34.6.6.4 Tx Queue

Tx Queue operation is configured by programming 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 Queue Buffers are configured with the same Message ID, the Queue Buffer with the lowest buffer number is transmitted first.

New messages have to be written to the Tx Buffer referenced by the Put Index TXFQS.TFQPI. An Add Request cyclically increments the Put Index to the next free Tx Buffer. In case that the Tx Queue is full (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 canceled.

The application may use register 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 (refer to Table 34-7). Therefore the start address of the next available (free) Tx Queue Buffer is calculated by adding Tx FIFO/Queue Put Index TXFQS.TFQPI (0…31) • Element Size to the Tx Buffer Start Address TXBC.TBSA.