ST72561 datasheet(189/262 Pages) STMICROELECTRONICS

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ST72561

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beCAN CONTROLLER (Cont’d)

10.9.7 BeCAN Cell Limitations

10.9.7.1 FIFO Corruption

FIFO corruption occurs in the following case:

WHEN the beCAN RX FIFO already holds 2 mes-

sages (i.e. FMP==2)

AND the application releases the FIFO (with

the instruction CRFR=B_RFOM;)

WHILE the beCAN requests the transfer of a new

receive message into the FIFO (this lasts one CPU

cycle)

THEN the internal FIFO pointer is not updat-

BUT the FMP bits are updated correctly

As the FIFO pointer is not updated correctly, this

causes the last message received to be overwrit-

ten by any incoming message. This means one

message is lost as shown in the example in Figure

109. The beCAN will not recover normal operation

until a device reset occurs.

Figure 109. FIFO Corruption.

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

AB C

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

Release Message A

AB C

Release Message B

DB C

and Receive Message D

DB C

Normal operation

* does not move, pointer corruption

Receive Message E

EB C

Release Message C

EB C

Release Message E

EB C

C released

* v

Release Message B

EB C

* 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

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