nrf52840 usb msc qspi slow writing speed and losing frames

[yanglin lian]

Hi, I have recently acquire an nrf52840 development board to prototype a usbd msc. With the example provided in sdk17.02-USBD_MSC, for saving every 1000 frames of data, 100 frames of data are lost.

The flash chip is mx25r6435.

// here saving_num = 1000.

if((saving_count < saving_num)&& writing_flag)
{

   char temp_value[100];
   sprintf(temp_value,"%d",time_count);
   memcpy(temp_value + strlen(temp_value),ENDLINE_STRING,sizeof(ENDLINE_STRING));
   NRF_LOG_INFO("%s",temp_value)
   ff_result = f_write(&file, temp_value, strlen(temp_value) - 1, (UINT *) &bytes_written);
   if (ff_result == FR_OK)
   {
       NRF_LOG_INFO("%d bytes written.", bytes_written);
    }
   else
   { 
       NRF_LOG_INFO("writing failed");
    }
   writing_flag = false;
   saving_count = saving_count +1;
    }
   if (saving_count == saving_num)
   {
       saving_count = saving_count +1;
       ff_result = f_sync(&file);
       if (ff_result == FR_OK)
       { 
          NRF_LOG_INFO("sync success.");
       }
  }

[yanglin lian]

if I set the first timer interrupt to 100ms. Most of the time the saving duration is 0, but sometimes is 108. All of these projects are running with NRF52840 DK.