MATLAB: How to reduce delay of QueueOutputData() during session

data acquisitionqueueoutputdata()

I am trying to queue some output data during a session. I am using s.startBackround() to collect data in real time and an event listener to queue some output data if a certain condition is met. The delay between when the queueOutputData() is called and the actual time when it outputs the data is about 40ms. I am trying to reduce this delay as much as possible. How can I do this? Is there a way to queue the output data before the function handle, and if it is in the function handle, immediately output this data?
Below is my code:
% initialize session
s = daq.createSession('ni');
% analog inputs
addAnalogInputChannel(s,'Dev1', 'ai1', 'Voltage');
addAnalogInputChannel(s,'Dev1', 'ai2', 'Voltage');
addAnalogInputChannel(s,'Dev1', 'ai3', 'Voltage');
% analog outputs
addAnalogOutputChannel(s,'Dev1', 'ao0', 'Voltage');
s.Rate = 80000;
% not sure how to not start background session without this
data0 = zeros(1,40001)';
data0(end) = [];
queueOutputData(s,repmat(data0, 5, 1));
s.IsContinuous = true;
% event listener where output data can be queued
lh = addlistener(s,'DataAvailable', @kick);
s.startBackground();
s.wait(1000);
stop(s);
handle function:
function kick(src, event)
          % collects all data in single file
          fp = fopen('DATA.bin', 'a');
          X = event.Data;
          T = event.TimeStamps;
          fwrite(fp, [T, X]', 'double');
      if (X(end,1) > 0 && X(end,1)<2.5)
              % row of zeros to determine when queueOutputData() was called
              fwrite(fp,[0 0 0 0]','double');
              % create and queue output data
              outputSingleValue1 = 9;
              outputSignal = [outputSingleValue1*[0:0.01:1 1:-0.01:0] zeros(1,38000)];
              outputSignal(end) = [];
              queueOutputData(src,outputSignal');
      end
          fclose(fp);
   end

Best Answer

To improve performance, do not fopen in a loop: fopen before you designate the callback, and pass the fid to the callback. Also, since your output signal is constant, pre-compute it.
outputSingleValue1 = 9;
outputSignal = [outputSingleValue1*[0:0.01:1 1:-0.01:0] zeros(1,38000)] .';
outputSignal(end) = [];
fp = fopen('DATA.bin', 'a');
lh = addlistener(s,'DataAvailable', @(src,event) kick(src, event, fp, outputSignal));
function kick(src, event, fp, outputSignal)
  % collects all data in single file
    X = event.Data;
    T = event.TimeStamps;
    fwrite(fp, [T, X]', 'double');
    if (X(end,1) > 0 && X(end,1)<2.5)
      % row of zeros to determine when queueOutputData() was called
      fwrite(fp, [0 0 0 0]', 'double');
      % queue the pre-built output data
      queueOutputData(src,outputSignal);
    end
  end
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