66.5.5 Tx Handling

The Tx Handler handles transmission requests for the dedicated Tx Buffers, the Tx FIFO, and the Tx Queue. It controls the transfer of transmit messages to the CAN Core, the Put and Get Indices, and the Tx Event FIFO. Up to 32 Tx Buffers can be set up for message transmission. The CAN mode for transmission (Classic CAN or CAN FD) can be configured separately for each Tx Buffer element. The Tx Buffer element is described in Tx Buffer Element. The following table describes the possible configurations for frame transmission.

Table 66-5. Possible Configurations for Frame Transmission
MCAN_CCCR Tx Buffer Element Frame Transmission
BRSE FDOE FDF BRS
ignored 0 ignored ignored Classic CAN
0 1 0 ignored Classic CAN
0 1 1 ignored FD without bit rate switching
1 1 0 ignored Classic CAN
1 1 1 0 FD without bit rate switching
1 1 1 1 FD with bit rate switching
Note: AUTOSAR requires at least three Tx Queue Buffers and support of transmit cancellation.

The Tx Handler starts a Tx scan to check for the highest priority pending Tx request (Tx Buffer with lowest Message ID) when MCAN_TXBRP is updated, or when a transmission has been started.