Writing large ammount of data over serial is very slow

Hi!

I'm trying to send around 960 000+ uint8 samples to an arduino due using serial ports (not using the toolbox for arduino since there is many arduinos connected at the same time). This takes about 40s with a baudrate of 250 000, having to send this 64 times it would take a little more than 40 minutes.

The samples are sent in chunks since the memory in the arduino cannot handle larger data, preferrably it would be in chunks of 64000. The data is sent and then we wait for the arduino to send a char saying that it has read that what was sent. Waiting for ack does not take much time at all (around 0.007s per run) but sending the data with frwite takes about 8s for 200000 samples.

I have tried to change the size of data to be sent, not having the fwrite in the for loop but writing them after eachother. Also taking out the central fwrite call in the fwrite function.

Does anyone have any idea on how to solve this?

THe code is as follows:

    %%------ Send Samples ------ %

    block_size = 200000;
    number_of_blocks = 5;

    [x , fs] = audioread('48kHzSampleSong.wav');
    % Only mono
    x = x(:,1);

    res = 8; % bits per sample
    delta = 0.02; % quantization step size
    [xhat, yhat] = UniformQuantizer(x,2^res,delta);

    % Modify for PWM (y in the interval [0,2^res -1])
    y_hat = yhat+2^(res-1);

    % Convert to bytes for sending
    y_8bit = uint8(y_hat);

    [com] = serialsetup('COM8',250000);
     disp('>> Communication initialized');

    % Choose matlab mode
    fprintf(com,'%c','m'); 

    % Send command to Arduino
    fprintf(com,'%c','s');

    for t=1:number_of_blocks
       idx1 = (t-1)*block_size+1;
       idx2 = idx1+block_size-1;
       tic;
       fwrite(com,y_8bit(idx1:idx2), 'uint8');
       disp1 = toc;

       %fwrite(com,'test', 'uint8', 'async');
         tic;
         wait4Ack(com,'s');
         disp2 = toc;
         disp(strcat('ack ',num2str(t), ' fwrite: ', num2str(disp1), ' w4a: ', num2str(disp2)));
      end

And setup serial:

    % ---- Serial Setup -----
        function [s] = serialsetup(comPort,baudRate)
          %creates serial connection on comPort and sets standard values for the setup
          if(nargin < 2)
            baudRate = 250000;        
          end
          s = serial(comPort);
          set(s, 'DataBits', 8);
          set(s, 'StopBits', 1);  
          set(s, 'BaudRate', baudRate);
          set(s, 'Parity', 'none');
          set(s, 'Timeout', 20);

    %change output/input buffer to be able to send e.g. 1000 bytes a time to slaves. 
          %Default is 512 byte.
          s.OutputBufferSize = 200000;
          s.InputBufferSize = 1024;

Answer 1

[Christoph F.]

A baud rate of 250000/s means a transfer rate of roughly 21000 bytes/s. This means sending 960000 bytes will take about 46 seconds and sending 200000 bytes will take about 9.5s.

> Does anyone have any idea on how to solve this?

Either use a transfer method with a higher bandwidth, or find some way to reduce the amount of raw data that has to be transferred, e.g. by using some form of compression.

[Emma]

Thanks for your answer! I will look at possible ways to reduce the raw data!