Module Operation
1251
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
FlexRay Module
Access to the message buffers stored in the message RAM is done under control of the message handler
state machine. This avoids conflicts between accesses of the two protocol controllers and the host CPU to
the message RAM.
Frame IDs of message buffers assigned to the static segment have to be in the range from 1 to
GTU7.NSS(9-0) as configured in the GTU configuration register 7. Frame IDs of message buffers
assigned to the dynamic segment have to be in the range from GTU7.NSS(9-0) + 1 to 2047.
Received messages with no matching dedicated receive buffer (static or dynamic segment) are stored in
the receive FIFO (if configured) if they pass the FIFO rejection filter.
26.2.12.1 Reconfiguration of Message Buffers
In case that an application needs to operate with more than 128 different messages, static and dynamic
message buffers may be reconfigured during FlexRay operation. This is done by updating the header
section of the corresponding message buffer through Input Buffer registers WRHS1,2,3.
Reconfiguration has to be enabled through control bits MRC.SEC(1-0) in the Message RAM Configuration
register.
If a message buffer has not been transmitted / updated from a received frame before reconfiguration
starts, the corresponding message is lost.
The point in time when a reconfigured message buffer is ready for transmission / reception according to
the reconfigured frame ID depends on the current state of the slot counter when the update of the header
section has completed. Therefore it may happen that a reconfigured message buffer is not transmitted /
updated from a received frame in the cycle where it was reconfigured.
The Message RAM is scanned according to
Table 26-11. Scan of Message RAM
Start of Scan in Slot
Scan for Slots
1
2...15, 1 (next cycle)
8
16...23, 1 (next cycle)
16
24...31, 1 (next cycle)
24
32...39, 1 (next cycle)
....
...
A Message RAM scan is terminated with the start of NIT irrespective of it’s completion. The scan of the
Message RAM for slots 2 to 15 starts at the beginning of slot 1 of the current cycle. The scan of the
Message RAM for slot 1 is done in the cycle before by checking in parallel to each scan of the Message
RAM whether there is a message buffer configured for slot 1 of the next cycle.
The number of the first dynamic message buffer is configured by MRC.FDB(7-0) in the Message RAM
Configuration register. In case a Message RAM scan starts while the Communication Controller is in
dynamic segment, the scan starts with the message buffer number configured by MRC.FDB(7-0).
In case a message buffer needs to be reconfigured to be used in slot 1 of the next cycle, the following has
to be considered:
•
If the message buffer to be reconfigured for slot 1 is part of the Static Buffers, it will only be found if it
is reconfigured before the last Message RAM scan in the static segment of the current cycle evaluates
this message buffer.
•
If the message buffer to be reconfigured for slot 1 is part of the Dynamic Buffers, it will be
found if it is reconfigured before the last Message RAM scan in the current cycle evaluates this
message buffer.
•
The start of NIT terminates the Message RAM scan. In case the Message RAM scan has not
evaluated the reconfigured message buffer until this point in time, the message buffer will not be
considered for the next cycle.