FlexRay Communication Controller (FlexRAY)
PXN20 Microcontroller Reference Manual, Rev. 1
26-122 Freescale Semiconductor
Figure 26-135. Internal Message Transfer in Immediate Commit Mode
26.6.6.4.6 Message Transmission
For double transmit message buffers, the message buffer search checks only the transmit side part. The
internal scheduling ensures, that the internal message transfer is stopped on the message buffer search start.
Thus, the transmit side of message buffer, that is not in its transmission or status update slot, is always in
the Idle state.
The message transmit behavior and transmission state changes of the transmit side of a double transmit
message buffer are the same as for single buffered transmit buffers, except that the transmit side of double
buffers cannot be locked by the application, that is, the HU and HL transition do not exist. Therefore, refer
to Section 26.6.6.2.5, Message Transmission.
26.6.6.4.7 Message Buffer Status Update
The message buffer status update behavior of the transmit side of a double transmit message buffer is the
same as for single transmit message buffers which is described in Section 26.6.6.2.7, Message Buffer
Status Update.
Additionally, the slot status field of the commit side is update after the update of the slot status field of the
transmit side, even if the commit side is locked by the application. This is implemented to provide the slot
status of the most recent transmission slot.
26.6.7 Individual Message Buffer Search
This section provides a detailed description of the message buffer search algorithm.
The message buffer search determines for each enabled channel if a slot s in a communication cycle c is
assigned for frame or null frame transmission or if it is subscribed for frame reception on that channel.
The message buffer search is a sequential algorithm which is invoked at the following protocol related
events:
1. NIT start
2. slot start in the static segment
3. minislot start in the dynamic segment
Idle
CommitTransmit
Idle
HL
HLck
Side Side
slot s slot s+1 slot s+2
search[s+1]
slot start
slot start
slot start
HU
CCITx
Idle
IS
CCITx
IE
Idle
HL
HLck
HU
Idle
CCITx
Idle
IS
CCITx
IE
Idle
Idle
internal message transfer
overwrites non-transmitted message
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