET_PAG_PROCESSOR_INFO 0xE9
Yes
GET_SEGMENT_INFO 0xE8
Yes
GET_PAGE_INFO 0xE7
Yes
SET_SEGMENT_MODE 0xE6
Yes
GET_SEGMENT_MODE 0xE5
Yes
COPY_CAL_PAGE 0xE4
Yes
1.2 Exchange of CTOs
27
Periodic data exchange – basics:
Command PID Optional
SET_DAQ_PTR 0xE2 No
WRITE_DAQ 0xE1 No
SET_DAQ_LIST_MODE 0xE0
No
START_STOP_DAQ_LIST 0xDE
No
START_STOP_SYNCH 0xDD
No
WRITE_DAQ_MULTIPLE 0xC7
Yes
READ_DAQ 0xDB Yes
GET_DAQ_CLOCK 0xDC
Yes
GET_DAQ_PROCESSOR_INFO 0xDA
Yes
GET_DAQ_RESOLUTION_INFO 0xD9
Yes
GET_DAQ_LIST_INFO 0xD8
Yes
GET_DAQ_EVENT_INFO 0xD7
Yes
Periodic data exchange – static configuration:
Command PID Optional
CLEAR_DAQ_LIST 0xE3
No
GET_DAQ_LIST_INFO 0xD8
Yes
Periodic data exchange – dynamic configuration:
Command PID Optional
FREE_DAQ 0xD6 Yes
ALLOC_DAQ 0xD5 Yes
ALLOC_ODT 0xD4 Yes
ALLOC_ODT_ENTRY 0xD3
Yes
28
1 Fundamentals of the XCP protocol
Flash programming:
Command PID Optional
PROGRAM_START 0xD2
No
PROGRAM_CLEAR 0xD1
No
PROGRAM 0xD0 No
PROGRAM_RESET 0xCF
No
GET_PGM_PROCESSOR_INFO 0xCE
Yes
GET_SECTOR_INFO 0xCD
Yes
PROGRAM_PREPARE 0xCC
Yes
PROGRAM_FORMAT 0xCB
Yes
PROGRAM_NEXT 0xCA
Yes
PROGRAM_MAX 0xC9
Yes
PROGRAM_VERIFY 0xC8
Yes
1.2.3 RES
If the Slave is able to successfully comply with a Master’s request, it gives a positive acknowl-
edge with RES.
Position
Type Description
0
BYTE
Packet Identifier = RES 0xFF
1..MAX_CTO-1
BYTE
Command response data
You will find more detailed information on the parameters in ASAM XCP Part 2 Protocol Layer
Specification.
1.2.4 ERR
If the request from the Master is unusable, it responds with the error message ERR and an error
code.
Position
Type Description
0
BYTE
Packet Identifier = ERR 0xFE
1
BYTE
Error code
2..MAX_CTO-1
BYTE
Optional error information data
You will find a list of possible error codes in ASAM XCP Part 2 Protocol Layer Specification.
1.2 Exchange of CTOs
29
1.2.5 EV
If the Slave wishes to inform the Master of an asynchronous event, an EV can be sent to do this.
Its implementation is optional.
Position
Type Description
0
BYTE
Packet Identifier = EV 0xFD
1
BYTE
Event code
2..MAX_CTO-1
BYTE
Optional event information data
You will find more detailed information on the parameters in ASAM XCP Part 2 Protocol Layer
Specification.
Events will be discussed much more in relation to measurements and stimulation. This has noth-
ing to do with the action of the XCP Slave that initiates sending of an EVENT. Rather it involves
the Slave reporting a disturbance such as the failure of a specific functionality.
1.2.6 SERV
The Slave can use this mechanism to request that the Master execute a service.
Position Type Description
0
BYTE
Packet Identifier = SERV 0xFC
1
BYTE
Service request code
2..MAX_CTO-1
BYTE
Optional service request data
You will find the Service Request Code table in ASAM XCP Part 2 Protocol Layer Specification.
1.2.7 Calibrating Parameters in the Slave
To change a parameter in an XCP Slave, the XCP Master must send the parameter’s location as
well as the value itself to the Slave.
XCP always defines addresses with five bytes: four for the actual address and one byte for the
address extension. Based on a CAN transmission, only seven useful bytes are available for XCP
messages. For example, if the calibrator sets a 4-byte value and wants to send both pieces of
information in one CAN message, there is insufficient space to do this. Since a total of nine
bytes are needed to transmit the address and the new value, the change cannot be transmit-
ted in one CAN message (seven useful bytes). The calibration request is therefore made with
two messages from Master to Slave. The Slave must acknowledge both messages and in sum four
messages are exchanged.
30
1 Fundamentals of the XCP protocol
The following figure shows the communication between Master and Slave, which is necessary to
set a parameter value. The actual message is located in the line with the envelope symbol. The
interpretation of the message is shown by “expanding” it with the mouse.
Figure 14: Trace example from a calibration process
In the first message of the Master (highlighted in gray in Figure 14), the Master sends the
command SET_MTA to the Slave with the address to which a new value should be written. In
the second message, the Slave gives a positive acknowledge to the command with Ok:SET_MTA.
The third message DOWNLOAD transmits the hex value as well as the valid number of bytes.
In this example, the valid number of bytes is four, because it is a float value. The Slave gives
another positive acknowledge in the fourth message.
This completes the current calibration process. In the Trace display, you can recognize a termi-
nating SHORT_UPLOAD – a special aspect of CANape, the measurement and calibration tool from
Vector. To make sure that the calibration was performed successfully, the value is read out again
after the process and the display is updated with the read-out value. This lets the user directly
recognize whether the calibration command was implemented. This command also gets a posi-
tive acknowledge with Ok:SHORT_UPLOAD.
When the parameter changes in the ECU’s RAM, the application processes the new value. A
reboot of the ECU, however, would lead to erasure of the value and overwriting of the value in
RAM with the original value from the flash (see chapter 3 “Calibration Concepts”). So, how can
the modified parameter set be permanently saved?
1.2 Exchange of CTOs
31
Essentially, there are two possibilities:
A) Save the parameters in the ECU
The changed data in RAM could for example be saved in the ECU’s EEPROM: either automatically
when ramping down the ECU, or manually by the user. A prerequisite is that the data can be
stored in a nonvolatile memory of the Slave. In an ECU, this would be the EEPROM or flash. ECUs
with thousands of parameters, however, are seldom able to provide so much unused EEPROM
memory space, so this method is rare.
Another possibility is to write the RAM parameters back into the ECU’s flash memory. This
method is relatively complex. A flash memory must first be erased before it can be rewritten.
This, in turn, can only be done as a block. Consequently, it is not simply a matter of writing back
individual bytes. You will find more on this topic in chapter 3 “Calibration Concepts”.
B) Save the parameters in the form of a file on the PC
It is much more common to store the parameters on the PC. All parameters – or subsets of them
– are stored in the form of a file. Different formats are available for this; the simplest case is
that of an ASCII text file, which only contains the name of the object and its value. Other for-
mats also permit saving other information, such as findings about the maturity level of the
parameter of the history of revisions.
Scenario: After finishing his or her work, the calibrator wishes to enjoy a free evening. So, the
calibrator saves the executed changes in the ECU’s RAM in the form of a parameter set file on a
PC. The next day, the calibrator wants to continue working where he or she left off. The calibra-
tor starts the ECU. Upon booting, the parameters are initialized in RAM. However, the ECU does
this using values stored in flash. This means that the changes of the previous day are no longer
available in the ECU. To now continue where work was left off on the previous day, the calibra-
tor transfers the contents of the parameter set file to the ECU’s RAM by XCP using the DOWNLOAD
command.
Figure 15: Transfer of a parameter set file to an ECU’s RAM
32
1 Fundamentals of the XCP protocol
Saving parameter set file in hex files and flashing
Flashing an ECU is another way to change the parameters in flash. They are then written to RAM
as new parameters when the ECU is booted. A parameter set file can also be transferred to a C or
H file and be made into the new flash file with another compiler/linker run. However, depend-
ing on the parameters of the code, the process of generating a flashable hex file could take a
considerable amount of time. In addition, the calibrator might not have any ECU source code
– depending on the work process. That would prevent this method from being available to the
calibrator.
As an alternative, the calibrator can copy the parameter set file into the existing flash file.
Figure 16: Hex window
In the flash file, there is a hex file that contains both the addresses and the values. Now a
parameter file can be copied to a hex file. To do this, CANape takes the address and the value
from the parameter set file and updates the parameter value at the relevant location in the
hex file. This results in a new hex file, which contains the changed parameter values. However,
this Hex file must now possibly run through further process steps to obtain a flashable file.
One recurring problem here is the checksums, which the ECU checks to determine whether it
received the data correctly. If the flashable file exists, it can be flashed in the ECU and after the
reboot the new parameter values are available in the ECU.
1.3 Exchanging DTOs – Synchronous Data Exchange
As depicted in Figure 8, DTOs (Data Transfer Objects) are available for exchanging synchronous
measurement and calibration data. Data from the Slave are sent to the Master by DAQ – synchro-
nous to internal events. This communication is subdivided into two phases:
In an initialization phase, the Master communicates to the Slave which data the Slave should
send for different events. After this phase, the Master initiates the measurement in the Slave
and the actual measurement phase begins. From this point in time, the Slave sends the desired
data to the Master, which only listens until it sends a “measurement stop” to the Slave. Trigger-
ing of measurement data acquisition and transmission is controlled by events in the ECU.
1.3 Exchanging DTOs – Synchronous Data Exchange
33
The Master sends data to the Slave by STIM. This communication also consists of two phases:
In the initialization phase, the Master communicates to the Slave which data it will send to the
Slave. After this phase, the Master sends the data to the Slave and the STIM processor saves the
data. As soon as a related STIM event is triggered in the Slave, the data is transferred to the
application memory.
1.3.1 Measurement Methods: Polling versus DAQ
Before explaining how event-synchronous, correlated data is measured from a Slave, here is a
brief description of another measurement method known as Polling. It is not based on DTOs, but
on CTOs instead. Actually, this topic should be explained in a separate chapter, but a description
of polling lets us derive, in a very elegant way, the necessity of DTO-based measurement, so a
minor side discussion at this point makes sense.
The Master can use the SHORT_UPLOAD command to request the value of a measurement para-
meter from the Slave. This is referred to as polling. This is the simplest case of a measure -
ment: sending the measured value of a measurement parameter at the time at which the
SHORT_UPLOAD command has been received and executed.
In the following example, the measurement parameter “Triangle” is measured from the Slave:
Figure 17:
Address information
of the parameter
“Triangle” from the
A2L file
The address 0x60483 is expressed as an address with five bytes in the CAN frame: one byte for
the address extension and four bytes for the actual address.
34
1 Fundamentals of the XCP protocol
Figure 18: Polling communication in the CANape Trace window
The XCP specification sets a requirement for polling: that the value of each measurement param-
eter must be polled individually. For each value to be measured via polling, two messages must
go over the bus: the Master’s request to the Slave and the Slave’s response to the Master.
Besides this additional bus load, there is another disadvantage of the polling method: When
polling multiple data values, the user normally wants the data to correlate to one another. How-
ever, multiple values that are measured sequentially with polling do not necessarily stand in
correlation to one another, i.e. they might not originate from the same ECU computing cycle.
This limits the suitability of polling for measurement, because it produces unnecessarily high
data traffic and the measured values are not evaluated in relation to the process flows in the
ECU.
So, an optimized measurement must solve two tasks:
> Bandwidth optimization during the measurement
> Assurance of data correlation
This task is handled by the already mentioned DAQ method. DAQ stands for Data Acquisition and
it is implemented by sending DTOs (Data Transfer Objects) from the Slave to the Master.
1.3.2 DAQ Measurement Method
The DAQ method solves the two problems of polling as follows:
> The correlation of measured values is achieved by coupling the acquisition of measured val-
ues to the events in the ECU. The measured values are not acquired and transferred until it has
been assured that all computations have been completed.
> To reduce bus load, the measurement process is subdivided into two phases: In a configu-
ration phase, the Master communicates which values it is interested in to the Slave and the
second phase just involves transferring the measured values of the Slave to the Master.
1.3 Exchanging DTOs – Synchronous Data Exchange
35
How can the acquisition of measured values now be coupled to processes in the ECU? Figure 19
shows the relationship between calculation cycles in the ECU and the changes in parameters X
and Y.
Calculation
Calculation
Calculation
cycle n
cycle n+1
cycle n+2
time
10
8
6
X 4 2 0
10
8
6
Y 4 2 0
E1
E1
E1
Figure 19:
Read sensor X
Calculate Y = X
Events in the ECU
Let’s have a look at the sequence in the ECU: When event E1 (= end of computation cycle) is
reached, then all parameters have been acquired and calculations have been made. This means
that all values must match one another and correlate at this time point. This means that we
use an event-synchronous measurement method. This is precisely what is implemented with the
help of the DAQ mechanism: When the algorithm in the Slave reaches the “Computational cycle
completed” event, the XCP Slave collects the values of the measurement parameters, saves them
in a buffer and sends them to the Master. This assumes that the Slave knows which parameters
should be measured for which event.
An event does not absolutely have to be a cyclic, time-equidistant event, rather in the case of
an engine controller, for example, it might be angle-synchronous. This makes the time inter-
val between two events dependent on the engine rpm. A singular event, such as activation of a
switch by the driver, is also an event that is not by any means equidistant in time.
The user selects the signals. Besides the actual measurement object, the user must select the
underlying event for the measurement parameters. The events as well as the possible assign-
ments of the measurement objects to the events must be stored in the A2L file.
Figure 20:
Event definition
in an A2L
36
1 Fundamentals of the XCP protocol
In the normal case, it does not make any sense to be able to simultaneously assign a measured
value to multiple events. Generally, a parameter is only modified within a single cycle (e.g. only
at 10-ms intervals) and not in multiple cycles (e.g. at 10-ms and 100-ms intervals).
Figure 21:
Allocation of
“Triangle” to possible
events in the A2L
Figure 21 shows that the “Triangle” parameter can in principle be measured with the 1 ms,
10 ms and 100 ms events. The default setting is 10 ms.
Measurement parameters are allocated to events in the ECU during measurement configuration
by the user.
Figure 22: Selecting
events (measurement
mode) for each
measurement parameter
After configuring the measured signals, the user starts the measurement. The XCP Master lists
the desired measurement parameters in what are known as DAQ lists. In these lists, the mea-
sured signals are each allocated to selected events. This configuration information is sent to the
Slave before the actual start of measurement. Then the Slave knows which addresses it should
read out and transmit when an event occurs. This distribution of the measurement into a con-
figuration phase and a measurement phase was already mentioned at the very beginning of this
chapter.
