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When the Abort feature is enabled (CAN_MCR[AEN] is asserted), after the Interrupt
Flag is asserted for a Mailbox configured as transmit buffer, the Mailbox is blocked.
Therefore the CPU is not able to update it until the Interrupt Flag is negated by CPU.
This means that the CPU must clear the corresponding IFLAG bit before starting to
prepare this MB for a new transmission or reception.
43.5.2 Arbitration process
The arbitration process scans the Mailboxes searching the Tx one that holds the message
to be sent in the next opportunity. This Mailbox is called the arbitration winner.
The scan starts from the lowest number Mailbox and runs toward the higher ones.
The arbitration process is triggered in the following events:
• From the CRC field of the CAN frame. The start point depends on the
CAN_CTRL2[TASD] field value.
• During the Error Delimiter field of a CAN frame.
• During the Overload Delimiter field of a CAN frame.
• When the winner is inactivated and the CAN bus has still not reached the first bit of
the Intermission field.
• When there is CPU write to the C/S word of a winner MB and the CAN bus has still
not reached the first bit of the Intermission field.
• When CHI is in Idle state and the CPU writes to the C/S word of any MB.
• When FlexCAN exits Bus Off state.
• Upon leaving Freeze mode or Low Power mode.
If the arbitration process does not manage to evaluate all Mailboxes before the CAN bus
has reached the first bit of the Intermission field the temporary arbitration winner is
invalidated and the FlexCAN will not compete for the CAN bus in the next opportunity.
The arbitration process selects the winner among the active Tx Mailboxes at the end of
the scan according to both CAN_CTRL1[LBUF] and CAN_MCR[LPRIOEN] bits
settings.
Freescale Semiconductor, Inc.
KV4x Reference Manual, Rev. 2, 02/2015
Preliminary
Chapter 43 Flex Controller Area Network (FlexCAN)
1131
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