From: jim bell <jimbell@pacifier.com>
Date: Thu, 8 Aug 1996 08:42:26 +0800
To: Bill Stewart <stewarts@ix.netcom.com>
Subject: Re: Digital Telephony costs $2
Message-ID: <199608071650.JAA05697@mail.pacifier.com>
MIME-Version: 1.0
Content-Type: text/plain


At 11:00 PM 8/6/96 -0700, Bill Stewart wrote:
>At 11:34 PM 8/5/96 -0800, you wrote:
>>What is unclear, however, is WHY they "had to" build a card that couldn't do 
>>full-duplex.  I mean, would there have been a problem implementing that?  Or 
>>was this just another one of those stupid design decisions which could have 
>>been easily fixed if it had been realized in time?

>2) DSPs tend to be really tight on resources, especially RAM,
>   which you need to do multiple programs at once.  $5-10 DSPs are 
>   especially tight.  They're starting to come with mini operating systems.

I wasn't aware that sound cards made appreciable use of DSP's.  Unlike 
modems, which inherently must massage large amounts of signal to get the 
data, I assumed that sound cards were more like straight A/D/A systems.



>>> It also has the advantage
>>>that the data is being moved through your CPU, so encryption is
>>>an easy add-on, rather than having one combined modem/voiceblaster
>>>card which doesn't have any hooks for crypto or other processing.
>>Well, I assume that if implemented as a new type of modem card, the 
>>processor can be used to do the data transfer.
>
>If you're doing the voice crunching and A/D conversion and telephony
>all on the modem card, with everything tightly integrated
>to fit in your tiny cache, why put in hooks for the processor to intervene?

You'd put in a hook because it would be easily done, and to fail to do so 
would be a serious mistake.  It could also be bypassed by a hardware switch, 
I suppose, or a software-controlled switch, to make processor intervention 
unnecessary.


Jim Bell
jimbell@pacifier.com