This solves both problems that occur in polling: bandwidth is used optimally, because the Mas-
ter no longer needs to poll each value individually during the measurement and the measured
values correlate with one another.
1.3 Exchanging DTOs – Synchronous Data Exchange
37
Figure 23: Excerpt from the CANape Trace window of a DAQ measurement
Figure 23 illustrates an example of command-response communication (color highlighting)
between Master and Slave (overall it is significantly more extensive and is only shown in part
here for reasons of space). This involves transmitting the DAQ configuration to the Slave. After-
wards, the measurement start is triggered and the Slave sends the requested values while the
Master just listens.
Until now, the selection of a signal was described based on its name and allocation to a mea-
surement event. But how exactly is the configuration transferred to the XCP Slave?
Let us look at the problem from the perspective of memory structure in the ECU: The user has
selected signals and wishes to measure them. So that sending a signal value does not require
the use of an entire message, the signals from the Slave are combined into message packets. The
Slave does not create this definition of the combination independently, or else the Master would
not be able to interpret the data when it received the messages. Therefore, the Slave receives
an instruction from the Master describing how it should distribute the values to the messages.
The sequence in which the Slave should assemble the bytes into messages is defined in what
are known as Object Description Tables (ODTs). The address and object length are important to
uniquely identify a measurement object. An ODT provides the allocations of RAM contents from
the Slave to assemble a message on the bus. According to the communication model, this mes-
sage is transmitted as a DAQ DTO (Data Transfer Object).
38
1 Fundamentals of the XCP protocol
RAM Cells
ODT
0
address, length
1
address, length
2
address, length
3
address, length
...
PID
0
1
2
3
...
Figure 24:
ODT: Allocation
of RAM addresses
to DAQ DTO
Stated more precisely, an entry in an ODT list references a memory area in RAM by the address
and length of the object.
After receiving the measurement start command, at some point an event occurs that is asso-
ciated with a measurement. The XCP Slave begins to acquire the data. It combines the indi-
vidual objects into packets and sends them on the bus. The Master reads the bus message and
can interpret the individual data, because it has defined the allocation of individual objects to
packets itself and therefore it knows their relationships.
However, each packet has a maximum number of useful bytes, which depends on the trans-
port medium that is used. In the case of CAN, this amounts to seven bytes. If more data needs
to be measured, an ODT is no longer sufficient. If two or more ODTs need to be used to trans-
mit the measured values, then the Slave must be able to copy the data into the correct ODT and
the Master must be able to uniquely identify the received ODTs. If multiple measurement inter-
vals of the ECU are used, the relationship between ODT and measurement interval must also be
uniquely identifiable.
1.3 Exchanging DTOs – Synchronous Data Exchange
39
The ODTs are combined into DAQ lists in the XCP protocol. Each DAQ list contains a number of
ODTs and is assigned to an event.
ODT #2 0 address, length
1 address, length
ODT #1 0 address, length
2 address, length
1 address, length
ODT #0 0 address, length
3 address, length
2 address, length
1 address, length ...
3 address, length
PID=2 0 1 2 3 ...
2 address, length
...
PID=1 0 1 2 3 ...
3 address, length
Figure 25:
...
PID=0 0 1 2 3 ...
DAQ list
with three ODTs
For example, if the user uses two measurement intervals (= two different events in the ECU),
then two DAQ lists are used as well. One DAQ list is needed per event used. Each DAQ list contains
the entries related to the ODTs and each ODT contains references to the values in the RAM cells.
DAQ lists are subdivided into the types: static, predefined and dynamic.
Static DAQ lists:
If the DAQ lists and ODT tables are permanently defined in the ECU, as is familiar from CCP, they
are referred to as static DAQ lists. There is no definition of which measurement parameters exist
in the ODT lists, rather only the framework that can be filled (in contrast to this, see predefined
DAQ lists).
In static DAQ lists, the definitions are set in the ECU code and are described in the A2L. Figure
26 shows an excerpt of an A2L, in which static DAQ lists are defined:
Figure 26:
Static DAQ lists
In the above example, there is a DAQ list with the number 0, which is allocated to a 10-ms event
and can carry a maximum of two ODTs. The DAQ list with the number 1 has four ODTs and is linked
to the 100 ms event.
40
1 Fundamentals of the XCP protocol
The A2L matches the contents of the ECU. In the case of static DAQ lists, the number of DAQ lists
and the ODT lists they each contain are defined with the download of the application into the
ECU. If the user now attempts to measure more signals with an event than fit in the allocated
DAQ list, the Slave in the ECU will not be able to fulfill the requirements and the configuration
attempt is terminated with an error. It does not matter that the other DAQ list is still fully avail-
able and therefore actually still has transmission capacity.
Predefined DAQ lists:
Entirely predefined DAQ lists can also be set up in the ECU. However, this method is practically
never used in ECUs due to the lack of flexibility for the user. It is different for analog measure-
ment systems which transmit their data by XCP: Flexibility is unnecessary here, since the physi-
cal structure of the measurement system remains the same over its life.
Dynamic DAQ lists:
A special aspect of the XCP protocol are the dynamic DAQ lists. It is not the absolute parameters
of the DAQ and ODT lists that are permanently defined in the ECU code here, but just the param-
eters of the memory area that can be used for the DAQ lists. The advantage is that the measure-
ment tool has more latitude in putting together the DAQ lists and it can manage the structure
of the DAQ lists dynamically.
Various functions especially designed for this dynamic management are available in XCP such as
ALLOC_ODT which the Master can use to define the structure of a DAQ list in the Slave.
MIN_DAQ + DAQ_COUNT
DAQ1
DAQ0
DAQ
ALLOC_
ALLOC_ODT_ENTRY
ODT_ENTERIES_COUNT
T
ALLOC_OD
GRANULARITY_ODT_ENTRY_SIZE_DAQ
Figure 27:
ODT_COUNT
Dynamic DAQ lists
In putting together the DAQ lists, the Master must be able to distinguish whether dynamic or
static DAQ lists are being used, how the parameters and structures of the DAQ lists look, etc.
1.3 Exchanging DTOs – Synchronous Data Exchange
41
1.3.3 STIM Calibration Method
The XCP calibration method was already introduced in the chapter about exchanging CTOs. This
type of calibration exists in every XCP driver and forms the basis for calibrating objects in the
ECU. However, no synchronization exists between sending a calibration command and an event
in the ECU.
In contrast to this, the use of STIM is not based on exchanging CTOs, rather on the use of DTOs
with communication that is synchronized to an event in the Slave. The Master must therefore
know to which events in the Slave it can even synchronize at all. This information must also exist
in the A2L.
Figure 28: Event for DAQ and STIM
If the Master sends data to the Slave by STIM, the XCP Slave must be informed of the location in
the packets at which the calibration parameters can be found. The same mechanisms are used
here as are used for the DAQ lists.
42
1 Fundamentals of the XCP protocol
1.3.4 XCP Packet Addressing for DAQ and STIM
Addressing of the XCP packets was already discussed at the beginning of this chapter. Now that
the concepts of DAQ, ODT and STIM have been introduced, XCP packet addressing will be pre-
sented in greater detail.
During transmission of CTOs, the use of a PID is fully sufficient to uniquely identify a packet;
however, this is no longer sufficient for transmitting measured values. The following figure
offers an overview of the possible addressing that could occur with the DTOs:
XCP DTO Packet
Identification Field Timestamp Field
Data Field
PID
PID DAQ
TS
PID
DAQ
TS
Figure 29:
Structure of the
PID FILL
DAQ
TIMESTAMP
DATA
XCP packet for DTO
transmissions
Transmission type: “absolute ODT numbers”
Absolute means that the ODT numbers are unique throughout the entire communication – i.e.
across all DAQ lists. In turn, this means that the use of absolute ODT numbers assumes a trans-
formation step that utilizes a so-called “FIRST_PID for the DAQ list.
If a DAQ list starts with the PID j, then the PID of the first packet has the value j, the second
packet has the PID value j + 1, the third packet has the PID value j + 2, etc. Naturally, the Slave
must ensure here that the sum of FIRST_PID + relative ODT number remains below the PID of the
next DAQ list.
DAQ list: 0
≤ PID ≤ k
DAQ list: k + 1 ≤ PID ≤ m
DAQ list: m + 1 ≤ PID ≤ n
etc.
1.3 Exchanging DTOs – Synchronous Data Exchange
43
In this case, the identification field is very simple:
Identification Field
PID
Figure 30:
Identification field
absolute ODT number
with absolute
ODT numbers
Transmission type: “relative ODT numbers and absolute DAQ lists numbers”
In this case, both the DAQ lists number and the ODT number can be transmitted in the Identi-
fication Field. However, there is still space left over in the number of bytes that is available for
the information:
Identification Field
PID DAQ
Figure 31:
ID field with
absolute DAQ List number
relative ODT and
relative ODT number
absolute DAQ
numbers (one byte)
In the figure, one byte is available for the DAQ number and one byte for the ODT number.
The maximum number of DAQ lists can be transmitted using two bytes:
Identification Field
PID
DAQ
Figure 32:
ID field with
absolute DAQ list number
relative ODT and
relative ODT number
absolute DAQ
numbers (two bytes)
44
1 Fundamentals of the XCP protocol
If it is not possible to send three bytes, it is also possible to work with four bytes by using a fill
byte:
Identification Field
PID FILL
DAQ
Figure 33:
absolute DAQ list number
ID field with relative
for alignement
ODT and absolute DAQ
numbers as well as fill
relative ODT number
byte (total of four bytes)
How does the XCP Master now learn which method the Slave is using? First, by the entry in the
A2L and second by the request to the Slave to determine which communication version it has
implemented.
The response to the GET_DAQ_PROCESSOR_INFO request also sets the DAQ_KEY_BYTE that the
Slave uses to inform the Master which transmission type is being used. If not only DAQ is being
used, but also STIM, the Master must use the same method for STIM that the Slave uses for DAQ.
1.3.5 Bypassing = DAQ + STIM
Bypassing can be implemented by joint use of DAQ and STIM (see Figure 8) and it represents
a special form of a rapid prototyping solution. For a deeper understanding, however, further
details are necessary, so this method is not explained until chapter 4.5 “Bypassing”.
1.4 XCP Transport Layers
45
1.4 XCP Transport Layers
A main requirement in designing the protocol was that it must support different transport lay-
ers. At the time this document was defined, the following layers had been defined: XCP on CAN,
FlexRay, Ethernet, SxI and USB. The bus systems CAN, LIN and FlexRay are explained on the
Vector E-Learning platform, as well as an introduction to AUTOSAR. For details see the website
www.vector-elearning.com.
1.4.1 CAN
XCP was developed as a successor protocol of the CAN Calibration Protocols (CCP) and must
therefore absolutely satisfy the requirements of the CAN bus. The communication over the CAN
bus is defined by the associated description file. Usually the DBC format is used, but in some
isolated cases the AUTOSAR format ARXML is already being used.
A CAN message is identified by a unique CAN identifier. The communication matrix is defined in
the description file: Who sends which message and how are the eight useful bytes of the CAN bus
being used? The following figure illustrates the process:
Data
CAN
CAN
CAN
CAN
Frame
Node A
Node B
Node C
Node D
ID=0x12
Sender
Receiver
ID=0x34
Sender
Receiver
Receiver
ID=0x52
Receiver
Sender
ID=0x67
Receiver
Receiver
Sender
Receiver
ID=0xB4
Receiver
Sender
Figure 34:
Definition of which
ID=0x3A5
Sender
Receiver
Receiver
Receiver
bus nodes send
which messages
The message with ID 0x12 is sent by CAN node A and all other nodes on the bus receive this mes-
sage. In the framework of acceptance testing, CAN nodes C and D conclude that they do not
need the message and they reject it. CAN node B, on the other hand, determines that its higher-
level layers need the message and they provide them via the Rx buffer. The CAN nodes are inter-
linked as follows:
46
1 Fundamentals of the XCP protocol
CAN Node A
CAN Node B
Host
Host
CAN Interface
CAN Interface
Tx
Rx
Tx
Rx
Buffer
Buffer
Buffer
Buffer
Acceptance
Acceptance
Test
Test
Send
Receive
Send
Receive
CAN
Receive
Send
Receive
Send
Acceptance
Acceptance
Test
Test
Rx
Tx
Rx
Tx
Buffer
Buffer
Buffer
Buffer
CAN Interface
CAN Interface
Host
Host
Figure 35:
Representation
CAN Node C
CAN Node D
of a CAN network
The XCP messages are not described in the communication matrix! If measured values are sent
from the Slave via dynamic DAQ lists, e.g. with the help of XCP, the messages are assembled
according to the signals selected by the user. If the signal selection changes, the message con-
tents change as well. Nonetheless, there is a relationship between the communication matrix
and XCP: CAN identifiers are needed to transmit the XCP messages over CAN. To minimize the
number of CAN identifiers used, the XCP communication is limited to the use of just two CAN
identifiers that are not being used in the DBC for “normal” communication. One identifier is
needed to send information from the Master to the Slave; the other is used by the Slave for the
response to the Master.
The excerpt from the CANape Trace window shows the CAN identifiers that are used under the
“ID” column. In this example, just two different identifiers are used: 554 as the ID for the mes-
sage from Master to Slave (direction Tx) and 555 for sending messages from the Slave to the
Master (direction Rx).
1.4 XCP Transport Layers
47
Figure 36: Example of XCP-on-CAN communication
In this example, the entire XCP communication is handled by the two CAN identifiers 554 and
555. These two IDs may not be allocated for other purposes in this network.
The CAN bus transmits a maximum of eight useful bytes per message. In the case of XCP, how-
ever, we need information on the command used or the sent response. This is provided in the
first byte of the CAN useful data. This means that seven bytes are available per CAN message for
transporting useful data.
XCP on CAN Message (Frame)
XCP Packet
XCP Tail
XCP Header
empty for CAN PID FILL DAQ
TIMESTAMP
DATA
Fill
Control Field
Control Field
empty for CAN
for CAN
Figure 37: Representation of an XCP-on-CAN message
In CANape, you will find an XCP-on-CAN demo with the virtual ECU XCPsim. You can learn about
more details of the standard in ASAM XCP on CAN Part 3 Transport Layer Specification.
48
1 Fundamentals of the XCP protocol
1.4.2 CAN FD
CAN FD (CAN with flexible data rate) is an extension of the CAN protocol developed by
Robert Bosch GmbH. Its primary difference to CAN involves extending the useful data from 8 to
64 bytes. CAN FD also offers the option of sending the useful data at a higher data rate. After
the arbitration phase, the data bytes are sent at a higher transmission rate than during the
arbitration phase. This covers the need for greater bandwidth in automotive networks while pre-
serving valuable experience gained from CAN development.
