FlexRay Communication Controller (FLEXRAY)
MPC5510 Microcontroller Family Reference Manual, Rev. 1
Freescale Semiconductor
30-101
Preliminary
30.6.6.2.4
Transmit Message Setup
To transmit a message over the FlexRay bus, the application writes the message data into the message
buffer data field and sets the commit bit CMT in the
Message Buffer Configuration, Control, Status
. The physical access to the message buffer data field is described in
Section 30.6.3.1, “Individual Message Buffers
”.
, the application shall write to the message buffer data field and change the
commit bit CMT only if the transmit message buffer is in one of the states HDis, HDisLck, HLck,
HLckCCSa, HLckCCMa, or HLckCCMa. The application can change the state of a message buffer if it
issues the appropriate commands shown in
. The state change is indicated through the
MBCCSRn.EDS and MBCCSRn.LCKS status bits.
If the transmit message buffer enters one of the states HDis, HDisLck, HLck, HLckCCSa, HLckCCMa, or
HLckCCMa the MBCCSRn.DVAL flag is negated.
30.6.6.2.5
Message Transmission
As a result of the message buffer search described in
Section 30.6.7, “Individual Message Buffer Search
the FlexRay block triggers the message available transition MA for up to two transmit message buffers.
This changes the message buffer state from Idle to CCMa and the message buffers can be used for message
transmission in the next slot.
The FlexRay block transmits a message from a message buffer if both of the following two conditions are
fulfilled at the start of the transmission slot:
1. the message buffer is in the message available state CCMa
2. the message data are still valid, i.e. MBCCSRn.CMT = 1
In this case, the FlexRay block triggers the TX transition and changes the message buffer state to CCTx.
A transmit message buffer timing and state change diagram for message transmission is given in
. In this example, the message buffer with message buffer number n is Idle at the start of the
search slot, matches the slot and cycle number of the next slot, and message buffer data are valid, i.e.
MBCCSRn.CMT = 1.
module internal
Idle, HLck
MA > SA
Message Available > Slot Assigned
CCMa
TX > STS
TX > DSS
Transmission Slot Start > Static Slot Start
Transmission Slot Start > Dynamic Slot Start
Table 30-96. Single Transmit Message Buffer Transition Priorities
State
Priorities
Description