NXP Semiconductors MPC5644A, Reference Manual, Page: 1578 / 1735

FlexRay Communication Controller (FlexRay)
MPC5644A Microcontroller Reference Manual, Rev. 6
1578 Freescale Semiconductor
Additionally, the slot status field of the commit side is update after the update of the slot status field of the
transmit side, even if the commit side is locked by the application. This is implemented to provide the slot
status of the most recent transmission slot.
33.6.7 Individual message buffer search
This section provides a detailed description of the message buffer search algorithm.
The message buffer search determines for each enabled channel if a slot s in a communication cycle c is
assigned for frame or null frame transmission or if it is subscribed for frame reception on that channel.
The message buffer search is a sequential algorithm which is invoked at the following protocol related
events:
1. NIT start
2. slot start in the static segment
3. minislot start in the dynamic segment
The message buffer search within the NIT searches for message buffers assigned or subscribed to slot 1.
The message buffer search within slot
n searches for message buffers assigned or subscribed to slot n+1 .
In general, the message buffer search for the next slot n considers only message buffers which are
1. enabled, that is, FR_MBCCSRn[EDS] = 1, and
2. matches the next slot n , that is, FR_MBFIDRn[FID] = n , and
3. are the transmit side buffer in case of a double transmit message buffer.
On top of that, for the static segment only those message buffers are considered, that match the condition
of at least one row of
Table 33-122 . For the dynamic segment only those message buffers are considered,
that match the condition of at least one row of Table 33-123 . These message buffers are called matching
message buffers.
For each enabled channel the message buffer search may identify multiple matching message buffers.
Among all matching message buffers the message buffers with highest priority according to Table 33-122
for the static segment and according to Table 33-123 for the dynamic segment are selected.
Table 33-122. Message buffer search priority (static segment)
Priority MTD LCKS CMT CCFM
1
1
Cycle Counter Filter Match, see Section 33.6.7.1, Message buffer cycle counter filtering”
Description Transition
(highest) 0 1 0 1 1 Transmit buffer, matches cycle count, not locked
and committed MA
1
1 — 0 1 Transmit buffer, matches cycle count, not
committed SA
1 1 — 1 Transmit buffer, matches cycle count, locked SA
2 1 — — — Transmit buffer SA
3 0 0 n/a 1 Receive buffer, matches cycle count, not locked SB
(lowest) 4 0 1 n/a 1 Receive buffer, matches cycle count, locked SB