
Message Buffer Handling and Operations
MFR4200 Data Sheet, Rev. 0
Freescale Semiconductor
181
3.5.6.2.2
Doubled Buffer Data collection during Transmit Operation
The host can configure some message buffers of the CC as double transmit message buffers. If there is at
least one double transmit message buffer configured, then the CC can actively transmit frames out of the
connected FlexRay network.
To configure a double transmit message buffer (
Figure 3-138
), the follow steps must be performed.
1. Configure the even number message buffer as a transmit message buffer, in accordance with the
configuration procedure and principles.
2. Set the message buffer type bit BT (see
Section 3.4.1, “Message Buffer Control, Configuration
and Status Register
”) to 1 — host part buffer of double transmit message buffers (configuration is
copied to the CC part buffers automatically).
The
Figure 3-139
shows an example of a double transmit message buffer data collection during the state
driven transmit operation in normal operation.
The
Figure 3-140
shows an example of a doubled transmit message buffer data collection during the event
driven transmit operation.
NOTE
When the CC transmits a null frame, it does not change the BUFCSnR
registers of the buffers.
Host Operations with a Double Transmit Message Buffer during Transmission
The host can perform the following operations on a double transmit message buffer.
Lock buffer for reading and/or modifying.
Read message buffer slot status vector, data and configuration.
Write data.
Commit and unlock for transmission.
Main principles of the host operations with double transmit message buffers:
The host always operates with host part buffers.
The host can perform operations with host part buffers independent of CC transmit operations from
the CC part buffers.
Data exchange is based on access requests and acknowledge flags.
The host and the CC operate only with configured buffers that have frame ID field not equal to ‘0’.
The addresses of the host part buffers do not change during normal operation.
The host has read-only access to the CC part buffer BUFCSnR registers.
Buffer
number
(even)
Host Part Buffer n
Buffer
Number+1
(odd)
CC part Buffer n+1
BUFCS(n)
BUFCS(n+1)
Figure 3-138. Double Transmit Message Buffer Structure