Module Operation
1246
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
FlexRay Module
26.2.9 Transmit Process
26.2.9.1 Static Segment
For the static segment, if there are several messages pending for transmission, the message with the
frame ID corresponding to the next sending slot is selected for transmission.
The data section of transmit buffers assigned to the static segment can be updated until the end of the
preceding time slot. This means that a transfer from the input buffer has to be started by writing to the
Input Buffer Command Request Register latest at this time.
26.2.9.2 Dynamic Segment
In the dynamic segment, if several messages are pending, the message with the highest priority (lowest
frame ID) is selected next. In the dynamic segment different slot counter sequences on channel A and
channel B are possible (concurrent sending of different frame IDs on both channels).
The data section of transmit buffers assigned to the dynamic segment can be updated until the end of the
preceding slot. This means that a transfer from the input buffer has to be started by writing to the Input
Buffer Command Request Register latest at this time.
The start of latest transmit configured by MHDC.SLT(12-0) in the MHD configuration register 1 defines the
maximum minislot value allowed before inhibiting new frame transmission in the dynamic segment of the
current cycle.
26.2.9.3 Transmit Buffers
Communication Controller message buffers can be configured as transmit buffers by programming bit
CFG in the header section of the corresponding message buffer to 1 in WRHS1.
There exist the following possibilities to assign a transmit buffer to the communication controller channels:
•
Static segment:
–
channel A or channel B
–
channel A and channel B
•
Dynamic segment:
–
channel A or channel B
Message buffer 0 or 1 is dedicated to hold the startup frame, the sync frame, or the designated single slot
frame as configured by SUCC1.TXST, SUCC1.TXSY, and SUCC1.TSM in the SUC Configuration register
1. In this case it can be reconfigured in DEFAULT_CONFIG or CONFIG state only. This ensures that any
node transmits at most one startup / sync frame per communication cycle. Transmission of startup / sync
frames from other message buffers is not possible.
All other message buffers configured for transmission in static or dynamic segment are reconfigurable
during runtime depending on the configuration of MRC.SEC(1-0). Due to the organization of the data
partition in the message RAM (reference by data pointer), reconfiguration of the configured payload length
and the data pointer in the header section of a message buffer may lead to erroneous configurations.
If a message buffer is reconfigured (header section updated) during runtime, it may happen that this
message buffer is not sent out in the currently active communication cycle.
The communication controller does not have the capability to calculate the header CRC. The host is
supposed to provide the header CRCs for all transmit buffers. If network management is required the host
has to set the PPIT bit in the header section of the corresponding message buffer to 1 and write the
network management information to the data section of the message buffer.
The payload length field configures the data payload length in 2-byte words. If the configured payload
length of a static transmit buffer is shorter than the payload length configured for the static segment by
MHDC.SFDL(6-0) in the message handler configuration register 1, the communication controller generates
padding bytes to ensure that frames have proper physical length. The padding pattern is logical 0.