Re: Data acquisition in Octave

[Olaf Till]

On Wed, Nov 19, 2008 at 12:04:21PM +0200, Dotan Cohen wrote:
> Can Octave perform DAQ (data acquisition) directly from National
> Instruments DAQ cards, as does MatLAB Simulink?
> 

Data aquisition on Linux is mostly done (and should be done) with the
so called Comedi drivers and the Comedi library. They have good
support for National Instruments cards.

AFAIK there is no general interface of Octave to Comedi as
yet. However, since dynamically linked functions (in Oct-files) can be
generated, you can integrate self-made C-code, which accesses the
Comedi library, into such files and use them from Octave.

Writing such C-code for Comedi is in fact not much more tedious than
using Matlabs DAQ toolbox (I have done both) --- the amount of
learning to use Comedilib is surely not much higher than that for
using all features of the DAQ toolbox (and you need quite a few
features for serious work). An exception is that you need to use some
general Unix functions, e.g. 'select', if you work with Comedilib;
that is where the effort is greater than with the DAQ toolbox. That is
also where some general functions for use with Comedi would probably
be worth making ... OTOH, I ran into a couple of bugs when I tried to
achieve the equivalent functionality with Matlabs toolbox (with an
adapter for 'Data Translation').

I have a C function specialized on simultaneous AI and AO (possibly on
multiple boards) with Comedilib, which can be used from an
Oct-file. It has to get passed a C structure with configuration
information, and pointers to callback-functions to produce/accept
data. It is probably not general enough to be offered to Octave ...

Olaf