Transmit Priority Determination; Transmission Using Transmit Buffers - Renesas RZ/A Series User Manual

RZ/A1L Group, RZ/A1LU Group, RZ/A1LC Group
21.7.1

Transmit Priority Determination

If transmit requests are issued from multiple buffers or from the queue on the same channel, transmit
priority is determined using one of the following methods.
The priority is determined by using one of the following methods.
• ID priority (TPRI bit = 0)
• Transmit buffer number priority (TPRI bit = 1)
All CAN channels use the setting of the TPRI bit in the RSCAN0GCFG register.
When the TPRI bit is set to 0, messages are transmitted according to the priority of stored message IDs.
ID priority conforms to the CAN bus arbitration specification defined in the CAN specifications. All
IDs of pending transmit messages are targets of priority determination, regardless of whether they are
stored in transmit buffers, transmit/receive FIFO buffers (set to transmit mode or gateway mode), or the
transmit queue. If even a single transmit queue is used, select ID priority. When transmit/receive FIFO
buffers are used, the oldest message in a FIFO buffer becomes the target of priority determination.
When a message is being transmitted from a transmit/receive FIFO buffer, the next message in the
FIFO buffer becomes the target of priority determination. When a transmit queue is used, all messages
in the transmit queue are targets of priority determination. If the same ID is set for two or more buffers,
the buffer with the smaller buffer number takes precedence.
When the TPRI bit is set to 1, the message in the transmit buffer with the minimum buffer number
among all buffers with a transmit request is transmitted first. When transmit/receive FIFO buffers are
linked to transmit buffers, transmit priority is determined according to linked transmit buffer numbers.
When messages are retransmitted due to an arbitration-lost or an error, transmit priority determination
is made again regardless of the TPRI bit.
21.7.2

Transmission Using Transmit Buffers

Setting the transmit request bit (TMTR bit in the RSCAN0TMCp register) in a transmit buffer to 1
(transmission is requested) allows transmission of data frames or remote frames.
The transmit result is shown by the TMTRF[1:0] flag in the corresponding RSCAN0TMSTSp register
(p = 0 to 31). When transmit completes successfully, the TMTRF[1:0] flag is set to 10
has been completed (without transmit abort request)) or 11
transmit abort request)).
21.7.2.1 Transmit Abort Function
With respect to transmit buffers for which the TMTRM bit in the RSCAN0TMSTSp register is set to 1
(a transmit request is present), when the TMTAR bit in the RSCAN0TMCp register is set to 1 (transmit
abort is requested), the transmit request is canceled. When transmit abort is completed, the
TMTRF[1:0] flag in the RSCAN0TMSTSp register is set to 01
and the transmit request is canceled (clearing the TMTRM bit to 0).
A message that is being transmitted or a message to be transmitted next according to the transmit
priority determination cannot be aborted. However, when an arbitration-lost or an error occurs during
transmission of a message for which the TMTAR bit is set to 1, retransmission is not performed.
R01UH0437EJ0600 Rev.6.00
Jan 29, 2021
(transmission has been completed (with
B
(transmit abort has been completed)
B
21. CAN Interface
(transmission
B
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