The XCP-on-CAN-FD specification was defined in the XCP-on-CAN description of the XCP stan-
dard, Version 1.2.0 (June 2013).
Figure 38: Illustration of a CAN FD frame
Despite the largely similar modes of operation, this protocol requires extensions and modifica-
tions to the hardware and software. Among other things, CAN FD introduces three new bits to
the control field:
> Extended Data Length (EDL)
> Bit Rate Switch (BRS)
> Error State Indicator (ESI)
1.4 XCP Transport Layers
49
A recessive EDL bit (High level) distinguishes frames in extended CAN-FD format from those in
standard CAN format, because they are identified by a dominant EDL bit (low level). Similarly, a
recessive BRS bit causes the transmission of the data field to be switched to the higher bit rate.
The ESI bit identifies the error state of a CAN FD node. Another four bits make up what is known
as the Data Length Code (DLC), which represents the extended useful data length as a possible
value of 12, 16, 20, 24, 32, 48 and 64 bytes.
The use of XCP on CAN FD assumes that a second transmission rate has been defined for the use-
ful data in the A2L file. This is fully transparent to the user, who gets a complete A2L parameter-
ization. A measurement configuration in the XCP master considers the maximum packet length,
and the user does not need to make any other settings.
CAN FD is supported in CANape, Version 12.0 and higher. Every CAN hardware product from
Vector which begins with “VN” supports the CAN FD transport protocol.
50
1 Fundamentals of the XCP protocol
1.4.3 FlexRay
A basic idea in the development of FlexRay was to implement a redundant system with deter-
ministic time behavior. The connection redundancy was achieved by using two channels: chan-
nel A and channel B. If multiple FlexRay nodes (= ECUs) are redundantly interconnected and
one branch fails, the nodes can switch over to the other channel to make use of the connection
redundancy.
Node K
Node L
Node M
Node N
Node O
CH A
CH B
Figure 39: Nodes K and L are redundantly interconnected
Deterministic behavior is achieved by transmitting data within defined time slots. Also defined
here is which node sends which content in which time slot. These time slots are combined to
form one cycle. The cycles repeat here, as long as the bus is active. The assembly of the time
slots and their transport contents (who sends what at which time) is known as Scheduling.
Node K
Node L
Node M
Slot
Direction Frame
Slot
Direction Frame
Slot
Direction Frame
1
Tx
a
1
Tx
a
1
Tx
a
3
Rx
x
3
Rx
b
3
Rx
x
Frame: a
Frame: b
Frame: x
Frame: a
Frame: b
Frame: x
Slot 1
Slot 2
Slot 3
Slot 1
Slot 2
... Real-time
t1
t2
t3
t4
t5
t6
Communication Cycle
Next Communication Cycle
Figure 40: Communication by slot definition
1.4 XCP Transport Layers
51
In the first communication cycle, node K sends frame a in slot 1. The scheduling is also stored in
the software of nodes L and M. Therefore, the contents of frame a are passed to the next higher
communication levels.
Scheduling is consolidated in a description file. This is not a DBC file, as in the case of CAN,
rather it is a FIBEX file. FIBEX stands for “Field Bus Exchange Format” and could also be used
for other bus systems. However, its current use is practically restricted to the description of the
FlexRay bus. FIBEX is an XML format and the XCP-on-FlexRay specification relates to FIBEX Ver-
sion 1.1.5 and FlexRay specification Version 2.1.
Cycles
Slot
ECU
Channel
0
1
2
3
4
5
6
...
63
A
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
1
Node K
B
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
b [rep : 1 ]
A
c [rep : 4 ]
x [rep : 2 ]
y [rep : 4 ]
x [rep : 2 ]
c [ c
rep : 4 ]
x [rep : 2 ]
y [rep : 4 ]
x [rep : 2 ]
2
Node M
B
A
a [rep : 1 ]
a [rep : 1 ]
a [rep : 1 ]
a [rep : 1 ]
a [rep : 1 ]
a [rep : 1 ]
a [rep : 1 ]
Static Segment
a [rep : 1 ]
3
Node L
B
d [rep : 1 ]
d [rep : 1 ]
d [rep : 1 ]
d [rep : 1 ]
d [rep : 1 ]
d [rep : 1 ]
d [rep : 1 ]
d [rep : 1 ]
Node L
A
n [rep : 1 ]
n [rep : 1 ]
n [rep : 1 ]
n [rep : 1 ]
n [rep : 1 ]
n [rep : 1 ]
n [rep : 1 ]
n [rep : 1 ]
4
Node O
B
m [rep : 1 ]
m [rep : 1 ]
m [rep : 1 ]
m [rep : 1 ]
m [rep : 1 ]
m [rep : 1 ]
m [rep : 1 ]
m [rep : 1 ]
Node N
A
r [rep : 1 ]
r [rep : 1 ]
r [rep : 1 ]
r [rep : 1 ]
r [rep : 1 ]
r [rep : 1 ]
r [rep : 1 ]
r [rep : 1 ]
5
B
A
6
Node K
B
o [rep : 1 ]
o [rep : 1 ]
o [rep : 1 ]
o [rep : 1 ]
o [rep : 1 ]
o [rep : 1 ]
o [rep : 1 ]
o [rep : 1 ]
Node M
A
t [rep : 2 ]
p [rep : 4 ]
t [rep : 2 ]
t [rep : 2 ]
p [rep : 4 ]
t [r
ep : 2 ]
B
Dynamic Segment
Node L
A
u [rep : 4 ]
u [rep : 4 ]
7
Node L
B
v [rep : 8 ]
A
Node O
B
w [rep : 4 ]
w [rep : 4 ]
Figure 41: Representation of a FlexRay communication matrix
Another format for describing bus communication has been defined as a result of the develop-
ment of AUTOSAR solutions: the AUTOSAR Description File, which is available in XML format. The
definition of XCP-on-FlexRay was taken into account in the AUTOSAR 4.0 specification. However,
at the time of publication of this book this specification has not yet been officially approved and
therefore it will not be discussed further.
Due to other properties of the FlexRay bus, it is not sufficient to just give the slot number as
a reference to the contents. One reason is that multiplexing is supported: whenever a cycle is
repeated, the transmitted contents are not necessarily the same. Multiplexing might specify
that a certain piece of information is only sent in the slot in every second pass.
52
1 Fundamentals of the XCP protocol
Instead of indicating the pure slot number, “FlexRay Data Link Layer Protocol Data Unit Identi-
fiers” (FLX_LPDU_ID) are used, which can be understood as a type of generalized Slot ID. Four
pieces of information are needed to describe such an LPDU:
> FlexRay Slot Identifier (FLX_SLOT_ID)
> Cycle Counter Offset (OFFSET)
> Cycle Counter Repetition (CYCLE_REPETITION)
> FlexRay Channel (FLX_CHANNEL)
LPDU_ID
...
Channel A
... ...
Channel B
Cycle ID . . . . . . . . . . . . . ...
.
. . . . .
. .. .. .. .. .. .. .. .. ..
.. .. .. .. ..
.. . . . . . . . . . . . . . . . . .
. .. .. .. .. .. .. .. .. ..
.
...
. .. .. .. ..
... ...
... ...
...
Figure 42:
Representation of
Slot ID
the FlexRay LPDUs
Scheduling also has effects on the use of XCP on FlexRay, because it defines what is sent pre-
cisely. This cannot be readily defined in XCP; not until the measurement runtime does the user
define which measured values are sent by assembling signals. This means that it is only possible
to choose which aspect of XCP communication can be used in which LPDU: CTO or DTO from Mas-
ter to Slave or from Slave to Master.
The following example illustrates this process: the XCP Master may send a command (CMD) in
slot n and Slave A gives the response (RES) in slot n + 2. XCP-on-FlexRay messages are always
defined using LPDUs.
The A2L description file is needed for access to internal ECU parameters; the objects with their
addresses in the ECU are defined in this file. In addition, the FIBEX file is necessary, so that
the XCP Master knows which LPDUs it may send and to which LPDUs the XCP Slaves send their
responses. Communication between XCP Master and XCP Slave(s) can only function through
combination of the two files, i.e. by having an A2L file reference a FIBEX file.
1.4 XCP Transport Layers
53
Excerpt of an A2L with XCP-on-FlexRay parameter setting:
…
/begin XCP_ON_FLX
…
„XCPsim.xml“
„Cluster_1“
…
In this example, “XCPsim.xml” is the reference from the A2L file to the FIBEX file.
XCP-dedicated LPDU_IDs
...
Channel A
... ...
Channel B
Cycle ID . . . . . . . . . . . . . ...
.
. . . . .
. .. . .
. . .. . .
. . .. .. ..
.. .. .. .. ..
.. . . . . . . . . . . . . . . . . .
. .. .. .. .. .. .. .. .. ..
.
...
. .. .. .. ..
... ...
... ...
Figure 43:
...
Allocation of
XCP communication
Slot ID
to LPDUs
You can read more details about XCP on FlexRay in CANape’s online Help. Supplied with CANape
is the FIBEX Viewer, which lets users conveniently view the scheduling. It is easy to allocate the
XCP messages to the LPDUs by making driver settings for the XCP-on-FlexRay device in CANape.
The protocol is explained in detail in ASAM XCP on FlexRay Part 3 Transport Layer Specification.
You will find an XCP-on-FlexRay demo in CANape with the virtual ECU XCPsim. The demo requires
real Vector FlexRay hardware.
1.4.4 Ethernet
XCP on Ethernet can be used with either TCP/IP or UDP/IP. TCP is a protected transport protocol
on Ethernet, in which the handshake method is used to detect any loss of a packet. In case of
packet loss, TCP organizes a repetition of the packet. UDP does not offer this protection mech-
anism. If a packet is lost, UDP does not offer any mechanisms for repeated sending of the lost
packet on the protocol level.
Not only can XCP on Ethernet be used with real ECUs, it can also be used for measurement and
calibration of virtual ECUs. Here, a virtual ECU is understood as the use of code that would other-
wise run in the ECU as an executable program (e.g. DLL) on the PC. Entirely different resources
are available here compared to an ECU (CPU, memory, etc.).
54
1 Fundamentals of the XCP protocol
But first the actual protocol will be discussed. IP packets always contain the addresses of the
sender and receiver. The simplest way to visualize an IP packet is as a type of letter that contains
the addresses of the recipient and the sender. The addresses of individual nodes must always be
unique. A unique address comprises the IP address and port number.
XCP on Ethernet (TCP/IP and UDP/IP) Message (Frame)
XCP Header
XCP Packet
XCP Tail
empty for Ethernet
LEN
CTR
(TCP/IP and UDP/IP)
PID FILL DAQ
TIMESTAMP
DATA
Control Field
Length (LEN)
Control Field
for Ethernet
empty for Ethernet
(TCP/ IP and UDP/IP)
(TCP&IP and UDP&IP)
Figure 44: XCP packet with TCP/IP or UDP/IP
The header consists of a Control Field with two words in Intel format (= four bytes). These words
contain the length (LEN) and a counter (CTR). LEN indicates the number of bytes in the XCP
packet. The CTR is used to detect the packet loss. UDP/IP is not a protected protocol. If a packet
is lost, this is not recognized by the protocol layer. Packet loss is monitored by counter infor-
mation. When the Master sends its first message to the Slave, it generates a counter number
that is incremented with each additional transmission of a frame. The Slave responds with the
same pattern: It increments its own counter with each frame that it sends. The counters of the
Slave and the Master operate independently of one another. UDP/IP is well suited for sending
measured values. If a packet is lost, then the measured values it contains are lost, resulting in
a measurement gap. If this occurs infrequently, the loss might just be ignored. But if the mea-
sured data is to be used as the basis for fast control, it might be advisable to use TCP/IP.
An Ethernet packet can transport multiple XCP packets, but an XCP packet may never exceed the
limits of a UDP/IP packet. In the case of XCP on Ethernet, there is no “Tail”, i.e. an empty con-
trol field.
You will find more detailed information on the protocol in ASAM XCP on Ethernet Part 3 Trans-
port Layer Specification. In CANape, you will also find an XCP on Ethernet demo with the virtual
ECU XCPsim or with virtual ECUs in the form of DLLs, which have been implemented by Simulink
models and the Simulink Coder.
1.4 XCP Transport Layers
55
1.4.5 SxI
SxI is a collective term for SPI or SCI. Since they are not buses, but instead are controller inter-
faces which are only suited for point-to-point connections, there is no addressing in this type
of transmission. The communication between any two nodes runs either synchronously or
asynchronously.
XCP on Sxl Message (Frame)
XCP Header
XCP Packet
XCP Tail
LEN
CTR
PID FILL
DAQ
TIMESTAMP
DATA
FILL
CS
Control Field
Length (LEN)
Control Field
for SxI
for SxI
Checksum (CS)
Figure 45: XCP-on-SxI packet
The XCP header consists of a control field with two pieces of information: the length LEN and
the counter. The length of these parameters may be in bytes or words (Intel format). LEN indi-
cates the number of bytes of the XCP packet. The CTR is used to detect the loss of a packet. This
is monitored in the same way as for XCP on Ethernet: with counter information. Under certain
circumstances it may be necessary to add fill bytes to the packet, e.g. if SPI is used in WORD or
DWORD mode or to avoid the message being shorter than the minimal packet length. These fill
bytes are appended in the control field.
You will find more detailed information on the protocol in ASAM XCP on SxI Part 3 Transport
Layer Specification.
1.4.6 USB
Currently, XCP on USB has no practical significance. Therefore, no further mention will be made
of this topic; rather we refer you to ASAM documents that describe the standard: ASAM XCP on
USB Part 3 Transport Layer Specification.
1.4.7 LIN
At this time, ASAM has not yet defined an XCP-on-LIN standard. However, a solution exists from
Vector (XCP-on-LIN driver and CANape as XCP-on-LIN Master), which violates neither the LIN nor
the XCP specification and is already being used on some customer projects. For more detailed
information, please contact Vector.
56
1 Fundamentals of the XCP protocol
1.5 XCP Services
This chapter contains a listing and explanation of other services that can be realized over XCP.
They are all based on the already described mechanisms of communication with the help of CTOs
and DTOs. Some XCP services have already been explained, e.g. synchronous data acquisition/
stimulation and read/write access to device memory.
The XCP specification does indeed uniquely define the different services; at the same time it
indicates whether the service always needs to be implemented or whether it is optional. For
example, an XCP Slave must support “Connect” for the Master to set up a connection. On the
other hand, flashing over XCP is not absolutely necessary and the XCP Slave does not need to
support it. This simply depends on the requirements of the project and the software. All of the
services described in this chapter are optional.
