Analog Outputs stops (without reason) ?!
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I hope one of you can help me!
I am working on a Programm using DAQ-Toolbox and a National Instruments I/O USB Card. I am trying to output data continuously by using an analog outputobject. It got a Samplerate of 100 and 100 Values get enqueued before the object is started. After start a timerfunction enqueues new Data by using "putdata". The first 100 Samples are output fine but than the object stops though there are still 400 Values in the queue. It stops without any error message.
Why does the object stop?
In my opinion the object should run until no more data is left in the queue... .
If you need further information for an answer just let me know!
Walter Roberson on 14 Dec 2011
Usually USB buffers data until the USB packet size (close to 1000 bytes) is met. If your data is 2 bytes per sample, your buffer is getting drained until less than ~1000 bytes is left.
USB is not suitable for continual output of short packets -- at least not without getting in to details of USB that Mathworks has never exposed the user to.
Can you post bit of the code? Also are you using the new Session based interface (R2011b) or the legacy interface ?
Session Based Interface http://www.mathworks.com/help/toolbox/daq/bsob84e-1.html#bsovlz7-1
If you are using the legacy interface (analogoutput object) then you might need to set this property:
Looking at the documentation, it states that all the data must be queued using putdata before starting the analogoutput object.
So the TimerFcn will not work, unless you do the following: a) Change the TriggerType to Manual, b) and retrigger after putting more data.
A more convenient solution would be offered by Session based architecture which is perfect for this:
I am assuming you are doing both input and output simultaneoulsy! You can use Background operations to continuously queue data to to be output (using a DataRequired callback), example: http://www.mathworks.com/help/toolbox/daq/bsob84e-1.html#bsovlz7-1
You can also do both Input and Output simultaneously and do a live plot using 'DataAvailable' for inputs! http://www.mathworks.com/help/toolbox/daq/bsotkz_-1.html (You might want to use startBackground(), if you want the output data to happen in the background)