I have not found any documentation neither, but after having played around with the various options to get data in realtime, I've noticed the following:
Getting realtime data with the callback method
I've made somewhat mixed experience with using a callback method, especially in an app, it consumed a lot of resources and the callback is called very irregularely. It also made my application very slow, because it is called multiple times per second, and there does not seem to be any control over the call frequency.
instrument = slrealtime.Instrument('path_to_model.mldatx');
instrument.addSignal(path, 1);
inst.connectCallback(@(o,e)thisisacallback(o,e));
instrument.AxesTimeSpan = 10;
instrument.AxesTimeSpanOverrun = 'wrap';
tg.addInstrument(instrument);
Getting realtime data with getBufferedData
The following code works very well, instrument.getBufferedData() and datas(...) takes only very little time to execute. I prefer this solution as I have control over when data is read out.
instrument = slrealtime.Instrument('path_to_model.mldatx');
instrument.addSignal('path_to_signal', 1);
tg.addInstrument(instrument);
instrument.BufferData = true;
datas = instrument.getBufferedData();
data = datas('path_to_signal:1');
Maybe this helps a bit.