1.5.1 Memory Page Swapping
As already explained in the description of calibration concepts, parameters are normally located
in flash memory and are copied to RAM as necessary. Some calibration concepts offer the option
of swapping memory segment pages from RAM and Flash. XCP describes a somewhat more gen-
eral, generic approach, in which a memory segment may contain multiple swappable pages.
Normally, this consists of a RAM page and a flash page. But multiple RAM pages or the lack of a
flash page are conceivable as well.
For a better understanding of the XCP commands for page swapping, the concepts of sector, seg-
ment and page will be explained once again at this point.
XCP access
Segment 1
Segment 1
Segment 1
2
Page 0
Page 1
Page 2
Segmemt 1
Sector
ECU access
Segment 0
Page 0
1
Segmemt 0
Sector
0
Figure 46:
Sector
address
Memory
representation
1.5 XCP Services
57
From an XCP perspective, the memory of a Slave consists of a continuous memory that is
addressed with a 40-bit width. The physical layout of the memory is based on sectors. Know-
ledge of the flash sectors is absolutely necessary in flashing, because the flash memory can only
be erased a block at a time.
The logical structure is based on what are known as segments; they describe where calibration
data is located in memory. The start address and parameters of a segment do not have to be
aligned with the start addresses and parameters of the physical sectors. Each segment can be
subdivided into multiple pages. The pages of a segment describe the same parameters at the
same addresses. The values of these parameters and read/write rights can be controlled indi-
vidually for each page.
The allocation of an algorithm to a page within a segment must always be unique. Only one page
may be active in a segment at any given time. This page is known as the “active page for the
ECU in this segment.” The particular page that the ECU and the XCP driver actively access can be
individually switched. No interdependency exists between these settings. Similar to the nam-
ing convention for the ECU, the active page for XCP access is referred to as the “active page for
XCP access in this segment”.
In turn, this applies to each individual segment. Segments must be listed in the A2L file and
each segment gets a number that is used to reference the segment. Within an XCP Slave, the
SEGMENT_NUMBER must always begin at 0 and it is then incremented in consecutive numbers.
Each segment has at least one page. The pages are also referenced by numbers. The first page
is PAGE 0. One byte is available for the number, so that a maximum of 255 pages can be defined
per segment.
The Slave must initialize all pages for all segments. The master uses the command GET_CAL_PAGE
to ask the Slave which page is currently active for the ECU and which page for XCP access. It
can certainly be the case that mutual blocking may be necessary for the accesses. For exam-
ple, the XCP Slave may not access a page, if this page is currently active for the ECU. As men-
tioned, there may be a dependency – but not necessarily. It is a question of how the Slave has
been implemented.
If the Slave supports the optional commands GET_CAL_PAGE and SET_CAL_PAGE, then it also
supports what is known as page swapping. These two commands let the Master poll which pages
are currently being used and if necessary it can swap pages for the ECU and XCP access. The XCP
Master has full control over swapping of pages. The XCP Slave cannot initiate swapping by itself.
But naturally the Master must respect any restrictions of the Slave implementation.
What is the benefit of swapping?
First, swapping permits very quick changing of entire parameter sets – essentially a before-and-
after comparison. Second, the plant remains in a stable state, while the calibrator performs
extensive parameter changes on another page in the ECU. This prevents the plant from going
into a critical or unstable state, e.g. due to incomplete datasets during parameter setting.
58
1 Fundamentals of the XCP protocol
1.5.2 Saving Memory Pages – Data Page Freezing
When a calibrator calibrates parameters on a page, there is the conceptual ability in XCP to save
the data directly in the ECU. This involves saving the data of a RAM page to a page in nonvola-
tile memory. If the nonvolatile memory is flash, it must be taken into account that the segment
start address and the segment size might not necessarily agree with the flash sectors, which
represents a problem in erasing and rewriting the flash memory (see ASAM XCP Part 2 Protocol
Layer Specification).
1.5.3 Flash Programming
Flashing means writing data in an area of flash memory. This requires precise knowledge of how
the memory is laid out. A flash memory is subdivided into multiple sectors (physical sections),
which are described by a start address and a length. To distinguish them from one another, they
each get a consecutive identification number. One byte is available for this number, resulting in
a maximum of 255 sectors.
SECTOR_NUMBER [0, 1, 2 … 255]
The information about the flash sectors is also part of the A2L data set.
Figure 47:
Representation
of driver settings
for the flash area
1.5 XCP Services
59
Flashing can be implemented using what are referred to as “flash kernels”. A flash kernel is exe-
cutable code that is sent to the Slave’s RAM area before the actual flashing; the kernel then han-
dles communication with the XCP Master. It might contain the algorithm that is responsible for
erasing the flash memory. For security and space reasons, very frequently this code is not per-
manently stored in the ECU’s flash memory. Under some circumstances, a converter might be
used, e.g. if checksum or similar computations need to be performed.
Flashing with XCP roughly subdivides the overall flash process into three areas:
> Preparation (e.g. for version control and therefore to check whether the new contents
can even be flashed)
> Execution (the new contents are sent to the ECU)
> Post-processing (e.g. checksum checking etc.)
In the XCP standard, the primary focus is directed to the actual execution of flashing. Any-
one who compares this operation to flashing over diagnostic protocols will discover that the
process-specific elements, such as serial number handling with meta-data, are supported in
a rather spartan fashion in XCP. Flashing in the development phase was clearly the main focus
in its definition and not the complex process steps that are necessary in end-of-line flashing.
Therefore, what is important in the preparation phase is to determine whether the new con-
tents are even relevant to the ECU. There are no special commands for version control. Rather
the practice has been to support those commands specific to the project.
The following XCP commands are available:
PROGRAM_START: Beginning of the flash procedure
This command indicates the beginning of the flash process. If the ECU is in a state that does not
permit flashing (e.g. vehicle speed > 0), the XCP Slave must acknowledge with an ERRor. The
actual flash process may not begin until the PROGRAM_START has been successfully acknowl-
edged by the Slave.
PROGRAM_CLEAR: Call the current flash memory erasing routine
Before flash memory can be overwritten with new contents, it must first be cleared. The call of
the erasing routine via this command must be implemented in the ECU or be made available to
the ECU with the help of the flash kernel.
PROGRAM_FORMAT: Select the data format for the flash data
The XCP Master uses this command to define the format (e.g. compressed or encrypted) in which
the data are transmitted to the Slave. If the command is not sent, the default setting is non-
compressed and non-encrypted transmission.
PROGRAM: Transfer the data to the XCP Slave
For the users who are very familiar with flashing via diagnostics: this command corresponds to
TRANSFERDATA in diagnostics. Using this command, data is transmitted to the XCP Slave, which
is then stored in flash memory.
60
1 Fundamentals of the XCP protocol
PROGRAM_VERIFY: Request to check the new flash contents
The Master can request that the Slave perform an internal check to determine whether the new
contents are OK.
PROGRAM_RESET: Reset request to the Slave
Request by the Master to the Slave to execute a Reset. Afterwards, the connection to the Slave
is always terminated and a new CONNECT must be sent.
1.5.4 Automatic Detection of the Slave
The XCP protocol lets the Master poll the Slave about its protocol-specific properties. A number
of commands are available for this.
GET_COMM_MODE_INFO
The response to this command gives the Master information about the various communication
options of the Slave, e.g. whether it supports block transfer or interleaved mode or which mini-
mum time intervals the Master must maintain between Requests in these modes.
GET_STATUS
The response to this request returns all current status information of the Slave. Which resources
(calibration, flashing, measurement, etc.) are supported? Are any types of memory activities
(DAQ list configuration, etc.) still running currently? Are DTOs (DAQ, STIM) being exchanged
right now?
GET_DAQ_PROCESSOR_INFO
The Master gets general information, which it needs to know about the Slave limitations: num-
ber of predefined DAQ lists, available DAQ lists and events, etc.
GET_DAQ_RESOLUTION_INFO
Other information about the DAQ capabilities of the Slave is exchanged via this command: max-
imum number of parameters for an ODT for DAQ and for STIM, granularity of the ODT entries,
number of bytes in time stamp transmission, etc.
GET_DAQ_EVENT_INFO
When this command is used, the call is made once per ECU event. Information is transmitted
here on whether the event can be used for DAQ, STIM or DAQ/STIM, whether the event occurs
periodically and if so which cycle time it has, etc.
1.5 XCP Services
61
1.5.5 Block Transfer Mode for Upload, Download and Flashing
In the “normal” communication mode, each command from the Master is acknowledged by a
response of the Slave. However, in some cases it may be desirable, for performance reasons, to
use what is referred to as the block transfer mode.
Master
Slave
Request k
Part1
Part2
MIN_ST
Part3
MAX_BS
Response k
Request k+1
Figure 48:
Representation
Time
of the block
transfer mode
The use of such a method accelerates the procedure when transmitting large amounts of data
(UPLOAD, SHORT_UPLOAD, DOWNLOAD, SHORT_DOWNLOAD and PROGRAM). The Master can find
out whether the Slave supports this method with the request GET_COMM_MODE_INFO. You will
find more on this in ASAM XCP Part 2 Protocol Layer Specification.
62
1 Fundamentals of the XCP protocol
1.5.6 Cold Start Measurement (start of measurement during power-on)
Even with the capabilities of XCP described to this point, it would be impossible to implement
an event-driven measurement that can in practice be executed early in the ECU’s start phase.
The reason is that the measurement must be configured before the actual measurement takes
place. If one attempts to do this, the ECU’s start phase has long been over by the time the first
measured values are transmitted. The approach that is used to overcome this problem is based
on a simple idea.
It involves separating the configuration and the measurement in time. After the configura-
tion phase, the measurement is not started immediately; rather the ECU is shut down. After a
reboot, the XCP Slave accesses the existing configuration directly and immediately begins to
send the first messages. The difficulties associated with this are obvious: the configuration of
the DAQ lists is stored in RAM, and therefore the information no longer exists after a reboot.
To enable what is known as the RESUME mode to enable a Cold Start Measurement, a nonvolatile
memory is needed in the XCP Slave which preserves its data even when it is not being supplied
with power. EEPROMs are used in this method. In this context, it is irrelevant whether it is a real
EEPROM or one that is emulated by a flash memory.
You will find more details in ASAM XCP Part 1 Overview Specification in the chapter 1.4.2.2
“Advanced Features”.
1.5 XCP Services
63
1.5.7 Security Mechanisms with XCP
An unauthorized user should be prevented as much as possible from being able to make a con-
nection to an ECU. The “seed & key” method is available for checking whether or not a connec-
tion attempt is authorized. The three different access types can be protected by seed & key:
measurement / stimulation, calibration and flashing.
The “seed & key” method operates as follows: in the connect request by the Master, the Slave
sends a random number (= seed) to the Master. Now, the Master must use an algorithm to gen-
erate a response (= key). The key is sent to the Slave. The Slave also computes the expected
response and compares the key of the Master with its own result. If the two results agree, both
the Master and Slave have used the same algorithm. Then the Slave accepts the connection to
the Master. If there is no agreement, the Slave declines communication with the Master.
Normally, the algorithm is available as a DLL in the Master. So, if a user has the “seed & key”
DLL and the A2L file, nothing stands in the way of accessing the ECU’s memory. When the ECU
is approaching a production launch, the XCP driver is often deactivated. A unique sequence of
individual diagnostic commands is usually used to restore XCP access to the ECU. This makes
the XCP driver largely available even in production vehicles, but it is normally deactivated to
protect against unauthorized manipulation of the ECU (see ASAM XCP Part 2 Protocol Layer
Specification).
Whether or not seed & key or deactivation of the XCP driver is used in a project is implementa-
tion-specific and independent of the XCP specification.
64
2 ECU Description File A2L
65
2 ECU Description File A2L
66
2 ECU Description File A2L
One reason why an A2L file is needed has already been named: to allocate symbolic names to
addresses. For example, if a software developer has implemented a PID controller and assigned
the names P1, I1 and D1 in his application for the proportional, integral and differential compo-
nents, then the calibrator should be able to access these parameters with their symbolic names.
Let us take the following figure as an example:
Figure 49:
Parameters in
a calibration window
The user can conveniently modify values using symbolic names. Another example is provided by
viewing signal variables that are measured from the ECU:
Figure 50: Signal response over time
In the legend, the user can read the logical names of the signals. The addresses at which the
parameters were located in the ECU are of secondary importance in the offline analysis of val-
ues. Naturally, the correct address is needed to request the values in the ECU, but the numeric
value of the address itself is of no importance to the user. The user uses the logical name for
selection and visualization purposes. That is, the user selects the object by its name and the XCP
Master looks for the associated address and data type in the A2L.
2 ECU Description File A2L
67
Another attribute of a parameter might be the definition of a minimum or maximum value. The
value of the object would then have to lie within these limits. Imagine that you as the software
developer define a parameter that has a direct effect on a power output stage. You must now
prevent the user – whatever the user’s reasons might be – from configuring the output stage
that would result in catastrophic damage. You can accomplish this by defining minimum and
maximum values in the A2L to limit the permitted values.
Rules for conversion between physical and raw values are also defined in the A2L. You can visu-
alize a simple example of such a conversion rule in a sensor that has an 8-bit value. The numeric
values output by the sensor lie between 0 and 255, but you wish to see the value as a percent-
age value. Mapping of the sensor value [0 … 255] to [0 … 100 %] is performed with a conver-
sion rule, which in turn is stored in the A2L. If an object is measured, which exists as a raw value
in the ECU and is also transmitted as such, the measurement and calibration tool uses the stored
formula and visualizes the physical value.
Besides scalar parameters, characteristic curves and maps are frequently used. Some might uti-
lize a proximity sensor such as a Hall sensor, which determines distance as a function of mag-
netic field strength and you may wish to use this distance value in your algorithm. The magnetic
field and distance value do not run linear to one another. This nonlinearity of values would make
formulation of the algorithm unnecessarily difficult. With the help of a characteristic curve, you
can first linearize the values before you input the values into your algorithm as input variables.
Another application area for characteristic maps is their use as substitutes for complex compu-
tations. For example, if there is a relationship y = f(x) and the function f is associated with a lot
of computing effort, it is often simpler to simply compute the values over the potential range of
x in advance and store the results in the form of a table (= characteristic curve). If the value x
is now in the ECU, the value y does not need to be computed at the controller’s runtime, rather
the map returns the result y to the input variable x. It may be necessary to interpolate between
two values, but that would be the extent of the calculations.
How is this characteristic curve stored in memory? Are all x values input first and then all y val-
ues? Or does storage follow the pattern: x1, y1; x2, y2; x3, y3 …? Since various options are
available, the type of memory storage is defined in a storage scheme in the A2L.
