Image Processing Reference
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is required. Additionally, the safety requirement introduces the need to protect individual commu-
nication partners from faults of other partners by means of so-called guardians. Otherwise, errors of
one partner could cross-influence other partners thus violating safety demands.
Specific automotive issues complete the broad range of requirements forming the framework for
andofFlexRay.heseissuesrangefromtheuseofautomotivecomponentslikeX-tals,automotive
electro-magnetic compatibility (EMC) requirements, support for power management to conserve
battery power, support for electrical and optical physical layers, to a high bandwidth demand of at
least two times Mbps.
16.3 What is FlexRay?
Before the development of FlexRay was started, a comprehensive evaluation of the existing technolo-
gies took place. he results showed that none of the existing communication technologies could fulfill
the requirements to a satisfactory degree. hus the development of a new technology was started. he
resulting communication protocol FlexRay is an open, scalable, deterministic, and high-performance
communication technology for automotive applications.
A FlexRay network consists of a set of electronic control units (ECUs) with integrated communi-
cation controllers (CCs) (Figure .). Each CC connects the ECU to one or more communication
channels via a communication port, which in turn links to a bus driver (BD). The BD connects to
the physical layer of the communication channel and can contain a guardian unit that monitors the
TDMA access of the controller (the architecture of an ECU is depicted in Figure .). A communi-
cation channel can be as simple as a single bus wire but also be as complex as active or passive star
configurations.
FlexRay supports the operation of a CC with single or redundant communication channels. In
case of single communication channel configuration, all controllers are attached to the communi-
cation channel via one port. In case of redundant configuration, controllers can be attached to the
communication channels via one or two ports. Controllers that are connected to two channels can be
coniguredtotransmitdataredundantlyontwochannelsatthesametime.hisredundanttransmis-
sion allows the masking of a temporary fault of one communication channel and thus constitutes a
powerful fault-tolerance feature of the protocol. A second fault-tolerance feature related to transient
faults can be constructed by the redundant transmission of data over the same channels with a par-
ticular time delay between the redundant transmissions. his delayed transmission allows tolerating
transient faults on both channels under particular preconditions.
If the fault-tolerance property of two independent channels is not required for a specific applica-
tion, the channels can be used to transfer different data, thus effectively doubling the transmission
bandwidth.
Node A
Node B
Node C
Node D
Node E
Node F
Channel 0
Channel 1
FIGURE .
FlexRay network.
