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12lA UTOMOTIVE 2008l SPECIAL EDITION FLEXRAY
transferred to MATLAB/Simulink, where the data is used
as parameters for FlexRay communication blocks from the
RTI FlexRay Configuration Blockset. Application-specific
Simulink models can be created using the RTI FlexRay Configuration
Blockset as a basis, with data provided by the
configuration tool. The block attributes are filled with data
generated by the dSPACE FlexRay Configuration Tool. The
blockset contains additional blocks that can be used for
task execution control, interrupt and error handling, status
information, and controller reset. The hardware is connected
via the FlexRay interface to the FlexRay bus, and from
there to the FlexRay ECUs which are the units under test.
The FlexRay Configuration Package is not
only concerned with simple restbus
simulation for mimicking the network
behavior, but also allows target-oriented
failure simulation by checking potential
failure cases. For example, the package
can be used to insert logical corruptions
in FlexRay communication to allow a
cyclic FlexRay frame to be switched in or
out, CRC algorithms to be switched
during run time, etc.
In addition, it is also possible to have a failure
insertion on the physical level by
simulating broken wires, short circuits,
etc., or to vary the termination resistance.
This can be done with suitable failure
insertion hardware for differential
busses.
The dSPACE FlexRay Configuration Tool
can create several kinds of time-triggered
tasks for the various scenarios. In addition
to these test functions for FlexRay
networks, the tool can also be used in
connection with the RTI Bypass Blockset
and the Universal Measurement and
Calibration Protocol (XCP). XCP is the successor to the
much-used CAN Calibration Protocol (CCP). The advantage
of XCP is that it provides strict separation between the protocol
and the transport level, and is therefore open for the
implementation of FlexRay or even future bus systems.
XCP on FlexRay is part of the XCP family standardized by
ASAM. The XCP concept is based on the master/slave principle,
with the electronic control unit (ECU) as the slave.
XCP on FlexRay is already being used in numerous projects,
especially where the CAN bus has been replaced by
FlexRay.
Task-Synchronous Bypassing via XCP
on FlexRay
Due to the complexity of modern electronic control units
(ECUs) and the limited time available for the development
of new ECU generations, the entire ECU software is developed
from scratch in only very few cases. Instead the existing
ECU code is adapted or extended. The external
bypass method is an efficient approach in this context, allowing
new algorithms to be developed on a rapid prototyping
system while the original ECU executes all the functions
that remain unchanged. The input and output variables
of the bypass model are exchanged, and task execution
on the ECU and the prototyping system is synchronized
via existing ECU interfaces such as XCP on FlexRay.
The external bypass approach gives the greatest flexibility
possible during the design phase, since there are almost
no resource constraints such as RAM, ROM, processor
performance, or I/O channels. Real-time behavior is guaranteed
even for complex bypass functions. In addition, the
autoboot options of the prototyping systems allow the
behavior of new functions to be validated in realistic scenarios,
for example during test drives.
Fig. 1: Workflow with dSPACE’s FlexRay solution.
© automotive
In this configuration example, the dSPACE MicroAutoBox
is used as a real-time prototyping system. The bypass function
is calculated synchronously to an ECU task. As soon
as all the input data of the bypass model is available, an
interrupt is triggered and the bypass task on the MicroAutoBox
is executed. Alternatively, task execution on the two
systems can be synchronized by means of the FlexRay
message schedule. Execution of the bypass task is then
purely time-driven (Fig. 2).
Real-Time ECU Access via XCP on Flex-
Ray
For developing ECU functions by means of the external
bypass approach, it is usually necessary to configure the
bypass interface in the modeling environment and to change
the input and output signals of the bypass model
without ECU code modifications. The RTI Bypass Blockset
provides a generic user interface for this purpose, with the
same look and feel no matter what ECU interface is actually
used for bypassing.
The XCP on FlexRay option of the RTI Bypass Blockset is
based on the dSPACE FlexRay Configuration Package. The