The convenience for the user comes from the ability to work with symbolic names for parame-
ters, the direct look at the physical values and access to complex elements such as characteris-
tic maps, without having to concern oneself with complex storage schemes.
Another advantage is offered by the communication parameters. They are also defined in the
A2L. In the communication between the measurement and calibration tool and the ECU, the
parameter set from the A2L is used. The A2L contains everything that the measurement and cal-
ibration tool needs to communicate with the ECU.
68
2 ECU Description File A2L
2.1 Setting Up an A2L File for an XCP Slave
The A2L file is an ASCII-readable file, which describes the following with the help of keywords:
> Interface-specific parameters between measurement and calibration tool and A2L file (the
description is located at the beginning of the A2L file and is located in what is referred to as
the AML tree),
> Communication to the ECU,
> Storage scheme for characteristic curves and maps (keyword RECORD_LAYOUT),
> Conversion rules for converting raw values to physical values (keyword COMPU_METHOD),
> Measurement parameters (keyword MEASUREMENT),
> Calibration parameters (keyword CHARACTERISTIC) and
> Events that are relevant for triggering a measurement keyword EVENT),
A summary of parameters and measurement parameters is made with the help of groups (keyword
GROUP).
Example of a measurement parameter with the name “Shifter_B3”:
/begin MEASUREMENT Shifter_B3 “Single bit signal (bit from a byte shifting)”
UBYTE HighLow 0 0 0 1
READ_WRITE
BIT_MASK 0x8
BYTE_ORDER MSB_LAST
ECU_ADDRESS 0x124C02
ECU_ADDRESS_EXTENSION 0x0
FORMAT “%.3”
/begin IF_DATA CANAPE_EXT
100
LINK_MAP “byteShift” 0x124C02 0x0 0 0x0 1 0x87 0x0
DISPLAY 0 0 20
/end IF_DATA
/end MEASUREMENT
Example of a parameter map with the name KF1:
/begin CHARACTERISTIC KF1 “8*8 BYTE no axis”
MAP 0xE0338 __UBYTE_Z 0 Factor100 0 2.55
ECU_ADDRESS_EXTENSION 0x0
EXTENDED_LIMITS 0 2.55
BYTE_ORDER MSB_LAST
BIT_MASK 0xFF
/begin AXIS_DESCR
FIX_AXIS NO_INPUT_QUANTITY BitSlice.CONVERSION 8 0 7
EXTENDED_LIMITS 0 7
READ_ONLY
BYTE_ORDER MSB_LAST
FORMAT “%.0”
2.2 Manually Creating an A2L File
69
FIX_AXIS_PAR_DIST 0 1 8
/end AXIS_DESCR
/begin AXIS_DESCR
FIX_AXIS NO_INPUT_QUANTITY BitSlice.CONVERSION 8 0 7
EXTENDED_LIMITS 0 7
READ_ONLY
BYTE_ORDER MSB_LAST
FORMAT “%.0”
FIX_AXIS_PAR_DIST 0 1 8
/end AXIS_DESCR
/begin IF_DATA CANAPE_EXT
100
LINK_MAP “map3_8_8_uc” 0xE0338 0x0 0 0x0 1 0x87 0x0
DISPLAY 0 0 255
/end IF_DATA
FORMAT “%.3”
/end CHARACTERISTIC
The ASCII text is not easy to understand. You will find a description of its structure in ASAM XCP
Part 2 Protocol Layer Specification in chapter 2.
The sections below describe how to create an A2L. Let us focus on the actual contents of an A2L
and their meanings and leave the details of the A2L description language to an editor. The A2L
Editor that is supplied with CANape is used here.
2.2 Manually Creating an A2L File
The A2L mainly describes the contents of the memory of the XCP Slave. The contents depend on
the application in the Slave, which was developed as C code. After the compiler/linker run of
the application code, important elements of an A2L file already exist in the linker-map file: the
names of the objects, their data types and memory addresses. Still lacking are the parameters
for communication between XCP Master and Slave. Other information is usually needed such as
minimum and maximum values of parameters, conversion rules, storage schemes for character-
istic maps etc.
Let us begin by creating an empty A2L and the communication parameters: If you wish to cre-
ate an A2L that describes an ECU with an XCP-on-CAN interface, for example, you create a new
device in CANape and select XCP on CAN as the interface. Then you can supplement this with
other communication-specific information (e.g. CAN identifiers). After saving the file, you have
an A2L that contains the entire communication content of the A2L. Still lacking are the defini-
tions of the actual measurement and calibration parameters.
70
2 ECU Description File A2L
In the A2L Editor (available as part of CANape or as a separate tool), the linker-map file is asso-
ciated to the A2L. In a selection dialog, the user can now select those parameters from the map
file which it needs in the A2L: scalar measurement and calibration parameters, characteristic
curves and maps. The user can gradually add the desired parameters to the A2L step by step and
group them. Other object-specific information is also added using the editor.
What should be done when you modify your code, recompile it and link it? It is highly proba-
ble that the addresses of objects will change. Essentially, it is not necessary to generate a new
A2L. If you wish to have objects just added to the code also be available in the A2L, you must of
course add them to the A2L. Address updating is always necessary in the A2L. This is done with
the editor; it searches for the relevant entry in the linker-map file based on the name of the A2L
object, reads out the address and updates it in the A2L.
If your application changes very dynamically – objects are renamed, data types are adapted,
parameters are deleted and others added – then the manual work method is impractical. To gen-
erate an A2L from a C code, other tools are available for automatic processing.
On the Vector homepage you will find information on the “ASAP2 Tool-Set” with which you can
automate the generation of A2Ls from the source code in a batch process.
2.3 A2L Contents versus ECU Implementation
When an XCP Master tool reads in an A2L that does not fully match the ECU, misunderstandings
in the communication might occur. For example, another value related to time stamp resolution
might be in the A2L file that differs from the value implemented in the ECU. If this is the case,
the problem must be detected and solved. The user gets support from the Master, who can poll
the Slave via the protocol to determine what was really implemented in the Slave.
XCP offers a number of functions that were developed for automatic detection of the Slave. Of
course, this assumes that automatic detection is implemented in the Slave. If the Master polls
the Slave and the Slave’s responses do not agree with the parameter set of the A2L description
file, the Master must decide which settings to use. In CANape, the information that is read out
by the Slave is given a higher priority than the information from the A2L.
2.3 A2L Contents versus ECU Implementation
71
Here is an overview of possible commands that are used to find out something about the XCP
implementation in the Slave:
GET_DAQ_PROCESSOR_INFO
Returns general information on the DAQ lists: MAX_DAQ, MAX_EVENT_CHANNEL, MIN_DAQ
GET_DAQ_RESOLUTION_INFO
Maximum parameter of an ODT entry for DAQ/STIM, time interval information
GET_DAQ_EVENT_INFO (Event_channel_number)
Returns information for a specific time interval: Name and resolution of the time interval, num-
ber of DAQ lists that may be assigned to this time interval …
GET_DAQ_LIST_INFO (DAQ_List_Number)
Returns information on the selected DAQ list: MAX_ODT, MAX_ODT_ENTRIES exist as predefined
DAQ lists …
72
3 Calibration Concepts
73
3 Calibration Concepts
74
3 Calibration Concepts
ECU parameters are constant parameters that are adapted and optimized during the develop-
ment of the ECU or an ECU variant. This is an iterative process, in which the optimal value of a
parameter is found by repeated measurements and changes.
The calibration concept answers the question of how parameters in the ECU can be changed
during an ECU’s development and calibration phases. There is not one calibration concept that
exists, rather several. Which concept is utilized usually depends very much on the capabilities
and resources of the microcontroller that is used.
Normally, parameters are stored in the production ECU’s flash memory. The underlying program
variables are defined as constants in the software. To make parameters modifiable at runtime
during an ECU’s development, additional RAM memory is needed.
A calibration concept is concerned with such questions as these: How do the parameters initially
find their way from flash to RAM? How is the microcontroller’s access to RAM rerouted? What
does the solution look like when there are more parameters than can be simultaneously stored
in RAM? How are the parameters copied back into flash? Are changes to the parameters persis-
tent, i.e. are they preserved when the ECU is turned off?
A distinction is made between transparent and non-transparent calibration concepts. Transpar-
ent means that the calibration tool does not need to be concerned with the above questions,
because all necessary mechanisms are implemented in the ECU.
Several methods are briefly introduced in the following.
3.1 Parameters in Flash
The software developer defines in the source code whether a parameter is a variable or a con-
stant, i.e. whether a parameter is stored in flash or in RAM memory.
C code example:
const float factor = 0.5;
The “factor” parameter represents a constant with the value 0.5. During compiling and linking
of the code, memory space is provided in flash for the “factor” object. The object is allocated
an address that lies in the data area of the flash memory. The value 0.5 is found at the relevant
address in the hex file and the address appears in the linker-map file.
The simplest conceivable calibration concept involves modifying the value in C code, generating
a new hex file and flashing. However, this method is very laborious, because every value change
must be made in code, resulting in the need for a compiler/linker run with subsequent flashing.
An alternative approach would be to only modify the value in the hex file and then reflash this
file. Every calibration tool is capable of doing this. It is referred to as “offline calibration” of the
hex file, which is a very commonly used method.
3.1 Parameters in Flash
75
Under some circumstances, with certain compilers it may be necessary to explicitly ensure that
parameters are always also stored in flash memory and not integrated in the code, for exam-
ple and therefore do not appear at all in the linker-map file. Usually, one does not want to leave
to chance where a constant is created in flash memory. The necessary means for accomplish-
ing this are almost always compiler-specific pragma instructions. To prevent the compiler from
embedding them in the code, it is generally sufficient to use the “volatile” attribute for con-
stant parameters. A typical definition of a flash constant appears as in the following example:
C code example:
#pragma section “FLASH_Parameter”
volatile const float factor = 0.5;
It is normally not possible to calibrate parameters in flash online. Indeed, most microcontrollers
are able to program their flash themselves, which is necessary for the purposes of re-program-
ming in the field. Nonetheless, flash memory always has the property of being organized into
larger blocks (sectors), which can only be erased as a whole. It is practically impossible to flash
just individual parameters, because the ECU normally does not have the resources to buffer the
rest of the sector and reprogram it. In addition, this process would take too much time.
Some ECUs have the ability to store data in what is known as an EEPROM memory. In contrast to
flash memories, EEPROM memories can erase and program each memory cell individually. The
amount of available EEPROM memory is always considerably less than the available flash mem-
ory and it is usually limited to just a few kilobytes. EEPROM memory is often used to store pro-
grammable parameters in the service shop or to implement a persistence mechanism in the
ECU, e.g. for the odometer. Online calibration would be conceivable here, but it is seldom used,
because access to EEPROM cells is relatively slow and during the booting process EEPROM param-
eters are usually copied over to RAM memory, where it is possible to access them directly. ECUs
which have no EEPROM memory often implement what is known as an EEPROM emulation. In
this method, multiple small flash sectors are used in alternation to record parameter changes,
so that the last valid value can always be determined. Online calibration would also be conceiv-
able with this method.
In both cases, the relevant memory accesses would then be intercepted in the software com-
ponents of the XCP driver and implemented with the software routines of the EEPROM or the
EEPROM emulation. The Vector XCP Professional driver offers the software hooks needed for this.
76
3 Calibration Concepts
3.2 Parameters in RAM
The most frequently used approach to modifying parameters at runtime (“online calibration”) is
to create the parameters in the available RAM memory.
C code example:
#pragma section “RAM_Parameter”
volatile float factor = 0.5;
This defines the parameter “factor” as a RAM variable with the initial value 0.5. During compil-
ing and linking of the code, memory space is reserved for the object “factor” in RAM and the
associated RAM address appears in the linker-map file. The initial value 0.5 is stored in flash
memory and at the relevant location in the hex file. The addresses of the initial values in flash
memory are defined by parameterization of the linker, but they do not appear in the linker-map
file.
During booting of the ECU, all RAM variables are initialized once with their initial values from
flash memory. This is usually executed in the start-up code of the compiler producer and the
application programmer does not need to be concerned with it. The application uses the val-
ues of parameters located in RAM and they can be modified via normal XCP memory accesses.
From the perspective of the ECU software, calibration parameters in RAM are always still
unchangeable, i.e. the application itself does not change them. Many compilers discover this
fact by code analysis and simply optimize the necessary RAM memory space away. Normally,
it is therefore also necessary to prevent the compiler from optimizing by using the “volatile”
attribute.
From the perspective of the calibration tool, the RAM area in which the parameters are located
is referred to as calibration RAM (memory that can be calibrated).
FLASH
RAM
Calibration RAM
Figure 51:
Parameters
Initial parameter
setting in RAM
The calibration RAM does not need to consist of a fully contiguous RAM area. It may also be dis-
tributed into multiple areas or even in any desired way. Nonetheless, it offers significant advan-
tages for organizing the parameters in just a few contiguous RAM areas and isolating them from
other RAM parameters such as changing state variables and intermediate results. This is espe-
cially important if offline calibration of the calibration RAM with a hex file should be enabled.
At the user’s request, the calibration tool must be able to load the parameters that were mod-
ified offline into the ECU during the transition from offline calibration to online calibration.
3.2 Parameters in RAM
77
This case occurs very frequently. For example, when calibrators reconnect with their ECU on the
next work day, they want to resume work at the point at which they stopped the evening before.
However, booting of the ECU causes the flashed contents to be copied to the RAM as an initial
dataset. To let users resume with work accomplished on the previous day, the parameter set
file saved the previous evening in the ECU’s RAM must be loaded. This loading process may be
time optimized by limiting the number of necessary transmissions to a minimum. It is advanta-
geous here if the tool can quickly and reliably determine – by forming a checksum over larger
contiguous areas – whether there are differences. If there are no differences between the cal-
ibration RAM contents in the ECU and the file modified using the tool, this area does not need
to be transferred. If the memory area with the calibration parameters is not clearly defined, or
if it includes parameters that are modified by the ECU software, a checksum calculation always
shows a difference and the parameter values are transmitted, either from the ECU to the XCP
Master or in a reverse direction. Depending on the transmission speed and amount of data, this
transmission could take several minutes.
Another advantage of clearly defined memory segments is that the memory area for initial val-
ues in flash memory can be used for offline calibration. The contents of the flash memory are
defined using flashable hex files. If the calibration tool knows the location of parameters in the
hex file, it can modify their values and implement new initial values in the ECU by flashing the
modified hex file.
