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by hardware; the other is that the mailbox fails to transmit, the mailbox becomes
predetermined and the transmitting request is aborted.
Automatic retransmission is disabled
Generally, in time triggered communication mode, automatic retransmission
should be disabled.
In the mode that the automatic retransmission is disabled, the message is sent
only once, and no matter what the result is (success, error or arbitration loss),
the hardware will not transmit the message again automatically.
When the transmitting process is finished, set the REQCFLG bit of the
CAN_TXSTS register to 1, and the transmitting result will be on the TXSUSFLG,
ARBLSTFLG and TXERRFLG bits
Data receiving
Receive FIFO
CAN has two receive FIFOs, each FIFO has three mailboxes, the FMNUM[1:0]
bit of the register CAN_RXF reflects the number of messages currently stored;
set the RFOM bit to1 to release the output mailbox of receive FIFO; FFULLFLG
is the full state flag bit; FOVRFLG is overrun state flag bit.
Receive FIFO state conversion
At the beginning FIFO is in empty state, and after receiving the message, it will
become registered.
When FIFO is in registered state and three mailboxes are full, after receiving
next effective message, it will enter the overrun state, and there are two
situations for loss of messages in overrun state:
If FIFO lock function is disabled, the finally received message will be
covered by new message
If FIFO lock function is enabled, the newly received message will be
discarded
Filtering mechanism
Function of the filter: The receiving node decides whether the message is
needed according to the message identifier, and only the required message will
be received after filtering. CAN controller has
28
filter groups.
Bit width
Each group of filters can configure two kinds of bit width.