NXP Semiconductors MPC5644A, Reference Manual, Page: 1559 / 1735

FlexRay Communication Controller (FlexRay)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 1559
Figure 33-131. Message transmission timing
Figure 33-132. Message transmission from HLck state with unlock
The amount of message data read from the FlexRay memory area and transferred to the FlexRay bus is
determined by the following three items
1. the message buffer segment that the message buffer is assigned to, as defined by the Message
Buffer Segment Size and Utilization Register (FR_MBSSUTR) .
2. the message buffer data field size, as defined by the related field of the Message Buffer Data Size
Register (FR_MBDSR)
3. the value of the PLDLEN field in the message buffer header field, as described in
Section 33.6.5.2.1, Frame header description ”
If a message buffer is assigned to message buffer segment 1, and PLDLEN > MBSEG1DS, then
2 * MBSEG1DS bytes will be read from the message buffer data field and zero padding is used for the
remaining bytes for the FlexRay bus transfer. If PLDLEN < MBSEG1DS, the CC reads and transfers
2*PLDLEN bytes. The same holds for segment 2 and MBSEG2DS.
33.6.6.2.6 Null frame transmission
A static slot with slot number S is assigned to the CC for channel A, if at least one transmit message buffer
is configured with the FR_MBFIDRn[FID] set to S and FR_MBCCFRn[CHA] set to 1. A Null Frame is
transmitted in the static slot S on channel A, if this slot is assigned to the CC for channel A, and all transmit
message buffers with FR_MBFIDRn[FID] = s and FR_MBCCFRn[CHA] = 1 are either not committed,
that is, FR_MBCCSRn[CMT] = 0, or locked by the application, that is, FR_MBCCSRn[LCKS] = 1, or the
cycle counter filter is enabled and does not match.
Additionally, the application can clear the commit bit of a message buffer that is in the CCMa state, which
is called
uncommit or transmit abort . This message buffer will be used for null frame transmission.
As a result of the message buffer search described in Section 33.6.7, Individual message buffer search ”,
the CC triggers the slot assigned transition SA for up to two transmit message buffers if at least one of the
conditions mentioned above is fulfilled for these message buffers. The transition SA changes the message
buffer states from either Idle to CCSa or from HLck to HLckCCSa. In each case, these message buffers
search[s+1]
MT
s
tar
t
MA
slot s
TX SU
CCMa
CCTx
slot s+1
Idle
MT
s
ta
rt
Idle
slot s+2
slot st
art
slot st
art
slot st
art
MT
s
tar
t
message transmit
SSS
CCSu
search[s+1]
M
T
st
ar
t
MT
s
tar
t
MA
slot s
TX
SSS
HLckCCMa CCTx
slot s+1
HLck
M
T s
tar
t
Idle
slot s+2
slot
s
tart
slot
s
tart
slot
s
tart
HU
CCMa
message transmit