The calibration tool not only needs to know the location of parameters in RAM, but also the ini-
tial values in flash. A prerequisite is that the RAM memory segment must be initialized by copy-
ing from an identically laid out memory segment in flash, as is the usual practice in most com-
pilers/linkers. If the addresses of parameters in RAM are in the A2L file, it is only necessary to
let the tool know the offset to the start address of the calibration RAM, which it must add to get
to the start address of the relevant flash area. This offset then applies to each individual param-
eter in the A2L.
The calibration tool can then either generate flashable hex files for this area itself, or it can
place them directly on the original hex files of the linker to modify the initial values of param-
eters in the hex file.
78
3 Calibration Concepts
3.3 Flash Overlay
Many microcontrollers offer options for overlaying memory areas in flash with internal or exter-
nal RAM. This process is referred to as flash emulation or flash overlay. A lot is possible, from
the use of a Memory Management Unit all the way to dedicated mechanisms that precisely serve
this purpose. In this case the parameters are created as parameters in flash just as in calibra-
tion concept 1. This method offers enormous advantages compared to the described calibration
concept 2 “Parameters in RAM”:
> No distinction is made between flash and RAM addresses. The flash addresses are always
located in the A2L file, the hex file and linker-map file. This produces clear relationships, the
hex file is directly flashable and the A2L file matches it exactly.
> The overlay can be activated or deactivated as a whole, which enables lightning-quick swap-
ping between values in flash and those in RAM. They are referred to as the RAM page and the
flash page of a memory segment. XCP supports control of memory page swapping with special
commands.
> The memory pages might be swapped separately, e.g. for XCP access and ECU access, i.e. XCP
could access a memory page while the ECU software works with the other page. This permits
such operations as downloading of the offline calibration data to RAM, while the ECU is still
working with the flash data; this avoids potential inconsistencies that could be problematic
on a running ECU.
> The overlay with RAM does not need to be complete and it can be adapted to the application
case. It is possible to work with less RAM than with flash. More on this later.
A typical procedure for connecting the calibration tool to the ECU with the subsequent down-
load of values that were calibrated offline appears as follows:
Connects to the ECU
CONNECT
Connects XCP Master to RAM page
SET_CAL_PAGE XCP to RAM
Checksum calculation
CALC_CHECKSUM
When a difference has been detected in the checksum calculation over the RAM area, first the
user is normally asked how to proceed. Should the contents of ECU RAM be sent to the Master, or
should the contents of a file on the Master page be sent to the ECU’s RAM? If the user decides to
write the offline changes to the ECU, the subsequent process appears as follows:
ECU should use the dataset of the flash page
SET_CAL_PAGE ECU to FLASH
Copy file from Master to the RAM page
DOWNLOAD …
ECU should use the dataset of the RAM page
SET_CAL_PAGE ECU to RAM
Afterwards, the memory page is always switched over to RAM, so that parameters can be
modified. But the user can also explicitly indicate which memory page should be active in the
ECU. For example, the behavior of the RAM parameter set can be compared to that of the flash
parameter set, or in an emergency it can be switched back to a proven parameter set in flash at
lightning speed.
3.4 Dynamic Flash Overlay Allocation
79
3.4 Dynamic Flash Overlay Allocation
The concepts for calibration RAM described so far are unproblematic if sufficient RAM is avail-
able for all parameters. But what if the total number of parameters does not fit into the avail-
able RAM area?
Here, it is advisable to overlay flash with RAM dynamically and do not overlay the affected flash
memory with RAM until the actual write access to a parameter. This procedure can occur with a
certain granularity and – depending on the implementation – it may be transparent to the cal-
ibration tool from the XCP perspective. If the XCP driver detects a write access to flash in the
ECU which would lead to a change, a part of calibration RAM is used to copy over the relevant
part of flash and activate the overlay mechanism for this part. This involves allocating the RAM,
i.e. in a fixed layout and it is identified as utilized. However, the resources of the calibration
RAM are limited. During the calibration process, RAM area that has already been allocated is
no longer released, so the available calibration RAM dwindles with further requests. If the RAM
resources are used up and a new allocation is required, the user is informed of the exhausted
RAM resources. The user is offered the option of flashing or saving the changes made up to that
point. This frees up the allocated RAM area again and the user can once again calibrate. The
variant in which the ECU autonomously flashes the previously changed parameters is usually
ruled out here for the reasons already cited in calibration concept “Parameter in Flash”.
In some cases, the download of a parameter set created offline might not be executable due
to insufficient RAM resources. The only alternative is to flash it. The user can always cancel the
changes from the tool and this releases the allocated RAM blocks again.
In this concept, page swapping between the RAM and flash pages is also possible without any
limitations.
The parameters should be organized together in flash according to function, so that the avail-
able RAM blocks can be used as efficiently as possible. The software developer then specifies
that the parameters, which belong together thematically, also lie in a contiguous memory area.
After copying to RAM, the parameters needed for tuning the particular function are fully ready
for use.
80
3 Calibration Concepts
3.5 RAM Pointer Based Calibration Concept per AUTOSAR
This concept does not require the use of an AUTOSAR operating system; it can even be used in a
different environment – e.g. without an operating system. The concept exhibits a key similar-
ity to the previous concept. The primary difference is that the substitution of flash for RAM is
not implemented by hardware mechanisms, but by software mechanisms instead. The calibra-
tion parameters are always referenced by pointers from the ECU software. Flash or RAM con-
tents are accessed by changing this pointer. The flash parameters to be modified are copied to
a defined block with available RAM. This method can be implemented fully transparently from
the XCP perspective, just as in the previous method. As an alternative, the user of the calibra-
tion tool can explicitly select the parameters to be modified by preselecting the desired param-
eters. The advantage of this is that resource utilization and loading are visible to the user and
the user is not surprised by a lack of memory in the midst of working.
3.5.1 Single Pointer Concept
The pointer table is located in RAM. When booting the ECU, all pointers indicate the parame-
ter values in flash. The location and parameters of the calibration RAM are indeed known, but
it does not yet contain any parameter values after booting. Initially, the application works
entirely from flash.
FLASH
Pointertable
RAM
Figure 52:
Parameters
Initial situation
after booting
When the user selects a parameter from the A2L file for the first time after booting and wishes
to write access it, this triggers a copying operation within the ECU first. The XCP Slave deter-
mines that the address to which the access should be made is located in the flash area, and it
copies the parameter value to the calibration RAM. A change is also made in the pointer table
to ensure that the application no longer gets the parameter value from flash, but instead from
the RAM area:
3.5 RAM Pointer Based Calibration Concept per AUTOSAR
81
FLASH
Pointertable
RAM
Figure 53:
Parameters
Pointer change and
copying to RAM
The application continues to get the parameter value via the pointer table. But since the pointer
indicates the RAM address, the value is retrieved from there. As a result, the user can change
the parameter value via XCP and observe the effects of the change in the measurement. The dis-
advantage of this method is that an entry in a pointer table must be available for each parame-
ter and in turn the method is associated with substantial additional RAM memory requirements
for the pointer table.
The next figure illustrates the problem. Three parameters of a PID controller (P, I and D) are con-
tained in an ECU’s flash area. The RAM addresses and parameter values in RAM are also already
changed in the pointer table.
Parameter Flash
Pointertable
RAM
Addr.
Content
Addr.
Addr.
Content
P 0x0000100A 0x11
0x000A100A
0x000A100A 0x44
I
0x000012BC 0x22
0x000A100B
0x55
0x000A100B
D 0x00007234 0x33
0x000A100C
0x000A100C
0x66
Figure 54: Pointer table for individual parameters
Calibration concepts are very important, because RAM resources are scarce. Large RAM pointer
tables would make a concept self-defeating.
To avoid having to create a pointer for each individual parameter and having the method be
used as such, the parameters can be combined into structures. This requires just one pointer
per structure. When the user selects a parameter, not only is this parameter copied to RAM, but
so is the entire associated structure. The granularity of the structures is of key importance here.
With large structures only a few pointers are necessary. In turn, this means that with the deci-
sion for a specific parameter, a rather large associated structure is copied to the RAM area and
this can cause the limits of calibration RAM space to be reached quickly.
82
3 Calibration Concepts
Example:
The calibration RAM should be 400 bytes in size. Four structures are defined in the software with
the following parameters:
Structure A: 250 bytes
Structure B: 180 bytes
Structure C: 120 bytes
Structure D: 100 bytes
When the user selects a parameter from structure A, the 250 bytes are copied from flash to the
calibration RAM, and the user has XCP access to all parameters located in structure A. If the cali-
bration task is limited to the parameters of this structure, the calibration RAM is fully sufficient.
However, if the user selects another parameter located in a different structure, e.g. structure
C, these 120 bytes must also be copied to the calibration RAM. Since the calibration RAM can
handle 400 bytes, the user can access all parameters of structures A and C simultaneously.
If another selected parameter is not located in structure C, but rather in structure B, the 180
bytes of structure B would have to be copied to RAM in addition to the 250 bytes of structure A.
However, since the space in RAM is inadequate for this, the user indeed has access to the param-
eters of structure A, but not to the data of structure B, because the ECU cannot execute the copy
command.
You can learn more about how this approach works in CANape. Start CANape with the “AUTOSAR
Single Pointered Demo” project. You will find more information on its use in CANape on the
“Introduction” page of the project.
You will find a source code example under the “Demos” category at the Vector Download Center.
A code example on how to use the calibration concept is contained in the “XCP Sample Imple-
mentation” under <Installation DIR>\Samples\CAN\CAN MPC55xx\XCPDemo.
3.5.2 Double Pointer Concept
A disadvantage of the single pointer concept is that memory page swapping is not easy to imple-
ment. The calibration tool could simply describe the pointer table completely for page swap-
ping, but this is not feasible in a short period of time without resulting in temporary inconsis-
tencies and side effects. A tool-transparent implementation would double the memory space
requirement for the pointer table, because when swapping the memory page into flash, a copy
of the previous pointer table would have to be created with RAM pointers.
For applications with large pointer tables, a transparent implementation or a fully consistent
swapping, there is the option of extending the method to a double pointer concept. To explain
how this is done, we return once again to the initial RAM setting.
3.6 Flash Pointer Based Calibration Concept
83
Figure 55 represents the pointer table. It lies in RAM. As already mentioned, this table must be
copied from flash into RAM. As a result, this table lies in flash memory. If another pointer is now
used (a table pointer), which points to either the pointer table in RAM or in flash, one arrives
at a double pointer solution.
FLASH
RAM
Pointertable
FLASH
Pointertable
RAM
Figure 55:
Tablepointer
Double pointer concept
The parameter values are initially accessed via the table pointer. If the table pointer indicates
the pointer table in RAM, the application essentially accesses the actual parameters via the con-
tents of the RAM pointer table. The low access speed and the creation of more program code are
disadvantages of this solution.
3.6 Flash Pointer Based Calibration Concept
This method was patented several years ago by the company ZF Friedrichshafen under the name
“InCircuit2” and bears a strong resemblance to the pointer-based concept of AUTOSAR. Here
too, the application in the ECU accesses parameter data using a pointer table. However, this
pointer table is not located in RAM, but in flash instead. Changes to the pointer table can there-
fore only be made by flash programming. A tool-transparent implementation is not possible.
The advantage lies in the RAM memory that is saved since it no longer contains the pointer
table.
You can find out how this approach works in CANape. Start CANape with the “InCircuit2” project.
You will find more information on its use in CANape on the “Introduction” page of the project.
84
4 Application Areas of XCP
85
4 Application Areas of XCP
86
4 Application Areas of XCP
When ECU calibrators think about the use of XCP, they are usually fixated on use of the proto-
col in the ECU.
Simulink
Slave
Prototype or
ECU Hardware
Slave
XCP
Measurement/
Calibration
Master
Slave
PC
Hardware*
EXE/DLL
Slave
HIL/SIL Systems
Slave
Figure 56:
Application areas and
* Debug Interfaces, Memory Emulator, ...
application cases
In a survey of development processes, one encounters many different solution approaches for
the development of electronics and software. HIL (Hardware in the Loop), SIL (Software in the
Loop) and Rapid Prototyping are keywords here and they describe different scenarios. They
always have a “plant” and a “controller” in common.
Manipulated Disturbance
Offset
Variable
Variable
Reference Variable
Controlled Variable
Controller
Plant
(Set Value)
(Actual Value)
Figure 57: Plants and controllers
In the context of automotive development, the controller is represented by the ECU and the
plant is the physical system to be controlled such as the transmission, engine, side mirrors, etc.
The rough subdivision is made between different development approaches according to whether
the controller or the plant runs in real or simulated mode. Some combinations will be described
in greater detail.
4.1 MIL: Model in the Loop
87
4.1 MIL: Model in the Loop
Simulink
Controller Model
Plant Model
Figure 58:
Model in the Loop
in Simulink
In this development environment, both the controller and the plant are simulated as a model. In
the example shown, both models run in Simulink as the runtime environment. The capabilities
of the Simulink runtime environment are available to you for analyzing the behavior.
To realize the convenience of a measurement and calibration tool like CANape in an early devel-
opment phase, an XCP Slave can be integrated in the controller model. In an authoring step,
the Slave generates the A2L that matches the model and the user already has the full range of
convenient operating features with visualization of process flows in graphic windows, access to
characteristic curves and maps and much more.
Simulink
Controller Model
Plant Model
CANape
Figure 59:
CANape as
Simulink
measurement and
XCP Server
A2L
calibration tool with
Simulink models
Neither a code generation step nor instrumentation of the model is necessary for this. Time
stamps are also included with transmissions over XCP. CANape completely adapts to the time
behavior of the Simulink runtime environment here. Whether the model is running faster or
slower than in real time is of no consequence. For example, if the functional developer uses the
Simulink Debugger in the model to step through the model, CANape still takes the time trans-
mitted via XCP as the reference time.
88
4 Application Areas of XCP
4.2 SIL: Software in the Loop
Simulink
Controller Model
Plant Model
Code generation
Figure 60:
Controller Model
Software in the
Windows DLL
Loop with Simulink
environment
In this development step, code is generated from the model of the controller, which is then
used in a PC-based runtime environment. Naturally, the controller may also have been devel-
oped without any sort of model-based approach. The plant continues to be simulated. XCP can
be used to measure and calibrate the controller. If the controller originates from a Simulink
model, a code generation step (Simulink Coder with the target “CANape”) is used to generate
the C code for a DLL and the associated A2L. If the Controller development is conducted based
on manually written code, it is embedded in a C++ project that is delivered with CANape.
After compiling and linking, the DLL is used in the CANape context. With the support of the XCP
connection, the algorithms in the DLL can be measured and calibrated exactly as if the applica-
tion were already integrated in an ECU.
