FDCAN FDCAN_RxHeaderTypeDef.data_length is always 0

[cstyx]

Describe the set-up

• STM32 NUCLEO-H723 board
• STM32 CubeIDE 1.15.1 Build: 21094_20240412_1041 (UTC)
• H723 firmware FW_H7 V1.11.2

Describe the bug

• FDCAN_RxHeaderTypeDef property data_length is always 0 when receiving FDCAN messages

How To Reproduce

• set up board for FDCAN (no bit rate switching)
• receive a CAN-message without any data data_length == 0 -> OK
• receive a CAN-message with some data (e.g. 8Bytes) the property data_length == 0 -> FAIL
• probably CAN driver stm32h7xx_hal_fdcan.c added right shift 16 at line 3074 and 3199

  
  /* Retrieve DataLength */
  pRxHeader->DataLength = ((*RxAddress & FDCAN_ELEMENT_MASK_DLC) >> 16U);

To reproduce this issue the test project attached at https://github.com/STMicroelectronics/STM32CubeH7/issues/292 can be used

[ALABSTM]

Hi @cstyx,

Thank you for this report too. please refer to my other comment. The two issues may be related.

With regards,

[cstyx]

Hi @ALABSTM,

as mentioned the content of the FDCAN_RxHeaderTypeDef property data_length as provided by HAL_FDCAN_GetRxMessage() is always 0x0000.

Regards

[KRASTM]

Hello @cstyx,

Could you please share more details, like screenshots of FDCAN_RxHeaderTypeDef when the problem occurs. In my tests with your project, the data_length property consistently shows a value other than 0.

with regards

[cstyx]

Hi @KRASTM

I attached a screen shots of the H723 sender. First is the tx_header and p_can_data as given to function HAL_FDCAN_AddMessageToTxFifoQ(p_hcan, &tx_header, p_can_data) containing 4 Bytes of data as indicated by DLC = 4

th second one is the same message measured on the CAN BUS but the DLC seems to be 0 and data is already missing

[cstyx]

Hi @KRASTM

I think I found the error at FW_H7 V1.11.1 file stm32h7xx_hal_fdcan.c in function static void FDCAN_CopyMessageToRAM(FDCAN_HandleTypeDef *hfdcan, FDCAN_TxHeaderTypeDef *pTxHeader, uint8_t *pTxData, uint32_t BufferIndex)

at code line

for (ByteCounter = 0; ByteCounter < DLCtoBytes[pTxHeader->DataLength >> 16]; ByteCounter += 4U)

For CAN classic and CANFD the DLC for 4 bytes is "4" but this line shifts it 16 bit to the right so it will be always 0. The following for loop won't be entered and no data will be copied at all. Only TxElementW2 still holds the right data length of "4" but that doesn't seem to matter.

[KRASTM]

Hello @cstyx,

I don't understand, at first, you mentioned that you used FW_H7 V1.11.2, and now you suspect an error in FW_H7 V1.11.1!

Since the actual version of the FW_H7 is V1.11.2, and there were some updates related to FDCAN, include that line of code. So, I recommend you, to use the last version.

Thank you for your contribution, please allow me to close this thread.

with regards,