If both Rx FIFO and DMA are enabled (CAN_MCR[RFEN] and CAN_MCR[DMA] = 1)
the FlexCAN does not generate any FIFO interrupt. Bit 5 of the CAN_IFLAG1 register
still indicates "Frames Available in FIFO" and generates a DMA request. Bits 7, 6, 4-0
are unused.
For a combined interrupt where multiple MB interrupt sources are OR'd together, the
interrupt is generated when any of the associated MBs (or FIFO, if applicable) generates
an interrupt. In this case, the CPU must read the CAN_IFLAG registers to determine
which MB or FIFO source caused the interrupt.
The interrupt sources for Bus Off, Bus Off Done, Error, Wake Up, Tx Warning and Rx
Warning generate interrupts like the MB interrupt sources, and can be read from
CAN_ESR1 register. The Bus Off, Error, Tx Warning, and Rx Warning interrupt mask
bits are located in the CAN_CTRL1 Register; the Wake-Up interrupt mask bit is located
in the CAN_MCR.
50.5.12 Bus interface
The CPU access to FlexCAN registers are subject to the following rules:
• Unrestricted read and write access to supervisor registers (registers identified with
S/U in Table "Module Memory Map" in Supervisor Mode or with S only) results in
access error.
• Read and write access to implemented reserved address space results in access error.
• Write access to positions whose bits are all currently read-only results in access error.
If at least one of the bits is not read-only then no access error is issued. Write
permission to positions or some of their bits can change depending on the mode of
operation or transitory state. Refer to register and bit descriptions for details.
• Read and write access to unimplemented address space results in access error.
• Read and write access to RAM located positions during Low Power Mode results in
access error.
• It is possible for the RXIMR memory region to be considered as general purpose
memory and available for access. There are two ways of doing this:
a. If CAN_MCR[IRMQ] is cleared, the individual masks (RXIMR) are disabled. In
this case the RXIMR memory region is considered as general purpose memory.
b. If CAN_MCR[MAXMB] is programmed with a value smaller than the available
number of MBs, then the unused memory space can be used as general purpose
RAM space. Note that reserved words within RAM cannot be used. As an
example, suppose FlexCAN's RAM can support up to 16 MBs,
CAN_CTRL2[RFFN] is 0x0, and CAN_MCR[MAXMB] is programmed with
zero. The maximum number of MBs in this case becomes one. The RAM starts
Chapter 50 CAN (FlexCAN)
Kinetis KE1xF Sub-Family Reference Manual, Rev. 4, 06/2019
NXP Semiconductors
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