updates both the FIFO output with the next message (if FIFO is not empty) and the
CAN_RXFIR register with the attributes of the new message. If there are more messages
stored in the FIFO, the CAN_IFLAG1[BUF5I] will be re-asserted and another DMA
request is issued. Otherwise, the flag remains negated.
NOTE
CAN_RXFIR register contents cannot be read after DMA
completes the FIFO read. The IDHIT information is also
available in the C/S word at address 0x080 (see
.
The CAN_IFLAG1[BUF6I] and CAN_IFLAG1[BUF7I] are not used when the DMA
feature is enabled.
When FlexCAN is working with DMA, the CPU does not receive any Rx FIFO
interruption and must not clear the related IFLAGs. In addition, the related IMASKs are
not used to mask the generation of DMA requests.
43.5.7.2 Clear FIFO Operation
When CAN_MCR[RFEN] is asserted, the clear FIFO operation is a feature used to empty
FIFO contents. With CAN_MCR[RFEN] asserted the Clear FIFO occurs when the CPU
writes 1 in CAN_IFLAG1[BUF0I]. This operation can only be performed in Freeze
Mode and is blocked by hardware in other modes. This operation does not clear the FIFO
IFLAGs, consequently the CPU must service all FIFO IFLAGs before execute the clear
FIFO task.
When Rx FIFO is working with DMA, the clear FIFO operation clears the
CAN_IFLAG1[BUF5I] and the DMA request is canceled.
CAUTION
Clear FIFO operation does not clear IFLAGs, except when
CAN_MCR[DMA] is asserted, in this case only the
CAN_IFLAG1[BUF5I] is cleared.
43.5.8 CAN protocol related features
This section describes the CAN protocol related features.
Chapter 43 Flex Controller Area Network (FlexCAN)
KV4x Reference Manual, Rev. 2, 02/2015
Freescale Semiconductor, Inc.
Preliminary
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