Apparently-To: john.smith@gravis.com


GUS Programmer's Digest     Sat, 29 Jan 94  4:12         Volume 8: Issue  24  

Today's Topics:
        Reading voice while playing it - strange side effects

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	- Meta-info about the GUS can be found at the end of the Digest.
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Date: Fri, 28 Jan 1994 09:47:05 -0500
From: davidm@marcam.com (David MacMahon)
Subject: Re: Reading voice while playing it - strange side effects

>Date: Fri, 28 Jan 1994 10:05:14 SAT
>From: "Michael Patricios" <PATRICIO@odie.ee.wits.ac.za>
>Subject: Reading voice while playing it - strange side effects
>
>I have recently been writing a bit of a MOD player for the GUS and am
>trying to put some oscilloscope type thingys, one for each channel.
>The way I am doing this is to read the voice accumulator position and
>then peek that address in GUS RAM. Works great, the only problem being
>that when I draw the waveforms on the screen, I occassionally get
>weird noises (kinda like "squeaks") coming from my GUS.
>
>If I continuously read the voice position and peek the address, this 
>does not seem to happen, only if I am using graphics at the same time.
>If I just draw a whole lot of crap on the screen without reading 
>anything from the GUS, it doen't seem to happen either. It only seems 
>to happen when I read AND use graphics!!!!!!!
>
>Any ideas anybody??

Does the squeaking happen if you only read the voice position and draw on 
the screen (no peeking)?  Does the squeaking happen when you only peek and 
draw (no reading of voice position)?  Does the squeaking happen if you read 
the voice position then peek the address then wait for a small amount of 
time (small wait substituted for drawing to the screen?  My *speculative* 
theory is that the reading of the voice position register is happening at a 
regular frequency and that once in a while the reading (by you)  with the 
reading of the voice position by the GF1 (kind of like a beat frequency 
thing).  It may be the peeking instead of the reading that is conflicting 
with the GF1's access of the memory.

>Is there perhaps a better way of drawing a scope on the screen???
>Obviously all the sample data is in GUS RAM so I will definitely
>need to peek it.

Well, you'd probably have to use XMS, but you could keep a 1 MB buffer in 
the PC's memory that was an exact copy of the GUS's memory.  This may not 
help if it is the reading of the VP that is causing your squeaking, though.

>Thanks for any input.

I don't know if these ideas will help, but your welcome!

Dave

P.S. Yes, I'm still working on GusDelay, but not as much as I would like...

David MacMahon
Software Engineer
davidm@marcam.com

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