STM32H723ZG: FDCAN frame sent successfully but not received (Internal Loopback)

[mpek29]

Hi everyone,

I'm having a hard time with the FDCAN on a NUCLEO-H723ZG. I’ve tried several setups (external with transceivers, external loopback with wires), but I’ve stripped everything back to Internal Loopback mode on FDCAN1 to simplify things.

Current situation: I can actually see that the frame is sent successfully (no TX errors), but the receive interrupt/FIFO never triggers. It’s like the frame is going out into the void and not looping back into the RX FIFO.

I'm using the HAL drivers.

Here are the errors/status I'm getting via printf:

Full code is available here: https://github.com/mpek29/FDCAN-NUCLEO-H723ZG

Has anyone experienced this "TX works but RX fails" issue on the H7 series?

Thanks for any help! mpek29

[mƎALLEm]

Hello @mpek29 and welcome to the ST community,

I detected many issues in your project:

1- You set the FDCAN peripheral to send Classic frame but you send an FDCAN frame with BRS OFF!:

 hfdcan1.Init.FrameFormat = FDCAN_FRAME_CLASSIC;

 TxHeader.BitRateSwitch = FDCAN_BRS_OFF;
 TxHeader.FDFormat = FDCAN_FD_CAN;

It should be:

 TxHeader.BitRateSwitch = FDCAN_BRS_OFF;
 TxHeader.FDFormat = FDCAN_CLASSIC_CAN;

2- You didn't set tRxFIFO0 element size nor the Standard filter: number:

 hfdcan1.Init.StdFiltersNbr = 0;
 hfdcan1.Init.RxFifo0ElmtsNbr = 0;

They should be set at least to 1:

 hfdcan1.Init.StdFiltersNbr = 1;
 hfdcan1.Init.RxFifo0ElmtsNbr = 1;

3- Avoid setting 1TQ for one of the time segments:

 hfdcan1.Init.NominalTimeSeg2 = 1;

Try the following bit timing parameters @1Mb/s:

 hfdcan1.Init.NominalPrescaler = 3;
 hfdcan1.Init.NominalTimeSeg1 = 12;
 hfdcan1.Init.NominalTimeSeg2 = 3;

Hope that helps.