mfr4200 Freescale Semiconductor, Inc, mfr4200 Datasheet - Page 177

• Manufacturer Part Number: mfr4200
• Description: Flexray Communication Controllers
• Manufacturer: Freescale Semiconductor, Inc

principles. The CC handles transmit operations differently during the static and dynamic segments of
transmission; it also handles single and double transmit message buffers differently. For transmission, the
CC uses data from configured and committed transmit message buffers only.
The host submits a frame for transmission by committing a message buffer for transmission (BUFCMT
bit) and by subsequent unlocking of the transmit message buffer. The transmit message buffer remains
valid for transmission until its VALID bit = 1.
To prepare a transmit message buffer for transmission, the following steps must be performed.
Commitment-to-transmission time for single and double transmit message buffers:
To transmit a frame in slot n, the host must commit and unlock the buffer:
Static segment:
For the static segment, if there are several frames pending for transmission, the frame with the ID
corresponding to the next sending slot is selected for transmission. The CC checks other filtering fields of
those messages. If several frames are suitable for current static slot transmission, the CC performs an
internal arbitration.
The CC transmission procedure is described in detail in the frame processing section of the PWD. The
most important points are as follows.
The CC changes the following bits, if a message from a message buffer has been sent.
Freescale Semiconductor
1. Configure the message buffer as a transmit message buffer in accordance with the buffer
2. Lock the corresponding message buffer, to make it accessible in the active transmit message
3. Write/read the active transmit message buffer to change or update the message buffer content.
4. Commit the message buffer for transmission, by setting the BUFCMT bit to ‘1’.
5. Unlock the message buffer.
•
•
•
•
•
•
configuration procedure and principles.
buffer. Buffer locking must be done in accordance with the locking/unlocking procedure and
principles
Static segment transmit message buffer: 4 µT before the beginning of slot n-1 or the network idle
time (NIT).
Dynamic segment transmit message buffer: 4 µT before the beginning of slot n-1 or the network
idle time (NIT).
Only valid frames (VALID bit = 1) can be transmitted by the CC.
If there are valid frames with the same frame ID, the CC checks their filter fields. If two or more
of them match the conditions of the transmit slot, the message buffer with the lowest message
buffer number wins the internal arbitration.
If two buffers are assigned to the same static slot but to different transmission channels, the CC
transmits them simultaneously on assigned channels during transmission of that static slot.
If a message buffer was committed for transmission (BUFCMT = 1) it becomes valid (VALID = 1)
after buffer unlock operation, and the host cannot lock it until it is transmitted at least once.
MFR4200 Data Sheet, Rev. 0
Message Buffer Handling and Operations
177