False Positive Acceptance with CAN Rx FIFO?

[gbrowne]

Hello.

One of our QA engineers picked up on false positives in the CAN message acceptance today.

We set a FLEXCAN_MSG_ID_STD global mask to 0x7FF (i.e. exact match) using FLEXCAN_DRV_SetRxFifoGlobalMask() - I can verify that the value of CAN0->RXFGMASK is properly set to 0x1FFC0000.

Then the filter is set to 0x51C using FLEXCAN_DRV_ConfigRxFifo() with FLEXCAN_RX_FIFO_ID_FORMAT_A format.

However, messages with a CAN ID of 0x11C are being accepted using FLEXCAN_DRV_RxFifoBlocking().  So it looks like only part of the mask is working (potentially)...

Any ideas what I may be missing?

Thanks,

-Greg

[PetrS · Accepted solution]

Hi,

mask within a RXFGMASK should be shifted left by 1 bit as you can see from Table 53-7

so, to have exact match you need to set RXFGMASK = 0x3FF80000.

Most probably the driver function does not shift the value properly.

With the RXFGMASK = 0x1FFC0000  the MSB of the ID is don't care, that's the reason you received ID 0x11C too.

BR, Petr

[gbrowne]

Hi Petr.

Yes!  Looks like you nailed it - the FLEXCAN_HAL_SetRxFifoGlobalStdMask() and FLEXCAN_HAL_SetRxFifoGlobalExtMask() methods under the FLEXCAN_DRV_SetRxFifoGlobalMask() method are not implemented properly (shifting and masking).

Great catch.  Fixing that solved my issue - thanks a lot!

-Greg