Simulink
Controller Model
Plant Model
Code generation
Controller Model
CANape
Windows DLL
A2L
Figure 61:
CANape as SIL
development platform
4.3 HIL: Hardware in the Loop
89
4.3 HIL: Hardware in the Loop
Many different kinds of HIL systems are available. They range from very simple, cost-effective
systems all the way to very large and expensive expansion stages. The following figure shows
the rough concept:
Controller Model
HIL Platform
I/O
Plant Model
Figure 62:
ECU
HIL solution
The controller algorithm runs in a microcontroller platform (e.g. the ECU), while the plant con-
tinues to be simulated. Depending on the parameters and the complexity of the plant and the
necessary I/O, requirements of the HIL platform and the associated costs can rise steeply. Since
the ECU runs in real time, the model of the plant must also be computed in real time.
To now introduce XCP for optimization appears trivial, because another ECU is being added. The
whole system looks like this:
Controller Model
A2L
HIL Platform
I/O
CANape
Figure 63:
Plant Model
HIL with CANape
as measurement
ECU
and calibration tool
From CANape, the user has access to the algorithms in the ECU over XCP.
90
4 Application Areas of XCP
The Vector Tool CANoe is also used by many customers as a HIL system. With CANoe, a HIL sys-
tem might look like this:
CANoe RT User PC
Ethernet
CANoe RT Server
CAN
LIN
Plant Model
MOST
A2L
FlexRay
Digital I/O
Analog I/O
XCP
CANape
Figure 64:
ECU
CANoe as HIL system
The ability to access XCP data directly from CANoe for testing purposes results in the following
variant as well:
CANoe RT User PC
A2L
Ethernet
CANoe RT Server
CAN
LIN
Plant Model
XCP
MOST
FlexRay
Digital I/O
Analog I/O
Figure 65:
CANoe as HIL
system with XCP
ECU
access to the ECU
Here the model of the plant runs on the CANoe real-time server. At the same time, XCP access
to the ECU is also realized from CANoe. This gives a tool simultaneous access to the plant and
the controller.
4.4 RCP: Rapid Control Prototyping
91
To round out the picture, yet another HIL solution option should be mentioned. The plant might
also run as a DLL in CANape. This gives the user full access to the plant and to the controller
over XCP.
ECU
CANape
Plant Model
A2L
Windows DLL
XCP
Plant
A2L
XCP
ECU
Figure 66: CANape as HIL solution
4.4 RCP: Rapid Control Prototyping
In this development phase, the control algorithm runs on real-time hardware instead of an ECU.
This situation often occurs when the necessary ECU hardware is not yet available. Several plat-
forms come in question as suitable hardware: from simple evaluation boards all the way to spe-
cial automotive-level hardware solutions, depending on which additional requirements need to
be fulfilled. Here too, integration with XCP helps in setting up an OEM-independent tool chain.
Controller Model
CANape
EVA Board
A2L
XCP
I/O
Plant
Figure 67: RCP solution
The concepts “Rapid” and “Prototyping” describe the task very well. The aim is to develop a
functional prototype as quickly as possible, to use and test it in the runtime environment. This
just requires simple work steps throughout the entire process.
92
4 Application Areas of XCP
In the literature, the RCP approach is frequently subdivided into two areas: fullpassing and
bypassing.
As depicted in Figure 67, the entire controller runs on separate real-time hardware. This method
is known as fullpassing, because the entire controller runs on the controller hardware. It must
have the necessary I/O to be able to interface with the plant. Very often, it is only possible to
fulfill technical requirements for the I/O with suitable power electronics.
It is not only the I/O that represents a challenge; often functional elements of the ECU software
(e.g. network management) are needed to enable functionality in a more complex network.
However, if a complete ECU is used for Rapid Control Prototyping instead of a general control-
ler platform, the complexity of the flash process, the size of the overall software, etc. all work
against the requirement for “Rapid” development.
In summary: the use of an entire ECU as the runtime environment for the controller offers the
advantage that the necessary hardware and software infrastructure for the plant exists. The dis-
advantage lies in the high degree of complexity.
The concept of bypassing was developed to exploit the advantages of the ECU infrastructure
without being burdened by the disadvantages of high complexity.
4.5 Bypassing
In Figure 68, the ECU is connected to the plant. The necessary I/O and software components are
available in the ECU. In the bypassing hardware, an algorithm A1 runs, which occurs in Version
A of the ECU. A1 is a new variant of the algorithm and should now be tried out on the real plant.
ECU
A2L
XCP
Bypassing Hardware
CANape
Bypassing
Hardware
A2L
XCP
I/O
Controller Model
ECU
Plant
Figure 68: Basic principle of bypassing
4.5 Bypassing
93
The bypassing hardware (a VN8900 device in the figure) and the ECU are interconnected over
XCP. One goal here is to get the data needed for algorithm A1 from the ECU by DAQ; another
goal is to stimulate the results of A1 back into the ECU. The following figure illustrates the sche-
matic flow:
Bypassing Hardware
Algorithm A1
2.
Bypassing
Coordinator
3.
1. XCP 4.
Algorithm A
ECU
Figure 69:
Bypassing flow
Depicted in the ECU is a blue function block in which the algorithm A runs. To ensure that A1 can
now be used, the data enters algorithm A as an input variable and it is measured from the ECU
by DAQ. In step 1, the bypassing coordinator accepts the data and in step 2 it passes the data to
algorithm A1. A1 is computed by the bypassing hardware and in step 3 the result is passed back
to the bypassing coordinator; in step 4, it is transmitted to the ECU by STIM. The data is written
to the “location” at which the next function block in the Slave expects its input variables. This
makes it possible to use the value computed by algorithm A1 and not from A in the ECU’s over-
all control process. This method permits using a combination of the rapid substitution of algo-
rithms on the bypassing hardware that incorporates the I/O and the ECU’s basic software.
94
4 Application Areas of XCP
Of course, the performance limits of an XCP-on-CAN driver also affect bypassing. If short bypass-
ing times are needed, access to the ECU by DAQ and STIM may also be performed via the con-
troller’s debugging or trace interfaces. The Vector VX1000 measurement and calibration hard-
ware converts the data into an XCP-on-Ethernet data stream from the controller interface. In
this process, up to one megabyte of data can be transported into the ECU.
XCP
Bypassing
Bypassing Hardware
CANape
Hardware
A2L
XCP
Measurement & Calibration
Hardware VX1000
Debugging and Trace Interface
I/O
Controller Model
ECU
Plant
Figure 70: Bypassing with real-time bypassing hardware and fast ECU access
4.6 Shortening Iteration Cycles with Virtual ECUs
95
4.6 Shortening Iteration Cycles with Virtual ECUs
Stimulation with data is necessary to optimize the algorithm in the ECU with the help of XCP.
This can be done in the ECU in the framework of test drives. But there is yet another solution
that is available with XCP, in which the algorithm does not run on an ECU; rather it runs on the
PC in the form of executable code or as a model in Simulink in the form of a “virtual ECU.” This
virtual ECU does not need to run in real time, because in this case no connection to a real system
exists. It can run significantly faster – depending on the PC’s computing power.
The algorithm is stimulated by a previously logged measurement file, which contains all signals
that are needed as input signals for the algorithm. The connection to CANape is set up over XCP.
The user can perform the parameterization and measurement configuration. Afterwards, exe-
cution is started. Here the data from the test drive is fed into the algorithm as stimulation and
the desired measurement parameters from the application are simultaneously measured out and
saved to a measurement file.
Para-
MDF
meter
test drive
Application
5. Analyze
1. Set parameters
2. Start
Simulink/
CANape
DLL
3. Send test drive data
4. Measurement data
Slave
Figure 71:
New
Short calibration
MDF
cycles with
virtual ECUs
96
4 Application Areas of XCP
After the calculation has been completed, a new measurement file is available to the user for
analysis of ECU behavior. The length of time of the new measurement file precisely matches the
length of the input measurement file. If the duration of a test drive is one hour, the algorithm
on the PC might calculate the entire test drive in just a few seconds. Then a measurement result
exists, which corresponds to a test of one hour duration. Based on the data analysis, the user
makes decisions about parameterization and the iteration cycle is repeated.
CANape
Application as EXE or DLL on PC
Parameterization
Set values in
via XCP
workspace
Start
Start
Send measurement
data
Calculate model
Receive new
Send measurement
measurement data
values from the model
Analyze the
End model calculation
new data
Figure 72:
New software version
Process flow
with virtual ECUs
To shorten the iteration cycles, the algorithm is always stimulated with the same data. That
makes the results with different parameters much more comparable, because the results are
only influenced by the parameters that differ.
This process can of course be automated. The integrated script language of CANape performs an
analysis of the measurement results, from which parameter calibration settings are derived and
automatically executed. It is also possible to have the process controlled by an external optimi-
zation tool such as MATLAB over the CANape automation interface.
4.6 Shortening Iteration Cycles with Virtual ECUs
97
98
5 Example of an XCP Implementation
99
5 Example of an XCP Implementation
100
5 Example of an XCP Implementation
To make it possible for an ECU to communicate over XCP, it is necessary to integrate an XCP driver
in the ECU’s application. The example described below is of the XCP driver which you can down-
load free of charge at the Download Center of the Vector website (www.vector.com/xcp-driver).
This packet also contains some sample implementations for various transport layers and tar-
get platforms. The driver consists of the protocol-Layer with the basic functionality needed for
measurement and calibration. It does not include features such as Cold Start Measurement,
Stimulation or flashing. You can purchase a full implementation as a product that is integrated
in the Vector CANbedded or AUTOSAR environment.
The XCP protocol layer is placed over the XCP transport layer, which in turn is based on the actual
bus communication. The implementation of the XCP protocol layer only consists of a single C
file and a few H files (xcpBasix.c, xcpBasic.h, xcp_def.h and xcp_cfg.h). The examples include
implementations for various transport layers, e.g. Ethernet and RS232. In the case of CAN, the
transport layer is normally very simple and the various XCP message types are mapped directly
to CAN messages. There are then separate fixed identifiers for the Tx and Rx directions.
The software interface between the transport and protocol layers is very simple. It contains just
a few functions:
> When the Slave receives an XCP message over the bus, it first arrives in the communication
driver, which routes the message to the XCP transport layer. The transport layer informs the
protocol layer about the message with the function call XcpCommand().
> If the XCP protocol layer wishes to send a message (e.g. a response to an XCP command from
the Master or a DAQ message), the message is routed to the transport layer by a call of the
ApplXcpSend() function.
> The transport layer informs the protocol layer that the message was successfully sent by the
function call XcpSendCallBack().
5 Example of an XCP Implementation
101
Application
r
t
t
XcpEvent
XcpIni
XcpBackground
ApplXcpGetPointe
XCP Protocol Layer
ion - XCP Transpor
k
at
Layer Interface
d
Applic
ommand
ApplXcpSen
XcpC
XcpSendCallbac
XCP Transport Layer
Physical Layer
Figure 73:
Incorporating
Bus
the XCP Slave
in the ECU code
The interface between the application and the protocol layer can only be implemented via four
functions:
> The application activates the XCP driver with the help of XcpInit(). This call is made once in
the starting process.
> With XcpEvent(), the application informs the XCP driver that a certain event has occurred
(e.g. “End of a computational cycle reached”).
> The call XcpBackground() lets the XCP driver execute certain activities in background (e.g.
calculation of a checksum).
> Since the addresses in A2L files are always defined as 40-bit values (32-bit address, 8-bit
address extension), the XCP driver uses the function ApplXcpGetPointer() to obtain a pointer
from a A2L-conformant address.
These interfaces are sufficient to integrate basic functionalities for measurement and calibra-
tion. Other interfaces are only needed for extended functions such as page swapping, identifi-
cation or seed & key. They are described in detail in documentation for the driver.
102
5 Example of an XCP Implementation
5.1 Description of Functions
void XcpInit (void)
Task:
Initialize the XCP driver
Description:
The application activates the XCP driver with XcpInit(). This command must be executed exactly
once before any sort of XCP driver function may be called.
void XcpEvent (BYTE event)
Task:
The application informs the XCP driver about which event occurred. A unique event number is
assigned to each event here.
Description:
In setting up the measurement configuration in the measurement and calibration tool, the user
selects which measured values should be synchronously acquired with which events. The infor-
mation on measured values and events originates from the A2L. The desired measurement con-
figuration is communicated to the XCP driver in the form of DAQ lists.
Example of an event definition in an engine controller:
XcpEvent (1);
// Event 1 stands for the 10-ms task
XcpEvent (2);
// Event 2 stands for the 100-ms task
XcpEvent (5);
// Event 5 stands for the 1-ms task
XcpEvent (8);
// Event 8 is used for ignition angle synchronous measurements
BYTE XcpBackground (void)
Task:
Execute background activities of the XCP driver.
Description:
This function should be called periodically in a background or idle task. It is used by the XCP
driver, for example, to compute the checksum, because the computation of a longer checksum
in XcpCommand() could take an unacceptably long time. With each call of XcpBackground(), a
partial checksum of 256 bytes is computed. The duration of a checksum computation therefore
depends on the call frequency of XcpBackground(). There are no other requirements for the call
frequency or periodicity. The return value 1 indicates that a checksum computation is currently
running.
5.1 Description of Functions
103
void XcpCommand (DWORD* pCommand)
Task:
Interpret an XCP command.
Description:
This function must be called each time the transport layer receives a XCP frame. The parameter
is a pointer to the frame.
void ApplXcpSend (BYTE len, BYTE *msg)
Task:
Transfer a frame to be sent to the transport layer.
Description:
With this call, the protocol layer sends a message to the transport layer for transmission to the
Master. The call XcpSendCallBack implements a handshake method between the protocol and
transport layers.
BYTE XcpSendCallBack (void)
Task:
The protocol layer uses this callback to inform the transport layer that the last message that was
transferred to ApplXcpSend() was successfully transmitted.
Description:
The protocol layer does not call an ApplXcpSend() command until XcpSendCallBack() indicates
that the prior message was successfully transmitted. XcpSendCallBack() returns the value 0
(FALSE) if the XCP driver is in idle. If there are more frames to be sent, ApplXcpSend() is called
directly from XcpSendCallBack().
BYTE *ApplXcpGetPointer (BYTE addr_ext, DWORD addr)
Task:
Convert an A2L-conformant address to a pointer.
Description:
The function maps the 40-bit A2L-conformant addressing (32-bit address + 8-bit address exten-
sion) that is sent by the XCP Master to a valid pointer. The address extension can be used, for
example, to distinguish different address areas or memory types.
