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Date:      Tue, 01 May 2001 17:09:25 -0400
From:      Jason Andresen <jandrese@mitre.org>
To:        Orion Hodson <hodson@aciri.org>
Cc:        freebsd-multimedia@freebsd.org, George Uhl <uhl@rattler-f.gsfc.nasa.gov>
Subject:   Re: " Fwd: RAT problems with aureal vortex1 soundcard "
Message-ID:  <3AEF2605.10F764DB@mitre.org>
References:  <3AEEF94F.7594CEF3@mitre.org> <200105011827.f41IRHe32143@mule.aciri.org>

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Orion Hodson wrote:
> 
> Jason Andresen writes:
> > I don't think any modern version of VAT support half-duplex
> > communication.  Apparently the designers thought that everybody would be
> > using full duplex sound cards by now.  Fortunatly VAT will completely
> > refuse to start if you have a half duplex card or driver.
> 
> Jason
> 
> I think you are confusing RAT and VAT.  RAT only works with full
> duplex cards - I made that (erroneous) design decision when RAT-4 work
> started.  AFAIK VAT has always supported half-duplex cards
> and half-duplex operation with full duplex cards.  Work on VAT stopped
> around 95-96, so there are no "modern" versions, only maintenance has
> gone on since then.
> 
> There was a problem with the freebsd-ports version of VAT misdetecting
> full duplex cards as half-duplex, but it still worked
> (http://www.FreeBSD.org/cgi/query-pr.cgi?pr=23618).  I shall re-check
> the freebsd ports version tonight to be sure unless.

I seem to remember looking at the code for VAT once and discovering that
the half duplex audio was handled by function called
HDsomethingortheother.  That function consisted of one line IIRC:
return 0;

At work, I was supposed to get some SB16s working in full duplex with
4.0.  Unfortunatly I found out later that full duplex was completely
broken in 4.0 and the code we were using was 4.0-kernel specific.  :(

There might be some systems where the half duplex is working (VAT has
several different sound systems that can be selected at compile time)
but the voxware-linux system wasn't one of them.


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