FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 26-107
buffer and triggers the status updated transition SU. With the SU transition, the controller sets the message
buffer interrupt flag MBCCSRn[MBIF] to indicate the successful message transmission.
Depending on the transmission mode flag MBCCFRn[MTM], the controller changes the commit flag
MBCCSRn[CMT] and the valid flag MBCCSRn[DVAL]. If the MBCCFRn[MTM] flag is negated, the
message buffer is in the event transmission mode. In this case, each committed message is transmitted only
once. The commit flag MBCCSRn[CMT] is cleared with the SU transition. If the MBCCFRn[MTM] flag
is asserted, the message buffer is in the state transmission mode. In this case, each committed message is
transmitted as long as the application provides new data or locks the message buffers. The controller will
not clear the MBCCSRn[CMT] flag at the end of transmission and will set the valid flag
MBCCSRn[DVAL] to indicate that the message will be transmitted again.
Message Buffer Status Update after Incomplete Message Transmission
The term incomplete message transmission refers to the fact that not all payload data that should be
transmitted were send to FlexRay bus. This may be caused by the following regular conditions in the
dynamic segment:
1. The transmission slot starts in a minislot with a minislot number greater than pLatestTx.
2. The transmission slot did not exist in the dynamic segment at all.
Additionally, an incomplete message transmission can be caused by internal communication errors. If
those error occur, the Protocol Engine Communication Failure Interrupt Flag PECF_IF is set in the
Protocol Interrupt Flag Register 1 (PIFR1).
In any of these two cases, the status of the message buffer is not changed at all with the SU transition. The
slot status field is not updated, the status and control flags are not changed, and the interrupt flag is not set.
Message Buffer Status Update after Null Frame Transmission
After the transmission of a null frame, the status of the message buffer that was used for the null frame
transmission is not changed at all. The slot status field is not updated, the status and control flags are not
changed, and the interrupt flag is not set.
26.6.6.3 Receive Message Buffers
The section provides a detailed description of the functionality of the receive message buffers.
A receive message buffer is used to receive a message from the FlexRay Bus based on individual filter
criteria. The controller uses the receive message buffer to provide the following data to the application
1. message data received
2. information about the reception process
3. status information about the slot in which the message was received
A individual message buffer with message buffer number n is configured as a receive message buffer by
the following configuration settings
• MBCCSRn[MBT] = 0 (single buffered message buffer)
• MBCCSRn[MTD] = 0 (receive message buffer)
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