104
5 Example of an XCP Implementation
5.2 Parameterization of the Driver
In many respects, the XCP driver is scalable and parameterizable to properly handle the wide
variety of functional content, transport protocols and target platforms. All settings are made in
the parameter file xcp_cfg.h. In the simplest case, they appear as follows:
/* Define protocol parameters */
#define kXcpMaxCTO 8 /* Maximum CTO Message Length */
#define kXcpMaxDTO 8 /* Maximum DTO Message Length */
#define C_CPUTYPE_BIGENDIAN /* byte order Motorola */
/* Enable memory checksum */
#define XCP_ENABLE_CHECKSUM
#define kXcpChecksumMethod XCP_CHECKSUM_TYPE_ADD14
/* Enable calibration */
#define XCP_ENABLE_CALIBRATION
#define XCP_ENABLE_SHORT_UPLOAD
/* Enable data acquisition */
#define XCP_ENABLE_DAQ
#define kXcpDaqMemSize (512) /* Memory space reserved for DAQ */
#define XCP_ENABLE_SEND_QUEUE
For a CAN transport layer, the appropriate CTO and DTO parameters of eight bytes are set. The
driver must know whether it is running on a platform with Motorola or Intel byte order, in this
case a Motorola-CPU (Big Endian). The remaining parameters activate the functionalities: mea-
surement, calibration and checksum computation. The algorithm for checksum computation is
configured (here summing of all bytes into a DWORD) and the parameter of the available mem-
ory is indicated for the measurement (here 512 bytes). The memory is primarily needed to store
the DAQ lists and to buffer the data during the measurement. The parameter therefore deter-
mines the maximum possible number of measurement signals. In the driver documentation you
will find more detailed information on estimating the necessary parameters.
5.2 Parameterization of the Driver
105
106
The Authors
The Authors
Andreas Patzer
Mr. Patzer graduated in Electrical Engineering from the Technical University of
Karlsruhe. In his studies he specialized in measurement and control engineering
and information and industrial engineering. In 2003, he joined Vector Informatik
GmbH in Stuttgart. Andreas Patzer has supported XCP projects from the very start,
since XCP was standardized by ASAM e.V. in the same year he was hired.
He currently manages the Customer Relations and Services area as a team leader
for the Measurement & Calibration product line.
The Authors
107
Rainer Zaiser
Mr. Zaiser has a degree in Electrical Engineering from the University of Stuttgart.
After graduating, he came directly to Vector Informatik GmbH in autumn 1988,
where he has helped to create many of the standards that have become established
in the automotive industry such as DBC, MDF, CCP, A2L and to a large extent XCP.
From the start, he headed up the Measurement & Calibration and Network
Interfaces product lines.
108
Table of Abbreviations and Acronyms
Table of Abbreviations and Acronyms
A2L
File extension for an ASAM 2MC language file
AML
ASAM 2 Meta Language
ASAM
Association for Standardisation of Automation and Measuring Systems
BYP
Bypassing
CAL
Calibration
CAN
Controller Area Network
CCP
CAN Calibration Protocol
CMD
Command
CS
Checksum
CTO
Command Transfer Object
CTR
Counter
DAQ
Data Acquisition, Data Acquisition Packet
DTO
Data Transfer Object
ECU
Electronic Control Unit
ERR
Error Packet
EV
Event Packet
FIBEX
Field Bus Exchange Format
LEN
Length
MCD
Measurement Calibration and Diagnostics
MTA
Memory Transfer Address
ODT
Object Descriptor Table
PAG
Paging
PGM
Programming
PID
Packet Identifier
RES
Command Response Packet
SERV
Service Request Packet
SPI
Serial Peripheral Interface
STD
Standard
STIM
Data Stimulation Packet
TCP/IP
Transfer Control Protocol / Internet Protocol
TS
Time Stamp
UDP/IP
Unified Data Protocol / Internet Protocol
USB
Universal Serial Bus
XCP
Universal Measurement and Calibration Protocol
Download
Sending of data from Master to Slave
Upload
Sending of data from Slave to Master
Literature & Web Addresses
109
Literature
XCP is specified by ASAM (Association for Standardisation of Automation and Measuring Systems).
You will find details on the protocol and on ASAM at: www.asam.net
Web Addresses
Standardization committees:
> ASAM, XCP protocol-specific documents, A2L specification, www.asam.net
Supplier of development software:
> MathWorks, information on MATLAB, Simulink and Simulink Coder, www.mathworks.com
> Vector Informatik GmbH, demo version of CANape, free of charge and openly available XCP
driver (basic version), comprehensive information on the topics of ECU calibration, testing
and simulation, www.vector.com
110
Table of Figures
Table of Figures
Figure 1: Fundamental communication with a runtime environment
8
Figure 2: The Interface Model of ASAM
9
Figure 3: An XCP Master can simultaneously communicate with multiple Slaves
10
Figure 4: Subdivision of the XCP protocol into protocol layer and transport layer
14
Figure 5: XCP Slaves can be used in many different runtime environments
15
Figure 6: XCP packet
19
Figure 7: Overview of XCP Packet Identifier (PID)
19
Figure 8: XCP communication model with CTO/DTO
20
Figure 9: Message identification
21
Figure 10: Time stamp
21
Figure 11: Data field in the XCP packet
22
Figure 12: The three modes of the XCP protocol: Standard, Block and Interleaved mode
24
Figure 13: Overview of the CTO packet structure
25
Figure 14: Trace example from a calibration process
30
Figure 15: Transfer of a parameter set file to an ECU’s RAM
31
Figure 16: Hex window
32
Figure 17: Address information of the parameter “Triangle” from the A2L file
33
Figure 18: Polling communication in the CANape Trace window
34
Figure 19: Events in the ECU
35
Figure 20: Event definition in an A2L
35
Figure 21: Allocation of “Triangle” to possible events in the A2L
36
Figure 22: Selecting events (measurement mode) for each measurement parameter
36
Figure 23: Excerpt from the CANape Trace window of a DAQ measurement
37
Figure 24: ODT: Allocation of RAM addresses to DAQ DTO
38
Figure 25: DAQ list with three ODTs
39
Figure 26: Static DAQ lists
39
Figure 27: Dynamic DAQ lists
40
Figure 28: Event for DAQ and STIM
41
Figure 29: Structure of the XCP packet for DTO transmissions
42
Figure 30: Identification field with absolute ODT numbers
43
Figure 31: ID field with relative ODT and absolute DAQ numbers (one byte)
43
Figure 32: ID field with relative ODT and absolute DAQ numbers (two bytes)
43
Figure 33: ID field with relative ODT and absolute DAQ numbers as well as fill byte
(total of four bytes)
44
Figure 34: Definition of which bus nodes send which messages
45
Figure 35: Representation of a CAN network
46
Figure 36: Example of XCP-on-CAN communication
47
Figure 37: Representation of an XCP-on-CAN message
47
Figure 38: Illustration of a CAN FD frame
48
Figure 39: Nodes K and L are redundantly interconnected
50
Figure 40: Communication by slot definition
50
Figure 41: Representation of a FlexRay communication matrix
51
Figure 42: Representation of the FlexRay LPDUs
52
Figure 43: Allocation of XCP communication to LPDUs
53
Figure 44: XCP packet with TCP/IP or UDP/IP
54
Table of Figures
111
Figure 45: XCP-on-SxI packet
55
Figure 46: Memory representation
56
Figure 47: Representation of driver settings for the flash area
58
Figure 48: Representation of the block transfer mode
61
Figure 49: Parameters in a calibration window
66
Figure 50: Signal response over time
66
Figure 51: Initial parameter setting in RAM
76
Figure 52: Initial situation after booting
80
Figure 53: Pointer change and copying to RAM
81
Figure 54: Pointer table for individual parameters
81
Figure 55: Double pointer concept
83
Figure 56: Application areas and application cases
86
Figure 57: Plants and controllers
86
Figure 58: Model in the Loop in Simulink
87
Figure 59: CANape as measurement and calibration tool with Simulink models
87
Figure 60: Software in the Loop with Simulink environment
88
Figure 61: CANape as SIL development platform
88
Figure 62: HIL solution
89
Figure 63: HIL with CANape as measurement and calibration tool
89
Figure 64: CANoe as HIL system
90
Figure 65: CANoe as HIL system with XCP access to the ECU
90
Figure 66: CANape as HIL solution
91
Figure 67: RCP solution
91
Figure 68: Basic principle of bypassing
92
Figure 69: Bypassing flow
93
Figure 70: Bypassing with real-time bypassing hardware and fast ECU access
94
Figure 71: Short calibration cycles with virtual ECUs
95
Figure 72: Process flow with virtual ECUs
96
Figure 73: Incorporating the XCP Slave in the ECU code
101
112
Appendix – XCP Solutions at Vector
Appendix – XCP Solutions at Vector
Vector made a significant effort in giving shape to the XCP standard. Its extensive know-how
and vast experience were utilized to provide comprehensive XCP support:
Tools
> The primary use area of CANape is in optimal parameterization (calibration) of electronic
control units (ECUs). During the system’s runtime, you calibrate parameter values and simul-
taneously acquire measured signals. The physical interface between CANape and the ECU is
over XCP (for all standardized transport protocols) or CCP.
> Complete tool chain for generating and managing the necessary A2L description files (ASAP2
Tool-Set and CANape with the ASAP2 Editor that is also available as a stand-alone tool).
> You use CANoe.XCP to access internal ECU values for testing and analysis tasks.
ECU interfaces
The VX1000 measurement and calibration hardware offers the option of equipping ECUs with
an XCP-on-Ethernet interface. This involves connecting a Plug on Device (POD) to the ECU for
direct access to the controller, e.g. over DAP, JTAG, Nexus, etc. The POD transmits the data to a
base module, which operates as an XCP Slave and provides the data to the XCP Master on the PC
over XCP on Ethernet. This makes it unnecessary to have an XCP Slave in the ECU. The user ben-
efits from a high measurement data throughput rate of up to 30 Mbyte/sec and short measure-
ment intervals of less than 15 µs.
Embedded Software
Communication modules with separate transport layers for CAN, FlexRay and Ethernet:
> XCP Basic – free download at www.vector.com/xcp-driver, only contains basic XCP functions.
Configuration of the XCP protocol and modification of the transport layer are performed man-
ually in the source code. You need to integrate XCP Basic in your project yourself.
> XCP Professional – contains useful extensions to the ASAM specification and enables tool-
based configuration. Available for Vector CANbedded basic software.
> MICROSAR XCP – contains the functional features of XCP Professional and is based on AUTO-
SAR specifications. Available for Vector MICROSAR basic software.
Services
> Consultation for using XCP in your projects
> Integration of XCP in your ECU
Training
> You can learn about the underlying mechanisms and models of the protocol in the “XCP Funda-
mentals Seminar”.
> In the “CANape with XCP on FlexRay Workshop” you learn about FlexRay fundamentals
and the special aspects of XCP on FlexRay are explained, in particular dynamic bandwidth
management.
Appendix – XCP Solutions at Vector
113
Special XCP support by CANape
CANape was the first MCD tool to support the XCP 1.0 specification and was also the first XCP on
FlexRay Master on the market.
A special technical feature of XCP on FlexRay is dynamic bandwidth management. Here, CANape
identifies the available bandwidth provided for XCP in the FlexRay ClusterP and it allocates
this bandwidth to the momentary application data traffic dynamically and very efficiently. The
available bandwidth is thereby optimally used for XCP communication.
Moreover, CANape has a DLL interface. It enables support of XCP on any desired (user-defined)
transport layer. This lets you integrate any desired test instrumentation or proprietary pro-
tocols in CANape. A code generator supports you in creating the XCP-specific share of such a
driver.
114
Index
Index
A
F
A2L
9, 10, 25, 33, 35, 39, 40, 41, 52, FIBEX
51, 52, 53
53, 57, 58, 63, 65, 66, 67, 68, 69, Flash memory
16, 17, 56, 57, 58, 59, 62
70, 88, 102, 103, 108
FLX_CHANNEL
52
Address extension
29, 33, 38, 101, 103
FLX_LPDU_ID
52
AML
25, 68, 108
FLX_SLOT_ID
52
ASAM
7, 8, 9, 55, 108
Fullpassing
92
ASAP2 Tool-Set
70
G
B
GET_CAL_PAGE
25, 57
Bandwith optimization
34
GET_DAQ_PROCESSOR_INFO
44, 60, 71
Bus load
34
BYP
108
H
Bypassing
44, 92, 93, 94
HIL
86, 89, 90, 91
C
L
CAN
7, 8, 14, 24, 29, 33, 38, 45, 46, 47, Linking
74, 88
51, 69, 94, 108
LPDU
52
CAN FD
48
CANape
95
M
CANoe
95
MIL
87
CANoe.XCP
95
MTA
30, 108
CCP
7, 8, 39, 45, 108
CMD
20, 25, 52, 108
O
Compiling
95
ODT
37, 38, 39, 40, 42, 43, 44, 60,
CTO
20, 21, 22, 25, 108
71, 108
CTR
54, 55, 108
OFFSET
52
CYCLE_REPETITION
52
P
D
PAG
108
DAQ
22, 32, 33, 34, 35, 36, 37, 38, Page
95
39, 40, 41, 42, 43, 44, 60, 62, 71, PGM
108
93, 94, 100, 102, 108
PID
8, 19, 21, 25, 42, 108
DBC
45
Polling
33, 34, 36
DOWNLOAD
30, 31, 61
DTO
20, 21, 22, 33, 37, 38, 42, 108
R
RAM
16, 17, 18, 30, 31, 37, 38, 39,
E
58, 62, 74, 76, 79, 80, 82
ECU
9, 68, 90, 92, 93, 108
Reboot
32
EEPROM
16, 31, 62
RES
20, 21, 28, 52, 108
ERR
20, 25, 28, 108
EV
29, 108
Event
35, 39, 41, 60, 62, 71, 102
Index
115
S
Segment
57, 58
SEGMENT_NUMBER
57
SERV
29, 108
SET_CAL_PAGE
25, 57
SHORT_UPLOAD
30, 33, 61
SIL
86, 88
STIM
33, 41, 42, 44, 60, 71, 93,
94, 95, 108
Stimulation
29, 63, 95
T
Task
102
TCP/IP
53, 54, 108
U
UDP/IP
53, 54, 108
USB
55, 108
V
VN8900
95
VX
94
VX1000
95
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V 2.0 4/20
Document Outline
- Table of Contents
- Introduction
- 1 Fundamentals of the XCP Protocol
- 2 ECU Description File A2L
- 3 Calibration Concepts
- 4 Application Areas of XCP
- 5 Example of an XCP Implementation
- The Authors
- Table of Abbreviations and Acronyms
- Literature
- Web Addresses
- Table of Figures
- Appendix – XCP Solutions at Vector
- Index