Unable to append data to a file in SD Card.

[Abhishek Deouskar]

Hello,

I am using a F413ZHTx Controller on a custom board. I am logging data onto the SD card using SDIO interface.

Since I am logging a lot of data, I created a code to:

1) Open the file on the SD card

2) Log 100 entries

3) Close the SD card file

4) Reopen the file.

5) Using f_lseek move to the last location and try appending data.

However, this is still resulting in data being overwritten every 100 entries instead on appending.

Here is my source code:

 FRESULT fr;
 uint testbyte;
 
 if(f_mount(&myFATFS, "0:" , 1) == FR_OK)
 {
//	 open_append(&myFILE0, "log.csv");
	 f_open(&myFILE0, "log.csv", FA_WRITE | FA_OPEN_APPEND);
 }
 
 count = preload_count;
 HAL_CAN_ActivateNotification(&hcan1, CAN_IT_RX_FIFO0_MSG_PENDING);
 HAL_CAN_Start(&hcan1);
 CAN_Filter_IDList(ID_00, ID_01, 0, 0, ENABLE);
// CAN_Filter_IDList(ID_02, ID_03, 0, 0, ENABLE);
// CAN_Filter_IDList(ID_04, ID_05, 0, 0, ENABLE);
// CAN_Filter_IDList(ID_06, ID_07, 0, 0, ENABLE);
// CAN_Filter_IDList(ID_08, ID_09, 0, 0, ENABLE);
 
 /* USER CODE END 2 */
 
 /* Infinite loop */
 /* USER CODE BEGIN WHILE */
 while (1)
 {
	if(Received_00)
	{
//		char data1[] = "Inside\n";
//		HAL_UART_Transmit(&huart7, (uint8_t*)data1, sizeof(data1), 500);
		Received_00 = 0;
		count--;
		if(count < preload_count && count > 0)
		{
//			open_append(&myFILE0, "log.csv\0");
			sprintf(CANdata,"0x%X, %d | %d | %d | %d | %d | %d | %d | %d\n", RxMessage.ExtId, RxMessage_Data[0], RxMessage_Data[1], RxMessage_Data[2], RxMessage_Data[3], RxMessage_Data[4], RxMessage_Data[5], RxMessage_Data[6], RxMessage_Data[7]);
			fr = f_write(&myFILE0, CANdata, strlen(CANdata), &testbyte);
			CAN_Filter_IDList(ID_00, ID_01, 0, 0, ENABLE);
			char data2[] = "count\n";
			HAL_UART_Transmit(&huart7, (uint8_t*)data2, sizeof(data2), 500);
		}
		else if(count == 0)
		{
			char data3[] = "100 Written\n";
			HAL_UART_Transmit(&huart7, (uint8_t*)data3, sizeof(data3), 500);
			f_close(&myFILE0);
			CAN_Filter_IDList(ID_00, ID_01, 0, 0, ENABLE);
 
			count = preload_count;
		}
		else if(count == preload_count)
		{
			char data1[] = "Next 100\n";
			HAL_UART_Transmit(&huart7, (uint8_t*)data1, sizeof(data1), 500);
 
			f_open(&myFILE0, "log.csv", FA_WRITE | FA_OPEN_APPEND);
			f_lseek(&myFILE0, f_size(&myFILE0));
//			open_append(&myFILE0, "log.csv");
			CAN_Filter_IDList(ID_00, ID_01, 0, 0, ENABLE);
		}
	}
 
/*****************************************************************************/
/*I also tried using the open_append function I found on ELM_CHAN website, but it didn't work for me.*/
/* USER CODE BEGIN 4 */
FRESULT open_append (
 FIL* fp, /* [OUT] File object to create */
 const char* path /* [IN] File name to be opened */
)
{
 FRESULT fr;
 
 /* Opens an existing file. If not exist, creates a new file. */
 fr = f_open(fp, path, FA_WRITE | FA_OPEN_ALWAYS);
 if (fr == FR_OK) {
 /* Seek to end of the file to append data */
 fr = f_lseek(fp, f_size(fp));
 if (fr != FR_OK)
 f_close(fp);
 }
 return fr;
}
 
/* USER CODE END 4 */

[AvaTar]

Try f_lseek() to set the file pointer to the end before writing.

The OPEN_APPEND flag names a capability, not an automatism.

[Abhishek Deouskar]

Hello AvaTar,

This section of the code does the same thing. After the first preload_count entries are written, then the preload_count is loaded back into the count variable and then I open the file again and perform f_lseek first before writing into the file.

Should I add a f_lseek to the first time I am creating or opening the file?

else if(count == preload_count)
{
	char data1[] = "Next 100\n";
	HAL_UART_Transmit(&huart7, (uint8_t*)data1, sizeof(data1), 500);
 
	f_open(&myFILE0, "log.csv", FA_WRITE | FA_OPEN_APPEND);
	f_lseek(&myFILE0, f_size(&myFILE0));
//	open_append(&myFILE0, "log.csv");
	CAN_Filter_IDList(ID_00, ID_01, 0, 0, ENABLE);
}

[Abhishek Deouskar]

Hello,

I solved the issue. The issue was not of the SDIO interface but my logic for count.

Thanking You.

[AvaTar]

Didn't mess much with FATFS recently, but the usual clib way is calling fseek(..,..,SEEK_END) after opening the file. Your code looks fine, have you tried to debug it ?

I use to stick to simple use cases - like write- only, one file per session, file name created from date/time.

And since I mostly write medium-sized strings at a lower rates, I call f_sync() after each write.

FATFS is a limited replacement for the clib. I use to write persistant data from a MCU application, to evaluate them "offline" on a PC.

[Abhishek Deouskar]

Nice. I did not read up properly on what f_sync does. Now I realize Why I am even closing the file at all when I can simply use the f_sync function.

Thanks @Community member​