• Scan all Tx Buffers with activated transmission request
• Tx Buffer with lowest Message ID gets highest priority and is transmitted next
3.5.5.7 Transmit Cancellation
The M_CAN supports transmit cancellation. This feature is especially intended for
gateway applications and AUTOSAR based applications. To cancel a requested
transmission from a dedicated Tx Buffer or a Tx Queue Buffer the Host has to write a 1
to the corresponding bit position (= number of Tx Buffer) of register TXBCR. Transmit
cancellation is not intended for Tx FIFO operation.
Successful cancellation is signalled by setting the corresponding bit of register TXBCF to
1.
In case a transmit cancellation is requested while a transmission from a Tx Buffer is
already ongoing, the corresponding TXBRP bit remains set as long as the transmission is
in progress. If the transmission was successful, the corresponding TXBTO and TXBCF
bits are set. If the transmission was not successful, it is not repeated and only the
corresponding TXBCF bit is set.
Note
In case a pending transmission is cancelled immediately before
this transmission could have been started, there follows a short
time window where no transmission is started even if another
message is also pending in this node. This may enable another
node to transmit a message which may have a lower priority
than the second message in this node.
3.5.5.8 Tx Event Handling
To support Tx event handling the M_CAN has implemented a Tx Event FIFO. After the
M_CAN has transmitted a message on the CAN bus, Message ID and timestamp are
stored in a Tx Event FIFO element. To link a Tx event to a Tx Event FIFO element, the
Message Marker from the transmitted Tx Buffer is copied into the Tx Event FIFO
element.
The Tx Event FIFO can be configured to a maximum of 32 elements. The Tx Event FIFO
element is described in Tx Event FIFO Element.
Chapter 3 Modular CAN (M_CAN)
MPC5777C Reference Manual Addendum, Rev. 1, 12/2015
Freescale Semiconductor, Inc. 113
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