Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!rutgers!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: A3000 CPU Wars!! Message-ID: <22456@cbmvax.commodore.com> Date: 14 Jun 91 15:42:08 GMT References: <16888@helios.TAMU.EDU> <22190@cbmvax.commodore.com> <22301@cbmvax.commodore.com> <25432@well.sf.ca.us> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 68 In article <25432@well.sf.ca.us> pwappy@well.sf.ca.us (Jeff Walkup) writes: >In article (22301@cbmvax.commodore.com), daveh@cbmvax.commodore.com >(Dave Haynie) writes: >>First of all, as mentioned about a quadrillion times in this very >>group, a coprocessor board can, if designed properly, up the >>motherboard clock rate of a 16MHz A3000 to 25MHz. This works because >>it was designed to work that way. >Does this involve installing a new clock crystal on the motherboard? >Or does the motherboard use the co-pro.'s clock in this case? The coprocessor board supplies the clock. You adjust a few strip-post jumpers on the motherboard and it'll accept the two system clocks from the coprocessor slot rather than the motherboard. >>To use such a faster CPU to its fullest ability, though,the designer >>can stick a full speed cache or some faster 32 bit wide memory on the >>coprocessor board. >So it still sounds like an economically reasonable limit would be an >'040 running at 25MHz (for under $1000), since going any faster would >mean handling the sync problems and adding extra RAM on the board. Unlikely. Certainly the "cheap" '040 boards might be without extra memory, and certainly without external cache. But I'm certain some companies will build them as fast as Motorola can get their 68040s going. Also, it's not overly expensive to build a 68040 memory control circuit without any memory; just a couple of PALs and some additional board space (maybe $15-$20 extra, if you don't get too clever). The synchronization problems aren't all that much extra work; in fact, due to the speeds we're talking about here, it's just about as hard to get a purely synchronous board working as an asynchonous one. You have to be real careful about clock skews if you're trying to make a 68040 board fully synchronous to the A3000, even if it sources the clocks. >*However*, I can see someone making an '040 board at say 50MHz, and >having a small (512K) static RAM cache, that wouldn't be too expensive. That's what I've been thinking. You CAN do it that way, and it has some advantages. First of all, the cache will tend to speed up your CPUs operation everywhere. You can cache A3000 motherboard RAM (which many people will already have lots of before they add '040s) and any Zorro III RAM that comes along (memory on the Zorro III bus isn't quite as fast as on the motherboard, but it has advantages: there's room there for lots of memory, and you can be sure that a Zorro III card will work in all future high end slotted Amigas). In any case, its up to the designer. We made it flexible on purpose. It should make A3000 coprocessor boards much more interesting. The A2000 boards got kind of boring, they all wound up looking more or less like the A2630 (asynchronous design, 25MHz or more, DRAM, a hard disk controller on some). >Although the lack of many MB of super-fast 32-bit RAM might hamper the >speed a bit, I can see it really racing through raytracing and other >floating-point-intensive operations. With 128K-512K of cache, in addition to the '040's internal cache, you should be getting an excellent combined primary/secondary hit rate. Obviously, you aren't going to go as fast as with 0 wait state memory, but keep in mind you don't get close to 0 wait states at 25MHz, and by the time you're at 50MHz, you're lucky if the secondary cache doesn't have wait states of its own (the 68040, however, should make this easier than the '030 did). -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "This is my mistake. Let me make it good." -R.E.M.