
Message Buffer Handling and Operations
MFR4200 Data Sheet, Rev. 0
Freescale Semiconductor
179
3.5.6.2.1
Single Transmit Message Buffer Data collection during Transmit Operation
The host can configure some message buffers of the CC as single transmit message buffers. If there is at
least one transmit message buffer configured, or the sync frame register value (see
Section 3.2.3.3.29,
“Sync Frame Register (SYNCFR)
”) is not 0x0, the CC can actively transmit frames out of the connected
FlexRay network.
To configure a single transmit message buffer, the following next steps must be performed.
1. Configure the message buffer as a transmit message buffer, in accordance with the configuration
procedure and principles.
2. Set the message buffer type bit (BT) to 0 — single transmit message buffer.
After a buffer is configured as a single transmit message buffer and a CC enters the normal mode of
operation, The host can start preparation and commitment of frames for transmission.
Figure 3-137
shows
an example of host and CC operation on a single transmit message buffer during frame transmission in
normal operation.
As shown in
Figure 3-137
, The host sends a lock request for a message buffer and always checks for the
lock request acknowledge bit LOCK to be a ‘1’ before it starts to update the message buffer content (see
Section 3.5.3.4, “Active Buffers Locking/Unlocking and Locking Timing
”
and
Section 3.2.3.6.3, “CHI
Error Register (CHIER)
” for more information).
After a transmit message buffer is locked, the host can update it, via the active transmit message buffer,
and can commit it to transmission by setting the BUFCMT bit to ‘1’ and unlocking the message buffer.
After transmission, the CC sets the IFLG bit of a message buffer, and clears BUFCMT. The CC changes
the VALID bit after transmission depending on the TT bit.