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FlexRay Communication Controller (FlexRay)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1577
Immediate commit mode
The intention of the immediate commit mode is to transmit the
latest
data provided by the application.
This implies that it is not guaranteed that each provided message will be transmitted at least once.
The immediate commit mode is configured by setting the message buffer commit mode bit MCM in the
Message Buffer Configuration, Control, Status Registers (FR_MBCCSRn)
.
In this mode, the internal message transfer from the commit side to the transmit side is started for one
double transmit message buffer when all of the following conditions are fulfilled
1. the commit side is in the Idle state
2. the commit site message data are valid, that is, FR_MBCCSR(2n)[CMT] = 1
3. the transmit side is in one of the states Idle, CCSa, or CCMa
It is not checked whether the transmit side contains no valid message data or valid message data were
transmitted at least once. If message data are valid and not transmitted, they may be overwritten.
An example of a streaming commit mode state change diagram is given in
. In this example,
both the commit and the transmit side do not contain valid message data, and the application provides two
messages and the first message is gets overwritten. The message buffer does not match the next slot.
Figure 33-145. Internal message transfer in immediate commit mode
33.6.6.4.6
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 can not be locked by the application, that is, the HU and HL transition do not exist. Therefore, refer
to
Section 33.6.6.2.5, Message transmission”
.
33.6.6.4.7
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 33.6.6.2.7, Message buffer status
.
Idle
Commit
Tr
a
n
s
m
it
Idle
HL
HLck
Side
Sid
e
slot s
slot s+1
slot s+2
search[s+1]
slot
st
art
s
lot
st
art
s
lot
st
art
HU
Idle
IS
CCITx
IE
Idle
HL
HLck
HU
Idle
Idle
IS IE
Idle
Idle
internal message transfer
overwrites non-transmitted message
CCITx
CCITx
CCITx
Содержание MPC5644A
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