startBackground (data acquisition toolbox) blocks Matlab for 300-400 ms

Hi,

I'm using startBackground to send a sine wave through one of four output channels. startBackground blocks matlab for about 300-400 ms, but I need to execute the next command directly (max 10 ms delay, preferably less) after the output has been send.

The behavior seems independent of the size of the queued data and the number of output channels. The delay is not constant, but varies around 100 ms across repetitions.

Below is a reproducable example.

Thanks.

%set parameters

stimParams.NIdaqRate = 1000;

stimParams.NIdaqName = 'cDAQ1mod1';

stimParams.noOutputChannels = 4;

stimParams.signalFrequency = 40; %in Hz

stimParams.signalDuration = .05; %in seconds

stimParams.samplesPerPulse = stimParams.signalDuration * stimParams.NIdaqRate;

stimParams.pulse = 1 + sin(linspace(0, ...

(2*pi*stimParams.signalFrequency/stimParams.NIdaqRate * stimParams.samplesPerPulse), ...

stimParams.samplesPerPulse)');

% Initialize session and parameters

NiDaqDevice = daq.createSession('ni');

NiDaqDevice.Rate = stimParams.NIdaqRate;

% Add output channels to the session

for ii = 0:(stimParams.noOutputChannels - 1)

%create name for the channel depending on stimulator number

stimName = sprintf('ao%d', ii);

%add channel

addAnalogOutputChannel(NiDaqDevice, stimParams.NIdaqName, stimName, 'Voltage');

end

%% iterate through repetitions %%

for repetition = 1:10

%randomly select a channel

outPutChannelIdx = randi(4);

%reset current output matrix

currentOutput = zeros(stimParams.noOutputChannels, stimParams.samplesPerPulse);

%add pulse at current output channel to output matrix

currentOutput(outPutChannelIdx,1:length(stimParams.pulse)) = stimParams.pulse;

% Queue the data

queueOutputData(NiDaqDevice, currentOutput');

% make very sure the queuing is not the problem

pause(1);

%start timer

tic;

%start background execution

NiDaqDevice.startBackground;

% stop timer

toc

%pause shortly

pause(1 + rand());

end