How can I read data from a buffer at certain intervals (ie. every 20 ms)?

Question

David 2013-7-17

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/82282-how-can-i-read-data-from-a-buffer-at-certain-intervals-ie-every-20-ms

Hi, I am trying to read data from a buffer every 20 ms. I would like the data to continue to fill up the buffer while I fread it at 20 ms intervals. I used the asynchrnous command for this. However, I am not getting the correct time for data being read from the buffer. I used timerPeriod equal to .02 and had a callback function to an fread. However, the data is not being read at 20ms. (I used tic toc to try to measure times) My reason for doing all this is to plot visually data that is being logged such that the plot updates itself every 20ms.

Attached is my code.

function [x,meas,Bytes,lengthRead]=myfunc()

DATA_LOG_TIME_SEC = 1; s = serial(COM_PORT); s.InputBufferSize = 1000000; s.BaudRate = BAUD_RATE; s.StopBits = 2; s.Timeout = 1.0;

s.Timeout = DATA_LOG_TIME_SEC; s.ReadAsyncMode = 'continuous' ; s.TimerPeriod = .02 ; s.TimerFcn = {'servicetimer'};

tic fopen(s); toc fprintf('INFO: Begin logging data...\n')

fclose(s) ; delete(s) ; end

function y = servicetimer(obj, event)

    global x; 
    global i;
    global meas;
    global Bytes;
    global lengthRead;
    global EmptyCount
    global nonEmptyCount
    while(i<=10)     
   Bytes(i)= obj.BytesAvailable;
   tic;
   meas{i}= fread(obj);
   x(i)=toc;
   lengthRead(i) = length(meas);
   i=i+1;
  end
end