Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!usc!julius.cs.uiuc.edu!apple!agate!shelby!rutgers!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.tech Subject: Re: asd Message-ID: <17018@cbmvax.commodore.com> Date: 2 Jan 91 21:56:37 GMT References: <925@boing.UUCP> <927@boing.UUCP> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 43 In article <927@boing.UUCP> dale@boing.UUCP (Dale Luck) writes: >In article (Mike (My Watch Has Windows) Meyer) writes: >>The blitter can make thing the blit happen as fast as memory can deal >>with it. All it takes for the 68020 to do that is for all the >>instructions to land in cache. >Are you implying that just because instructions land in the 020's cache >that they no longer take time to execute? I believe all the cache does >is act as a fast memory with access time of 2 clock cycles instead of 3 or >more for outside memory. Let's not confuse 68020 and 68030. With the '020, cache hits are certainly going to be noticed -- data and instruction fetches happen on the same internal bus. On the '030, the I and D buses are only in common on the memory side of each internal cache, so if all the instructions come from cache, you do get an overlap of cycles that does hide most of the I cache fetches. I don't think this is quite as effective as what you get on some of the more advanced Harvard machines like the 68040, but it's definitely there. >I believe the 020 is still held to 4 clock cycles to chip memory. On the 3000, the '030 access to Chip RAM is the same speed, four 7.16MHz clocks, minimum. >If the memory access is 32 bits however, and the address is on a 4 byte >boundary then it can get 32 bits at once. So this does even it out the speed >differential a bit. Sure, you can probably do some things faster. But anything that can be done as or nearly as well by the blitter should still be done by the blitter, at least assuming there's something useful out of Chip RAM for the '030 to do at the same time. >Dale Luck GfxBase/Boing, Inc. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "Don't worry, 'bout a thing. 'Cause every little thing, gonna be alright" -Bob Marley