PXR40RM Datasheet, PDF (686/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

FlexRay Communication Controller (FLEXRAY)
22.6.6.2.5 Message Transmission
As a result of the message buffer search described in Section 22.6.7, Individual Message Buffer Search,
the controller triggers the message available transition MA for up to two transmit message buffers. This
changes the message buffer state from Idle to CCMa and the message buffers can be used for message
transmission in the next slot.
The controller transmits a message from a message buffer if both of the following two conditions are
fulfilled at the start of the transmission slot:
1. the message buffer is in the message available state CCMa
2. the message data are still valid, i.e. MBCCSRn[CMT] = 1
In this case, the controller triggers the TX transition and changes the message buffer state to CCTx. A
transmit message buffer timing and state change diagram for message transmission is given in
Figure 22-121. In this example, the message buffer with message buffer number n is Idle at the start of the
search slot, matches the slot and cycle number of the next slot, and message buffer data are valid, i.e.
MBCCSRn[CMT] = 1.
Idle
MA
MT ^start
MT ^start
search[s+1]
TX
CCMa
CCTx
message transmit
slot s
slot s+1
Figure 22-121. Message Transmission Timing
SSS SU
CCSu ^Idle
MT ^start
slot s+2
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 22-122. Message Transmission from HLck state with unlock
The amount of message data read from the flexray memory and transferred to the FlexRay bus is
determined by the following three items:
• The message buffer segment that the message buffer is assigned to, as defined by the Message
Buffer Segment Size and Utilization Register (MBSSUTR).
• The message buffer data field size, as defined by the related field of the Message Buffer Data Size
Register (MBDSR)
• The value of the PLDLEN field in the message buffer header field, as described in
Section 22.6.5.2.1, Frame Header Description
22-102
PXR40 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor