Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!cbatt!ihnp4!qantel!lll-lcc!lll-crg!rutgers!caip!cbmvax!grr
From: grr@cbmvax.cbm.UUCP (George Robbins)
Newsgroups: net.micro.amiga
Subject: Re: Who is stealing my cycles?
Message-ID: <797@cbmvax.cbmvax.cbm.UUCP>
Date: Sat, 27-Sep-86 15:59:13 EDT
Article-I.D.: cbmvax.797
Posted: Sat Sep 27 15:59:13 1986
Date-Received: Tue, 30-Sep-86 13:05:10 EDT
References: <858@navajo.STANFORD.EDU>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 32

In article <858@navajo.STANFORD.EDU> rokicki@navajo.STANFORD.EDU (Tomas Rokicki) writes:
>
>Well, folks, I have some bad news.  I wrote a test routine
>to see just exactly how many CPU cycles I was getting from
>my Amiga.  This routine was essentially nested dbra's:
>
...
>screen moved all the way down so it wasn't visible.  Still,
>between 8 and 17 percent of the CPU disappeared somewhere.
>
>So it's not that much, but I'm interested in what the machine could
>be possibly doing that eats the CPU.
>
>I have an explanation for the 17% figure; when run out of chip
>memory, the processor gets every other 3.6 MHz RAM slot.  Well,
>running at 7.2 MHz, occasionally it wants the odd slot (a dbra
>does two fetches but requires ten cycles, so it is guilty of
>this) so the processor must wait two cycles before it gets the
>bus.  But out of fast memory this shouldn't happen . . .
>
>What it comes down to is this; the fastest effective clock speed
>I have been able to get is 6.6MHz.  Not to bitch, but I wouldn't
>be upset to get more . . .
>
>-tom

First guess:  Did you account for wasted pre-fetch cycles on the branches?

-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|caip}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)