PXS20RM Datasheet, PDF (832/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

FlexRay Communication Controller
MA
HU
TX
HLck
HLckCCMa
MT ^start
MT ^start
search[s+1]
slot s
CCMa
CCTx
message transmit
slot s+1
SSS
Idle
MT ^start
slot s+2
Figure 26-132. 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 26.6.5.2.1, 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.
26.6.6.2.6 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,
i.e FR_MBCCSRn[CMT] = 0, or locked by the application, i.e. 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 26.6.7, 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
will be used for null frame transmission in the next slot. A message buffer timing and state change diagram
for null frame transmission from Idle state is given in Figure 26-133.
26-120
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor