60.5.5.4 Tx Queue

Tx Queue operation is configured by programming MCAN_TXBC.TFQM to ‘1’. Messages stored in the Tx Queue are transmitted starting with the message with the lowest Message ID (highest priority). In case that multiple Tx Queue buffers are configured with the same Message ID, the transmission order depends on numbers of buffers where messages were stored for transmission. As these buffer numbers depend on the then current states of the Put index, a prediction of the transmission order is not possible

New messages have to be written to the Tx Buffer referenced by the Put Index MCAN_TXFQS.TFQPI. The Put index always points to the free buffer of the Tx Queue with the lowest buffer number. In case that the Tx Queue is full (MCAN_TXFQS.TFQF = ‘1’), the Put Index is not valid and no further message should be written to the Tx Queue until at least one of the requested messages has been sent out or a pending transmission request has been cancelled.

The application may use register MCAN_TXBRP instead of the Put Index and may place messages to any Tx Buffer without pending transmission request.

A Tx Queue Buffer allocates Element Size 32-bit words in the Message RAM (see the table Tx Buffer/FIFO/Queue Element Size). Therefore the start address of the next available (free) Tx Queue Buffer is calculated by adding Tx FIFO/Queue Put Index MCAN_TXFQS.TFQPI (0…31) × Element Size to the Tx Buffer Start Address MCAN_TXBC.TBSA.