Missing Serial Port Data

I am currently working on a GUI-based application that records serial data from an embedded system that is transmitted at 50Hz. The problem is that MATLAB appears incapable of recording this data reliably, and drops samples. The format of the transmitted data is as follows:

    4918  22279  29342   3161      0  24953  29814   5319      1      0
    4919  22279  29348   2997      1  24953  29838   5037      0      0
    4920  22279  29357   2682      0  24953  29853   4544      0      0

Each row is terminated by a CR/LF. I have written a test function to try and figure out what is going on - the code for this is below.

    function stack_stream(time)
        column_count = 10;

        serial_object = create_serial_object;
        fopen(serial_object);

        date_vector = clock;
        file_name = datestr(date_vector,30);
        file_name = [file_name '.txt'];

        file_identifier = fopen(file_name,'w');
        tic;

        while (toc < time)
            if (serial_object.UserData.is_new_data == true)
                raw_chunk = serial_object.UserData.data;
                serial_object.UserData.is_new_data = false;

                data_chunk = sscanf(raw_chunk,'%d');
                data_chunk_length = length(data_chunk);

                if (mod(data_chunk_length,column_count) == 0)
                    data_column_count = data_chunk_length/column_count;

                    data = reshape(data_chunk,column_count,data_column_count);

                    fprintf(file_identifier,...
                        '%6d %6d %6d %6d %6d %6d %6d %6d %6d %6d\r\n',data);
                end
            end
        end

        fclose(file_identifier);
        fclose(serial_object);
        delete(serial_object);
    end

    function serial_object_callback(object,event)
        new_data = fscanf(object,'%c',object.BytesAvailable);

        if (object.UserData.is_new_data == false)
            object.UserData.data = new_data;
            object.UserData.is_new_data = true;
        else
            object.UserData.data = [object.UserData.data new_data];
        end
    end

    function serial_object = create_serial_object()
        serial_object = serial('COM2');

        serial_object.BaudRate = 57600;
        serial_object.DataBits = 8;
        serial_object.FlowControl = 'none';
        serial_object.StopBits = 1;

        serial_object.Terminator = 'CR/LF';
        serial_object.InputBufferSize = 2^18;
        serial_object.BytesAvailableFcnMode = 'terminator';
        serial_object.BytesAvailableFcn = {@serial_object_callback};

        serial_object.UserData.data = [];
        serial_object.UserData.is_new_data = false;
        serial_object.UserData.response = [];
        serial_object.UserData.is_new_response = false;
    end

In essence, this function writes `time` seconds worth of data to file, using a callback to transfer data between the serial object buffer and a user buffer. Using `stack_stream` I find that I miss around 10 rows of data for every 3000 received - ie about 10 a minute.

Anecdotal evidence would lead me to believe that MATLAB is capable of handling serial data in the kHz range, so I am at somewhat of a loss to determine why I cannot get it to work properly at a paltry 50Hz. Is there anything I can do to improve performance without having to resort to the real-time target for windows or the like?

[Varsha Parthasarathy]

Hey Rodney! Were you able to fix your problem? I am having similar issues where I always miss about 10% of my samples during serial communications.

Thanks

Answer 1

[Walter Roberson]

Never use 57600 baud without hardware flow control.

[Rodney]

Given that I can use Hyperterminal to record the data stream, and not miss a single line of data in several hours of acquisition, the problem is not the lack of hardware flow control. Its MATLAB.