FlexRay Module (FLEXRAYV2)
MFR4300 Data Sheet, Rev. 3
176
Freescale Semiconductor
3.4.6.4.6
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 can not be locked by the application, i.e. the
HU
and
HL
transition do not exist. Therefore, refer to
Section 3.4.6.2.5, “Message Transmission”
3.4.6.4.7
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 3.4.6.2.7, “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.
3.4.7
Individual Message Buffer Search
This section provides a detailed description of the message buffer search algorithm.
The message buffer search checks all enabled individual message buffer to determine if a certain slot is
assigned to this node for transmission or if this node is subscribed to a certain slot for reception. The
message buffer search is a sequential algorithm and is started at the following protocol related events:
each NIT start
each slot start in the static frame segment
each minislot start in the dynamic frame segment
The search within the NIT searches for message buffers assigned or subscribed to slot 1. The search within
slot
n
searches for message buffers assigned or subscribed to slot
n+1
.
If the message buffer search is running while the next message buffer search start event appears, the
message buffer search is stopped and the Message Buffer Search Error Flag MSB_EF is set in the
CHI
Error Flag Register (CHIERFR)
. This appears only if the CHI frequency is to low to search through all
message buffers within the NIT or a minislot. The message buffer result is not defined in this case. For
more details see
Section 3.5.2, “Number of Usable Message Buffers”.
The filters criteria used for the message buffer search described in
Section 3.4.7.1, “Individual Message
Buffer Filtering
”. For double transmit message buffers only the transmit side is included in the search.
During the search, a list of all matching message buffers is created. If all message buffers assigned or
subscribed to the next slot are assigned to only one channel, then two lists of matching message buffer will
be created, one for each channel. If all message buffers assigned or subscribed to the next slot are assigned
to both channels, only one sorted list of matching message buffers is created.