Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!sdd.hp.com!mips!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.programmer Subject: Re: 68030 Message-ID: <20963@cbmvax.commodore.com> Date: 25 Apr 91 22:56:52 GMT References: <20863@cbmvax.commodore.com> <1991Apr24.075729.6741@starnet.uucp> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 42 In article <1991Apr24.075729.6741@starnet.uucp> sschaem@starnet.uucp (Stephan Schaem) writes: > > Another thing I found on a A2630. > My SCSI controler is not reconize when running in 68000 mode via the > A2630 boot menu (But work perfectly without the A2630). Don't know why that should be, the hard disk controller is out on the expansion bus. The most likely cause of such a problem would be when you have your hard disk partitions explicitly set up for FAST RAM (not just any RAM), and all your Fast RAM goes away when the A2630 memory disappears. This is an unlikely condition with any Amiga hard disk controller, though third parties may set things up differently as a default. One of the reasonably common expansion board listing tools should be able to tell you if the system has actually recognized the hard disk controller board. > Also, something about the 68030 but in the A3000.Why burst is turned > off for the data cache? or why does it cause a slow down? Under 1.3, only the I-Cache is turned on, because the OS only knows about the 68020, and it didn't have D-Cache or burst. Based on their benchmarks, the software people have found that data bursting probably slows things down as much as it helps, at least on the A3000. Burst mode is essentially an extended cache prefetch mode. When the 68030 reads a longword location, and cache bursting is enabled, it can get the next three longwords, modulo 4, very quickly. However, they don't get fetched in zero time, just "very quickly" (on the A3000, each bursted word is fetched 2.5x faster than a work fetched the normal random access memory way). Since this is a cache prefetch, these extra longwords are just put into the I or D cache, as appropriate. There's no guarantee that they'll ever be used before overwritten by the cache. Apparently, the testing has shown that data so prefetched isn't used enough to pay for the prefetch time. In other words, D-Cache burst slows things down. Now, it certainly won't slow down everything, and in fact, very simplistic articifial benchmarks probably see this effect less than real world software. Via the SetCPU or 2.0's CPU command, you're free to turn on D-Cache burst if you want to. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "That's me in the corner, that's me in the spotlight" -R.E.M.