RE: OpenG VISA

[Rolf K. <rol...@ci...>]

Hi Jean-Pierre,

> Rolf, what is this visa32.dll? It seems to be a NI product so=20
> I don't think you meant OpenG VISA to be a replacement of NI-VISA.

Well, the VXI PnP Alliance has made a standard available in the form
of VISA. And yes in sense if you want to do your own VISA you will
have to replace VISA32.DLL. This is the common API to all VISA services
and this DLL then will distribute the commands to the according lower
level driver according to the VISA resource identifier.

It is unfortunate that VISA32.DLL has to be replaced entirely but that
is the way it was designed. I'm not entirely sure how HP does it but I
feel that if you install HP hardware for instance you seem to have some
sort of problem in that you need to decide if you want to have NI-VISA
and only use a limited set of HP hardware supported by it or install
HP VISA and only have limited support for standard NI hardware.

The interface between VISA32.DLL and the low level drivers is nowhere
documented that I could find it and although I have a fairly good
general idea how it is done, trying to figure out all the nitty gritty
details is really a big nono, so the most straightforward method is
indeed replacing VISA32.DLL altogether to get rid of any possible NI
licensing issues.

This however has some implications. In that way you won't have support
for any interface unless there is an approapriate OpenG (or whatever)
low level VISA driver avaialable. While I started with the ASRL driver
already (but it is by no means near a working state yet) I have no
idea how complicated the addition of drivers for GPIB, TCP/IP, USB etc
might be. GPIB seems fairly straightforward to me but I haven't really
looked into that yet.

> would like to have a serial interface to get rid of VISA=20
> installation when I want to use the serial port on target=20
> computers. Both licensing fees and installation footprint
> make no sense for me for the mere use of the serial port.

I would estimate the base driver to be around 100k for the VISA32.DLL
and at most 100k for each low level driver. There probably would have
to be a small UI application for configuration tasks too, although
that could be handled through ini files entirely for starters.=20

> Like VISA, I 'd like to see a generic communication API where=20
> the interface would be the same whatever the actual communication
> channel is (serial, TCP, etc). It would be OOP so when there=20
> is a need for another communication channel, just provide a specific
> implementation that is simply integrated. How difficult would=20
> it be to build an interface to Windows (or your favorite OS) serial
> drivers? Gateways (like serial<->TCP to access serial port on=20
> remote computers) to connect any two different channels could also be
> implemented.

Well it is C programming and support in that area is very limited in
the LabVIEW community. I have had no positive feedback until now and
can't possibly take on this task alone. For this reasons I postboned
further work for the time being.

Rolf Kalbermatter
CIT Engineering Nederland BV    tel: +31 (070) 415 9190
Treubstraat 7H                  fax: +31 (070) 415 9191
2288 EG Rijswijk	http://www.citengineering.com
Netherlands		mailto:rol...@ci...
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