Path: utzoo!yunexus!ists!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!usc!apple!sun-barr!newstop!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Bus Latency
Keywords: bus dma latency
Message-ID: <128061@sun.Eng.Sun.COM>
Date: 17 Nov 89 23:12:13 GMT
Article-I.D.: sun.128061
References: <322@blenheim.nsc.com>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 18

In article <322@blenheim.nsc.com> waggoner@dtg.nsc.com (Mark Waggoner) writes:
> ... The recent postings about dma vs. non-dma disk controllers mention 
> that dma can be locked out for a long time when an overscan screen is 
> being displayed, but how long is "a >long time?"

Given a 704 X 440 screen with some sprites, audio, copper and blitter 
activity I'm pretty sure it is possible to lock out DMA for one full frame, 
14mS at 60Hz. 
	Frame time = 16.6 mS but chip activity is concentrated during
	the (220lines/frame)/(60 frames/second * 262.5 max lines/frame)
	which equals 13.9 mS. 

That would be slightly longer for PAL systems. 

--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@Eng.Sun.COM
These opinions are my own and no one elses, but you knew that didn't you.
"If it didn't have bones in it, it wouldn't be crunchy now would it?!"