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Chapter 13 FlexRay Communication Controller (FLEXRAY)
MC9S12XF - Family Reference Manual, Rev.1.19
582
Freescale Semiconductor
13.6.7
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, i.e. MBCCSRn.EDS = 1, and
2. matches the next slot n, i.e. 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 13-110. For the dynamic segment only those message buffers are considered,
that match the condition of at least one row of Table 13-111. 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 13-110for the static segment and according to
Table 13-111 for the dynamic segment are selected.
Table 13-110. Message Buffer Search Priority (static segment)
Priority
MTD
LCKS
CMT
CCFM
(1)
Description
Transition
(highest) 0
1011
transmit buffer, matches cycle count, not locked and committed
MA
1
-
0
1
transmit buffer, matches cycle count, not committed
SA
1
-
1
transmit buffer, matches cycle count, locked
SA
2
1
-
transmit buffer
SA
3
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