Time Triggered Communication Mode; Reception Handling; Figure 125. Transmit Mailbox States - ST STM32F101 Series Reference Manual

Controller area network (bxCAN)
transmission is aborted and becomes empty with TXOK cleared. In all cases the mailbox
will become empty again at least at the end of the current transmission.
Non-automatic retransmission mode
This mode has been implemented in order to fulfil the requirement of the Time Triggered
Communication option of the CAN standard. To configure the hardware in this mode the
NART bit in the CAN_MCR register must be set.
In this mode, each transmission is started only once. If the first attempt fails, due to an
arbitration loss or an error, the hardware will not automatically restart the message
transmission.
At the end of the first transmission attempt, the hardware considers the request as
completed and sets the RQCP bit in the CAN_TSR register. The result of the transmission is
indicated in the CAN_TSR register by the TXOK, ALST and TERR bits.

Figure 125. Transmit mailbox states

14.5.2

Time triggered communication mode

In this mode, the internal counter of the CAN hardware is activated and used to generate the
Time Stamp value stored in the CAN_RDTxR/CAN_TDTxR registers, respectively (for Rx
and Tx mailboxes). The internal counter is captured on the sample point of the Start Of
Frame bit in both reception and transmission.
14.5.3

Reception handling

For the reception of CAN messages, three mailboxes organized as a FIFO are provided. In
order to save CPU load, simplify the software and guarantee data consistency, the FIFO is
280/501
EMPTY
RQCP=X
TXOK=X
TXRQ=1
TME = 1
ABRQ=1
EMPTY
RQCP=1
TXOK=0
TME = 1
Transmit failed * NART
EMPTY
Transmit succeeded
RQCP=1
TXOK=1
TME = 1
PENDING
Mailbox has
RQCP=0
TXOK=0
highest priority
TME = 0
Mailbox does not
have highest priority
ABRQ=1
CAN Bus = IDLE
TRANSMIT
Transmit failed * NART
RQCP=0
TXOK=0
TME = 0
RM0008
SCHEDULED
RQCP=0
TXOK=0
TME = 0