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1. This is a don't care condition.
2. Matched in MB "None" means that the frame has not matched any MB (free-to-receive or non–free-to-receive).
3. This is a forbidden condition.
4. Matched in MB "Free" means that the frame matched at least one MB free-to-receive regardless of whether it has matched
MBs non-free-to-receive.
5. Matched in FIFO "None" means that the frame has not matched any filter in FIFO. It is as if the FIFO didn't exist
(CTRL2[RFEN]=0).
6. Matched in FIFO "Not full" means that the frame has matched a FIFO filter and has empty slots to receive it.
7. Matched in FIFO "Full" means that the frame has matched a FIFO filter but couldn't store it because it has no empty slots
to receive it.
If a non-safe mailbox inactivation (see
process and the mailbox inactivated is the temporary matching winner, then the
temporary matching winner is invalidated. The matching elements scan is not stopped nor
restarted—it continues normally. The consequence is that the current matching process
works as if the matching elements compared before the inactivation did not exist,
therefore a message may be lost.
Suppose, for example, that the FIFO is disabled, IRMQ is enabled, there are two MBs
with the same ID, and FlexCAN starts receiving messages with that ID. Let us say that
these MBs are the second and the fifth in the array. When the first message arrives, the
matching algorithm finds the first match in MB number 2. The code of this MB is
EMPTY, so the message is stored there. When the second message arrives, the matching
algorithm finds MB number 2 again, but it is not "free-to-receive", so it keeps looking,
finds MB number 5 and stores the message there. If yet another message with the same
ID arrives, the matching algorithm finds out that there are no matching MBs that are
"free-to-receive", so it decides to overwrite the last matched MB, which is number 5. In
doing so, it sets the CODE field of the MB to indicate OVERRUN.
The ability to match the same ID in more than one MB can be exploited to implement a
reception queue (in addition to the full featured FIFO) to allow more time for the CPU to
service the MBs. By programming more than one MB with the same ID, received
messages are queued into the MBs. The CPU can examine the Time Stamp field of the
MBs to determine the order in which the messages arrived.
Matching to a range of IDs is possible by using ID acceptance masks. FlexCAN supports
individual masking per MB (see the description of
Rx Individual Mask registers (RXIM
). During the matching algorithm, if a mask bit is asserted, then the
corresponding ID bit is compared. If the mask bit is negated, the corresponding ID bit is a
"don't care". Note that the Individual Mask Registers are implemented in RAM, so they
are not initialized out of reset. Also, they can only be programmed when the module is in
Freeze mode; otherwise, they are blocked by hardware.
FlexCAN also supports an alternate masking scheme with only four mask registers
(RXFGMASK, RXMGMASK, RX14MASK, and RX15MASK) for backwards
compatibility with legacy applications. This alternate masking scheme is enabled when
the IRMQ bit in the MCR register is negated.
Functional description
MWCT101xS Series Reference Manual, Rev. 3, 07/2019
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NXP Semiconductors
Содержание MWCT101 S Series
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Страница 78: ...Pinout diagrams MWCT101xS Series Reference Manual Rev 3 07 2019 78 NXP Semiconductors...
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