online analysis on background data, ni card analog input

Hi,

I am trying to get access to a global variable that is updated in the listener function of a ''DataAvialable'' event, relating to the startbackground for NI card analog input.

It seems that neigther a global variable nor the "UserData" of the daq session object are not updated before stoping the background recording. Is there any way around this to get online access to a variable that is updated in the listener function while the recording is still running?

Thanks,

Ehsan

Answer 1

[Kenny Shu]

When the session's "UserData" variable is updated in the "DataAvailable" event callback, the result is immediately accessible from the workspace.

By setting up the listener as follows,

s1 = daq.createSession('ni');
s1.addAnalogOutputChannel('Dev1','ao1', 'Voltage');


s2 = daq.createSession('ni');
ch = s2.addAnalogInputChannel('Dev1','ai1', 'Voltage');
ch.TerminalConfig = 'SingleEnded';
s2.DurationInSeconds = 60;

lh = addlistener(s2, 'DataAvailable', @dataAvailableCallback);

s1.queueOutputData(linspace(0,10,30000)');
startBackground(s1)
startBackground(s2)

function dataAvailableCallback(src, event) 
src.UserData = [src.UserData; event.Data];
end

you may access the live "UserData" while the acquisition continues in the background:

>> s2.UserData(end)

ans =

    9.1314

[Ehsan]

this doesn't work in the continuous mode.

s2.IsContinunous = true;