Sending a complete file at once from SD card to Mobile App using NRF52840.

[Samiulhaq]

Hello Nordic Family. I hope this post finds you well. 

I am working on a project where I have connected multiple sensors to the NRF52840. I have collected all the sensor's data and saved it on the SD card as a CSV file. The file size is about 240MB which has 60 Hours of data from all the sensors(client requirements). Now I want to send this complete file at once from the SD card to the Mobile App in the fastest possible way. I have run the below program on my board

/cfs-file/__key/communityserver-discussions-components-files/4/8204.ble_5F00_app_5F00_uart_5F00_fatfs_5F00_send_5F00_sdk_5F00_16.0.0.zip.

but this program reads data one by one byte from the SD card and sends it byte by byte to the mobile app which I don't want. I want to send the whole file at once in the fastest possible way not byte by byte. Any help regarding this will be highly appreciated. 

Best Regards,

Sami 

[Samiulhaq]

Thank you Hakan, for the thorough explanation. 

It concluded that the problem is with the mobile app side(central ) not the peripheral, am I right? 

One last question and sorry for taking your precious time. I want to read a large file (about 240MB) from the SD card but the problem is that when I increase the #define FILE_SIZE_MAX (Maximum size in bytes of the file to be read from SDCARD) greater than 220000, while the following;

                static uint8_t file_buffer[FILE_SIZE_MAX]; 

              ff_result = f_read(&file, file_buffer, FILE_SIZE_MAX, (UINT *) &bytes_read);

 Then it gives the following error:

              .bss is too large to fit in RAM1 memory segment
              .heap is too large to fit in RAM1 memory segment
               section .heap overlaps absolute placed section .stack
               section .stack VMA [000000002003e000,000000002003ffff] overlaps section .bss VMA 

                 [0000000020002c64,0000000020224b08]         

I don't know how to solve this. Simply I want to read the whole file (234MB) from the SD card at once and then send it in chunks to the mobile app, Is this possible or do I have to read in chunks from the SD card too? 

Kind Regards,

Sami 

[Håkon Alseth]

Hi Sami,

Samiulhaq said:

It concluded that the problem is with the mobile app side(central ) not the peripheral, am I right? 

Yes, it is the central that drives the communication and essentially sets all the rules. A peripheral can ask for certain parameters, but it is the central that eventually grants permissions.

Samiulhaq said:

I don't know how to solve this. Simply I want to read the whole file (234MB) from the SD card at once and then send it in chunks to the mobile app, Is this possible or do I have to read in chunks from the SD card too? 

You are running out of RAM by trying to buffer ~220kB of data. You must handle this in a smaller buffer.

 

Kind regards,

Håkon

[Samiulhaq]

Thanks Hakan for helping.

Håkon Alseth said:

Yes, it is the central that drives the communication and essentially sets all the rules. A peripheral can ask for certain parameters, but it is the central that eventually grants permissions.

Okay Sir, I understand, and thank you for the thorough explanation. 

Håkon Alseth said:

You are running out of RAM by trying to buffer ~220kB of data. You must handle this in a smaller buffer.

Can you please refer me to a thread/blog where they have accessed and read large data from SD in small chunks/buffer? I have tried but I am unable to read the large file in a small buffer. I will be very thankful to you. 

Best Regards,

Sami

[Håkon Alseth]

Hi,

 

Samiulhaq said:

Can you please refer me to a thread/blog where they have accessed and read large data from SD in small chunks/buffer? I have tried but I am unable to read the large file in a small buffer. I will be very thankful to you. 

I do not think we have a blog/thread for this scenario.

What you need to handle is a arbitrary byte stream going into a buffer, which again is passed through your bluetooth link. You should not need to buffer many kilobytes of data from the SD card, you need to read SD-data out into your buffer and pass the data through the bluetooth link.

 

Kind regards,

Håkon

[Samiulhaq]

Hi Hakan, thanks for the suggestion.

Yes exactly I have done the same and now I am able to read data from the SD card and send it to the mobile app continuously.  Below code snippet is my approach;

#define FILE_SIZE_MAX                   BLE_NUS_MAX_DATA_LEN  // file size is same as the packet size
static uint8_t file_buffer[FILE_SIZE_MAX];
ff_result = f_open(&file, FILE_NAME, FA_READ);

for (;;)
    {
        if(file_send_to_peripheral)
        {

           file_actual_read_size = (f_size(&file));
           uint32_t remaining_bytes = file_actual_read_size;  
           uint16_t chunk_length = BLE_NUS_MAX_DATA_LEN;
           ret_code_t err_code;

            if(file_actual_read_size > 0)
            {

            while(remaining_bytes > 0)
             {

             ff_result = f_read(&file, file_buffer, sizeof(file_buffer), (UINT *) &bytes_read);
             err_code= ble_nus_data_send(&m_nus, file_buffer, &chunk_length, m_conn_handle);

                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;
        }
        idle_state_handle();
    }
}

Is this the efficient way of reading from the SD card and sending it to the Mobile App?

Best Regards,

Sami