Serial read works for only a few seconds

I am reading data packets trough serial port to MATLAB and try to plot it. The data packet has a 2-byte token in the beginning, a 3-byte some other message in the middle and an 8-byte adc data for 2 channels. In the code (got most parts from https://billwaa.wordpress.com/2013/07/10/matlab-real-time-serial-data-logger/ ), I wait for the token and store the rest of the data packet in a buffer.

    while ishandle(plotGraph) %Loop when Plot is Active
       while (not(isequal(fread(s,2),TOKEN))) % tokn is a 2x1 uint8 vector
       end 
       payload(1:11,1) = fread(s,11); % Read USEFUL information (11 bytes) from Serial
       % parse data 
    end

However, the plot and data saving work fine only for the first few seconds and then the data is crashed. I checked the workspace and find that the token was saved into the buffer as useful information for the crashed data. I tried to rerun the program several times and it turns out that it messed up at the same time.

I have attached my code and I appreciate if anyone has any comments to it.

Answer 1

[Walter Roberson]

I notice that you typecast() to int32 . I would worry about about the byte order of the devices is the same.

>> typecast(uint8([1 2 3 4]), 'int32')
ans =
  int32
   67305985
>> dec2hex(ans)
ans =
    '4030201'

That is, your MATLAB side is using "Little-Endian" byte order, where the first byte in memory is the least significant byte. Is it known that the device producing the data is writing in the same order?

[Taoran]

Hi, Walter. Thank you for your response. For now, I think the data parsing should be okay because for the first several seconds the plot is what I expected. My problem is that the "wait for token" part seems not working after first 5 seconds because I found token in my data buffer.