Image Processing Reference
In-Depth Information
1.2 Automotive Networked Embedded Systems
Trends for networking also emerged in the automotive electronic systems where the ECUs are
networked by means of one of automotive-specific communication protocols for the purpose of
controlling one of the vehicle functions; for instance, electronic engine control, antilocking break
system, active suspension, telematics, and to mention a few. In Ref. [], a number of functional
domains have been identified for the deployment of automotive networked embedded systems. hey
include the power train domain, involving, in general, control of engine and transmission; the chassis
domain involving control of suspension, steering, and braking, etc.; the body domain involving con-
trol of wipers, lights, doors, windows, seats, mirrors, etc.; the telematics domain involving mostly the
integration of wireless communications, vehicle monitoring systems, and vehicle location systems;
and the multimedia and human-machine interface domains. he different domains impose varying
constraints on the networked embedded systems in terms of performance, safety requirements, or
Quality of Services (QoS). For instance, the power train and chassis domains will mandate real-time
control; typically bounded delay is required, as well as fault-tolerant services.
There are a number of reasons for the interest of the automotive industry in adopting mechatronic
solutions, known by their generic name as X-by-Wire, aiming to replace mechanical, hydraulic, and
pneumatic systems by electrical/electronic systems. he main factors seem to be economic in nature,
improved reliability of components, and increased functionality to be achieved with a combination
of embedded hardware and software. Steer-by-Wire, Brake-by-Wire, or hrottle-by-Wire systems are
representative examples of those systems. But, it seems that certain safety-critical systems such as
Steer-by-Wire and Brake-by-Wire will be complemented with traditional mechanical/hydraulic back-
ups, for safety reasons. he dependability of X-by-Wire systems is one of the main requirements, as
well as constraints on the adoption of this kind of systems. In this context, a safety-critical X-by-Wire
system has to ensure that a system failure does not lead to a state in which human life, property, or
environment is endangered; and a single failure of one component does not lead to a failure of the
whole X-by-Wire system []. When using Safety Integrity Level scale, it is required for X-by-Wire sys-
tems that the probability of a failure of a safety-critical system does not exceed the figure of
−
per
hour/system. his figure corresponds to the SIL level. Another equally important requirement for
the X-by-Wire systems is to observe hard real-time constraints imposed by the system dynamics; the
end-to-end response times must be bounded for safety-critical systems. A violation of this require-
ment may lead to performance degradation of the control system, and other consequences as a result.
Not all automotive electronic systems are safety critical. For instance, system(s) to control seats, door
locks, internal lights, etc. are not. Different performance, safety, and QoS requirements dictated by
various in-car application domains necessitate adoption of different solutions, which, in turn, gave
rise to a significant number of communication protocols for automotive applications. Time-triggered
protocols (TTP) based on TDMA medium access control technology are particularly well suited
for the safety-critical solutions, as they provide deterministic access to the medium. In this cate-
gory, there are two protocols, which, in principle, meet the requirements of X-by-Wire applications,
namely, TTP/C [] and FlexRay [] (FlexRay can support a combination of both time-triggered and
event-triggered transmissions). he following discussion will focus mostly on TTP/C and FlexRay.
The TTP/C is a fault-tolerant TTP; one of two protocols in the time-triggered architecture (TTA)
[]. The other one is a low-cost fieldbus protocol TTP/A []. In TTA, the nodes are connected by
two replicated communication channels forming a cluster. In TTA, a network may have two different
interconnection topologies, namely, bus and star. In the bus configuration, each node is connected to
two replicated passive buses via bus guardians. he bus guardians are independent units preventing
associated nodes from transmitting outside predetermined time slots, by blocking the transmission
path; a good example may be a case of a controller with a faulty clock oscillator, which attempts
to transmit continuously. In the star topology, the guardians are integrated into two replicated cen-
tralstarcouplers.heguardiansarerequiredtobeequippedwiththeirownclocks,distributedclock
