Civil Engineering Reference
In-Depth Information
Fig. 5.4
Message cycle matrix
This initiative should result in a lighter, safer, more fuel-efficient and less expen-
sive X-by-wire vehicle which exhibits additional functionality. In such vehicles,
there are fewer environmentally unfriendly fluids to contend with, and the systems
are self-diagnosing, reconfigurable and easily adapted across vehicle platforms. X-
by-wire systems allow the tightest possible integration of distributed functionality
within the vehicle, in contrast to the discrete, often disjoint, operation of conven-
tional mechanical systems. The introduction of an X-by-wire vehicle infrastruc-
ture facilitates the implementation of many active safety improvements, based on
advanced electronic systems; examples include autonomous cruise control, colli-
sion avoidance, automated parking assist and autonomous driving. The European
SPARC Project is an example of an X-by-wire accident-avoiding vehicle with a
Safety Decision Control System (SDCS). A necessary prerequisite to such highly
integrated X-by-wire systems is a fault-tolerant communication infrastructure. The
following section describes a prototype experimental brake-by-wire and steer-by-
wire system based on TTCAN.
5.2.2
TTCAN Network Implementation
At the time this X-by-wire prototype was developed, there were no TTCAN proto-
col engines available in silicon. As a result, a system based on the Infineon C515C
microcontroller and an application layer based on the TTCAN protocol with level
1 synchronization was implemented in software. Figure
5.4
illustrates the TTCAN
message matrix used. The cycle matrix consists of two basic cycles. Each basic
cycle commences with a reference message, which is followed by either a steer-
ing wheel position message or a brake pedal angle message, and terminates with
a feedback message. The reference message is used to synchronise the network by
resetting the cycle time in each network node. The reference message also contains
the current basic cycle count, which is used to help to ensure that all nodes observe
the correct schedule pattern. The TTCAN local clock is implemented using the mi-
crocontroller's on-chip timers and the TTCAN triggers are implemented using real-
time interrupts generated by the overflow of these timers.
