FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 26-123
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. enable (MBCCSRn[EDS] = 1), and
2. matches the next slot n (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 26-112. For the dynamic segment only those message buffers are considered,
that match the condition of at least one row of Table 26-113. 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 26-112
for the static segment and according to Table 26-113 for the dynamic segment are selected.
If there are multiple message buffer with highest priority, the message buffer with the lowest message
buffer number is selected. All message buffer which have the highest priority must have a consistent
channel assignment as specified in Section 26.6.7.2, Message Buffer Channel Assignment Consistency.
Depending on the message buffer channel assignment the same message buffer can be found for both
channel A and channel B. In this case, this message buffer is used as described in Section 26.6.3.1,
Individual Message Buffers.
Table 26-112. Message Buffer Search Priority (static segment)
Priority MTD LCKS CMT CCFM
1
1
Cycle Counter Filter Match, see Section 26.6.7.1, Message Buffer Cycle Counter Filtering.
Description Transition
(highest) 0 1011transmit 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
Table 26-113. Message Buffer Search Priority (dynamic segment)
Priority MTD LCKS CMT CCFM
1
1
Cycle Counter Filter Match, see Section 26.6.7.1, Message Buffer Cycle Counter Filtering.
Description Transition
(highest) 0 1011transmit buffer, matches cycle count, not locked and committed MA
1 0 0 n/a 1 receive buffer, matches cycle count, not locked SB
(lowest) 2 0 1 n/a 1 receive buffer, matches cycle count, locked SB
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