File transfer with cmd code via BLE.

Question

Hi All, 
 I am using NRF52840 with USB MSC code. I have managed to create a file inside flash chip. I am also able to transfer this file via BLE to the app. Now while doing file transfer I am diving the file into 200bytes of chunks and then transmitting data. I am successfully able to transmit the file as well. I have to add a cmd code "0x44" in each 200 byte transfer. How can I do that? 
 File transfer start 
 0x44 + 200 bytes 
 0x44 +200 bytes 
 0x44 + 200 bytes 
 ... 
 end of transfer. 
 Can anyone help me modfiy the code below:- 
 

void read_from_file(void)
{
 FRESULT ff_result;
 FIL file;
 uint32_t bytes_read;


 fatfs_ls();
 
 if(file_found_on_sdcard)
 {
 NRF_LOG_INFO("Reading from file %s",my_filename);
 ff_result = f_open(&file, my_filename, FA_READ);
 if (ff_result != FR_OK)
 {
 NRF_LOG_INFO("Unable to open or create file:%s",my_filename);
 return;
 }

 ff_result = f_read(&file, file_buffer, FILE_SIZE_MAX, (UINT *) &bytes_read);
 if (ff_result != FR_OK)
 {
 NRF_LOG_INFO("Read failed
.");
 }
 else
 {
 NRF_LOG_INFO("%d bytes read.", bytes_read);
 file_actual_read_size = bytes_read;
 }

 (void) f_close(&file);
 }
 else
 {
 NRF_LOG_INFO("No file named %s found",my_filename);
 file_send_to_peripheral = false;
 }
 return;
}


void send_file_to_app(void)
{
 read_from_file();
 
 
 if(file_actual_read_size > 0)
 {
 uint16_t remaining_bytes = file_actual_read_size;
 uint16_t chunk_length = MAX_HRM_LEN;
 ret_code_t err_code;
 while(remaining_bytes > 0)
 {
 //err_code = ble_nus_data_send(&m_nus, &file_buffer[file_actual_read_size - remaining_bytes], &chunk_length, m_conn_handle);
 err_code = rcbr_service_send_data(&file_buffer[file_actual_read_size - remaining_bytes], chunk_length);
 if(err_code != NRF_ERROR_RESOURCES)
 {
 APP_ERROR_CHECK(err_code);
 remaining_bytes -= chunk_length;
 if(remaining_bytes < chunk_length)
 {
 chunk_length = remaining_bytes;
 }
 NRF_LOG_INFO("Remaining bytes to send: %d", remaining_bytes);
 }
 }

 }
 file_send_to_peripheral = false;

}

Thanks & Regards, 
 Snehal

Naeem Maroof · Accepted Answer

Hi Snehal, Thank you for contacting DevZone at NordicSemi. As in the send_file_to_app() function, first you are calling read_from_file() function, which checks if the file is on the sdcard and then opens and reads the file. The function also writes the contents to the file_buffer and number of bytes into file_actual_read_size variable (you might have declared globally). As you want to send the command-character + the data of size chunk_length from the file_buffer There could be different ways to do this, but I think you must construct a new (temporary) buffer of size chunk_length+1 and put 0x44 at location 0 and then copy the data from file buffer and send. I show a cope snippet below, on as is basis, that is exactly doing the same: In this example, I have 10 byte data, and I want to send in chunk-size of 4 I am constructing a new buffer of size 5 and fill it with command and then data int main() { int file_actual_read_size = 10; //number of bytes 10 char file_buffer[10] ={'A','B','C','D','E','F','G','H','I','J'}; //buffer of 10 size int chunksize=4; //transfer size=4 char temp_buffer[5]; //temp buffer of size chunksize+1 int remaining_bytes = file_actual_read_size; //initially all bytes are remaining if(file_actual_read_size > 0) { int itr = 0; while(remaining_bytes > 0) { //fill temp buffer temp_buffer[0] = 0x44; int sindex = file_actual_read_size - remaining_bytes; for(int i=0; i

File transfer with cmd code via BLE.

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