Missing documentation for slrealtime.Instrument methods?

Hello,

I'm trying to evaluate a setup for real time testing. I've found useful information on this link, where it is shown how to leverage python scripting to run a slrealtime application and get the acquired signals from the real time HW.

The script runs fine, but in an attempt to extend it for our purposes, I'm struggling to find some documentation on some of the methods used in such script. For example:

instrument.getBufferedData % no doc for getBufferedData method

and:

instrument.BufferData=true % no docs for BufferData property

The purpose is to be able to get signal values in real time in order to take actions during the execution of a test case.

Thanks in advance for any help!

Leonardo

Answer 1

[Pablo Romero]

You can find more information about the getBufferedData method and the BufferData property at Gets data from the real-time application instrument buffer - MATLAB getBufferedData (mathworks.com).

Please notice that the main purpose of the buffered data mode is providing support for external languages via the MATLAB Engine API that do not support callbacks. Using buffered data mode is not strictly required when manipulatin real-time data within MATLAB.

[Hui Xiao]

The example code provided in the officical documentation is very confusing:

mldatxfile = 'slrt_ex_tank.mldatx';
hInst = slrealtime.Instrument(mldatxfile);
connectCallback(hInst,@my_callback);
addSignal(hInst,'slrt_ex_tank/ControlValue',1);
% . . . change from normal (not buffered) data mode 
% . . . change to buffere data mode
Instrument.BufferedData = true;
% . . . inside the my_callback (an slrealtime.instrument callback), 
% . . . you can call getBufferedData
myData = getBufferedData(hInst);

1) the variable Instrument is not decleared anywhere, execute

Instrument.BufferedData = true;

will just create a structure variable. From the answers by Marchel Schoch below, seems that it should be

hInst.BufferedData = true;

2) the example code implied that getBufferedData is called in the callback function. But the description of getBufferedData function is saying that the purpose of it is get ride of callback function.

[Hui Xiao]

slrealtime.Instrument object don't have a public propertiey BufferedData, so I am still confused on how to enable the buffered data mode.

[Stefanie Schwarz]

Hi Hui, there is a typo in the 'getBufferedData' our documentation. It should be:

Instrument.BufferData = true;

('BufferData', not 'BufferedData').

We apologize for this and will fix the typo in the future MATLAB documentation.

Answer 2

[Marcel Schoch]

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));   % adding a callback method
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; % set buffered to true
% read out data:
datas = instrument.getBufferedData();
data = datas('path_to_signal:1');

Maybe this helps a bit.