Time Triggered Communication Mode; Figure 197. Transmit Mailbox States - ST STM32F102 Series Reference Manual

Controller area network (bxCAN)
request while the mailbox is in transmit state can have two results. If the mailbox is
transmitted successfully the mailbox becomes empty with the TXOK bit set in the
CAN_TSR register. If the transmission fails, the mailbox becomes scheduled, the
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 197. Transmit mailbox states

21.4.2

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.
506/690
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
RQCP=0 Mailbox has
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