Received FDCAN 64bytes data but FDCAN_RxHeader.datalength is 15, is it a bug?

[dqsh06]

Split from this thread.

thanks to @Ozone @Karl Yamashita,

this afternoon I have tried to extend can2.0 to canfd with my project of stm32g474vet6.  I found some strange things, I think there may be a bug of stm32g474vet6 fdcan module.

I modifed the FDCAN_TxHeader to FD_Frame and datelength to 64byte. for  FDCAN_RxHeader, almost nothing to modify. then i used an app on PC to send a 64bytes CAN message,  then my code received the 64bytes message and copied to rxbuffer, the rxbuffer had 64bytes data, but FDCAN_RxHeader.datalength is 15. it is not 64. 

i think this is a bug of stm32g474vet6, it received 64bytes data but FDCAN_RxHeader.datalength is 15. I have no can tool now (with used by other people), when i have the can tool, i will take screenshot to show the strange thing.

hello @mƎALLEm @Saket_Om did you meet FDCAN received 64bytes but  FDCAN_RxHeader.datalength is 15? is there some configuration I miss?

Thanks a lot!

[mƎALLEm · Accepted solution]

---

@dqsh06 wrote:

hello @mƎALLEm @Saket_Om did you meet FDCAN received 64bytes but  FDCAN_RxHeader.datalength is 15? is there some configuration I miss?

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This is not a bug and the information is provided in the reference manual RM0440 Rev 9:

DLC=15 means 64 bytes!

[Karl Yamashita]

When using ST's data structure for FDCAN_RxHeaderTypeDef, you should look what the reference is for DataLength, which they reference FDCAN_data_length_code 

/**
  * @brief  FDCAN Rx header structure definition
  */
typedef struct
{
  uint32_t Identifier;            /*!< Specifies the identifier.
                                       This parameter must be a number between:
                                        - 0 and 0x7FF, if IdType is FDCAN_STANDARD_ID
                                        - 0 and 0x1FFFFFFF, if IdType is FDCAN_EXTENDED_ID               */

  uint32_t IdType;                /*!< Specifies the identifier type of the received message.
                                       This parameter can be a value of @ref FDCAN_id_type               */

  uint32_t RxFrameType;           /*!< Specifies the the received message frame type.
                                       This parameter can be a value of @ref FDCAN_frame_type            */

  uint32_t DataLength;            /*!< Specifies the received frame length.
                                        This parameter can be a value of @ref FDCAN_data_length_code     */

  uint32_t ErrorStateIndicator;   /*!< Specifies the error state indicator.
                                       This parameter can be a value of @ref FDCAN_error_state_indicator */

  uint32_t BitRateSwitch;         /*!< Specifies whether the Rx frame is received with or without bit
                                       rate switching.
                                       This parameter can be a value of @ref FDCAN_bit_rate_switching    */

  uint32_t FDFormat;              /*!< Specifies whether the Rx frame is received in classic or FD
                                       format.
                                       This parameter can be a value of @ref FDCAN_format                */

  uint32_t RxTimestamp;           /*!< Specifies the timestamp counter value captured on start of frame
                                       reception.
                                       This parameter must be a number between 0 and 0xFFFF              */

  uint32_t FilterIndex;           /*!< Specifies the index of matching Rx acceptance filter element.
                                       This parameter must be a number between:
                                        - 0 and (SRAMCAN_FLS_NBR-1), if IdType is FDCAN_STANDARD_ID
                                        - 0 and (SRAMCAN_FLE_NBR-1), if IdType is FDCAN_EXTENDED_ID */

  uint32_t IsFilterMatchingFrame; /*!< Specifies whether the accepted frame did not match any Rx filter.
                                         Acceptance of non-matching frames may be enabled via
                                         HAL_FDCAN_ConfigGlobalFilter().
                                         This parameter can be 0 or 1                                    */

} FDCAN_RxHeaderTypeDef;

You can see how they defined the values

/** @defgroup FDCAN_data_length_code FDCAN Data Length Code
  * @{
  */
#define FDCAN_DLC_BYTES_0  ((uint32_t)0x00000000U) /*!< 0 bytes data field  */
#define FDCAN_DLC_BYTES_1  ((uint32_t)0x00010000U) /*!< 1 bytes data field  */
#define FDCAN_DLC_BYTES_2  ((uint32_t)0x00020000U) /*!< 2 bytes data field  */
#define FDCAN_DLC_BYTES_3  ((uint32_t)0x00030000U) /*!< 3 bytes data field  */
#define FDCAN_DLC_BYTES_4  ((uint32_t)0x00040000U) /*!< 4 bytes data field  */
#define FDCAN_DLC_BYTES_5  ((uint32_t)0x00050000U) /*!< 5 bytes data field  */
#define FDCAN_DLC_BYTES_6  ((uint32_t)0x00060000U) /*!< 6 bytes data field  */
#define FDCAN_DLC_BYTES_7  ((uint32_t)0x00070000U) /*!< 7 bytes data field  */
#define FDCAN_DLC_BYTES_8  ((uint32_t)0x00080000U) /*!< 8 bytes data field  */
#define FDCAN_DLC_BYTES_12 ((uint32_t)0x00090000U) /*!< 12 bytes data field */
#define FDCAN_DLC_BYTES_16 ((uint32_t)0x000A0000U) /*!< 16 bytes data field */
#define FDCAN_DLC_BYTES_20 ((uint32_t)0x000B0000U) /*!< 20 bytes data field */
#define FDCAN_DLC_BYTES_24 ((uint32_t)0x000C0000U) /*!< 24 bytes data field */
#define FDCAN_DLC_BYTES_32 ((uint32_t)0x000D0000U) /*!< 32 bytes data field */
#define FDCAN_DLC_BYTES_48 ((uint32_t)0x000E0000U) /*!< 48 bytes data field */
#define FDCAN_DLC_BYTES_64 ((uint32_t)0x000F0000U) /*!< 64 bytes data field */