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FlexRay Communication Controller (FlexRay)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1569
Double transmit message buffers are used by the application to provide the CC with the message data to
be transmitted over the FlexRay Bus. The CC uses this message buffer to provide information to the
application about the transmission process, and status information about the slot in which message data
was transmitted.
In contrast to the single transmit message buffers, the application can provide new transmission data while
the transmission of the previously provided message data is running. This scheme is called double
buffering and can be considered as a FIFO of depth 2.
Double transmit message buffers are implemented by combining two individual message buffers that form
the two sides of an double transmit message buffer. One side is called the
commit side
and will be accessed
by the application to provide the message data. The other side is called the
transmit side
and is used by the
CC to transmit the message data to the FlexRay bus. The two sides are located in adjacent individual
message buffers. The message buffer that implements the commit side has an even message buffer number
2n. The transmit side message buffer follows the commit side message buffer and has the message buffer
number 2n+1. The basic structure and data flow of a double transmit message buffer is given in
.
Figure 33-140. Double transmit buffer structure and data flow
NOTE
Both the commit and the transmit side must be configured with identical
values except for the
Message Buffer Index Registers (FR_MBIDXRn)
.
33.6.6.4.1
Access regions
To certain message buffer fields, both the application and the CC have access. To ensure data consistency,
a message buffer locking scheme is implemented, which controls the exclusive access to the data, control,
and status bits of the message buffer.
The access scheme for double transmit message buffers is depicted in
. The given regions
represent fields that can be accessed from both the application and the CC and, thus, require access
restrictions. A description of the regions is given in
.
Commit Side
Transmit Side
Application
FlexRay Bus
MB# 2n
MB# 2n+1
Internal Message
Transfer
message data
message data
message data
Содержание MPC5644A
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