ST72561J4-Auto datasheet(234/324 Pages) STMICROELECTRONICS

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beCAN controller (beCAN)

ST72561-Auto

234/324

Doc ID 12370 Rev 8

Figure 109. FIFO corruption

Workaround

To implement the workaround, use the following sequence to release the CAN receive FIFO.

This sequence replaces any occurrence of

CRFR |= B_RFOM;

Figure 110. Workaround 1

Explanation of workaround 1

First, we need to make sure no interrupt can occur between the test and the release of the

FIFO to avoid any added delay.

The workaround checks if the first two FIFO levels are already full (FMP = 2) as the problem

happens only in this case.

If FMP

≠ 2 we release the FIFO immediately, if FMP = 2, we monitor the reception status of

the cell.

The reception status is available in the CMSR register bit 5 (REC bit).

Note:

The REC bit was called RX in older versions of the datasheet.

●

If the cell is not receiving, then REC bit in CMSR is at 0, the software can release the

FIFO immediately: there is no risk.

●

If the cell is receiving, it is important to make sure the release of the mailbox will not

happen at the time when the received message is loaded into the FIFO.

Initial State

* pointer to next receive location

v pointer to next message to be released

---

When the FIFO is empty, v and * point to the same location

FIFO

Receive Message A

A- -

Receive Message B

AB -

Receive Message C

ABC

* does not move because FIFO is full (normal operation)

Release Message A

ABC

Release Message B

DB C

and Receive Message D

DB C

Normal operation

* Does not move, pointer corruption

Receive Message E

EBC

Release Message C

EBC

Release Message E

EBC

C released

* v

Release Message B

EBC

* v

* and v are not pointing to the same message

D is overwritten by E

FMP

the FIFO is empty

E released instead of B

if ((CRFR & 0x03) == 0x02)

while

((CMSR & 0x20) && (CDGR & 0x08))

{ };

CRFR |= B_RFOM;

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