Module Operation
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SPNU563A–March 2018
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FlexRay Module
26.2.6.7.2 Startup Timeouts
The communication controller supplies two different μT timers supporting two timeout values, startup
timeout and startup noise timeout. The two timers are started when the communication controller enters
the COLDSTART_LISTEN state. The expiration of either of these timers causes the node to leave the
initial sensing phase (COLDSTART_LISTEN state) with the intention of starting up communication.
NOTE: The startup and startup noise timers are identical with the wakeup and wakeup noise timers
and use the same configuration values SUCC2.LT(20-0) and SUCC2.LTN(3-0) from the SUC
configuration register 2.
26.2.6.7.2.1 Startup Timeout
The startup timeout limits the listen time used by a node to determine if there is already communication
between other nodes or at least one coldstart node actively requesting the integration of others. The
startup timer is configured by programming SUCC2.LT(20-0) in the SUC configuration register 2.
The startup timeout time can be calculated from the contents of SUCC2.LT(20-0) (Refer to the FlexRay
Protocol Specification: pdListenTimeout)
The startup timer is restarted upon:
• Entering the COLDSTART_LISTEN state
• Both channels reaching idle state while in COLDSTART_LISTEN state
The startup timer is stopped:
• If communication channel activity is detected on one of the configured channels while the node is in
the COLDSTART_LISTEN state
• When the COLDSTART_LISTEN state is left
Once the startup timeout expires, neither an overflow nor a cyclic restart of the timer is performed. The
timer status is kept for further processing by the startup state machine.
26.2.6.7.2.2 Startup Noise Timeout
At the same time the startup timer is started for the first time (transition from STARTUP_PREPARE state
to COLDSTART_LISTEN state), the startup noise timer is started. This additional timeout is used to
improve reliability of the startup procedure in the presence of noise. The startup noise timer is configured
by programming SUCC2.LTN(3-0) in the SUC configuration register 2.
The startup noise timeout time can be calculated as the product of SUCC2.LT(20-0) * SUCC2.LTN(3-0)
(Refer to the FlexRay Protocol Specification: pdListenTimeout • gListenNoise)
The startup noise timer is restarted upon:
• Entering the COLDSTART_LISTEN state
• Reception of correctly decoded headers or CAS symbols while the node is in COLDSTART_LISTEN
state
The startup noise timer is stopped when the COLDSTART_LISTEN state is left.
Once the startup noise timeout expires, neither an overflow nor a cyclic restart of the timer is performed.
The status is kept for further processing by the startup state machine. Since the startup noise timer won’t
be restarted when random channel activity is sensed, this timeout defines the fall-back solution that
guarantees that a node will try to start up the communication cluster even in the presence of noise.
26.2.6.7.3 Path of Leading Coldstart Node (Initiating Coldstart)
When a coldstart node enters COLDSTART_LISTEN, it listens to its attached channels.
If no communication is detected, the node enters the COLDSTART_COLLISION_RESOLUTION state and
commences a coldstart attempt. The initial transmission of a CAS symbol is succeeded by the first regular
cycle. This cycle has the number 0.
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