Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rutgers!ames!ucbcad!ucbvax!hoptoad!gnu From: gnu@hoptoad.uucp (John Gilmore) Newsgroups: comp.arch,comp.sys.m68k Subject: 68020 speeds and wait states Message-ID: <2106@hoptoad.uucp> Date: Fri, 8-May-87 19:03:52 EDT Article-I.D.: hoptoad.2106 Posted: Fri May 8 19:03:52 1987 Date-Received: Sat, 9-May-87 22:08:25 EDT References: <5635@shemp.UCLA.EDU> <1774@im4u.UUCP>, <814@killer.UUCP> <8003@utzoo.UUCP> Organization: Nebula Consultants in San Francisco Lines: 54 Xref: mnetor comp.arch:1224 comp.sys.m68k:462 > > according to the latest rumors the Pinnacle XL020/MPulse 20 runs a 68020 > > at 16MHz, 1 wait state. Supposedly John Bremsteller has been working on > > getting the 020 up to 25MHz with only 1 or 2 wait states. In article <8003@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: > You will forgive us, I trust, for not being too impressed... The Sun-2, > now obsolete, ran a 68K at 12MHz with no wait states. The early Sun-3 > models, starting to look dated, run a 68020 at 16MHz with 1.5 wait states > (how in @#$%@ do they get half a wait state?...). Actually, Sun-2's all ran at 10MHz with no wait states, using 64K RAMs (1MB per packed Multibus board). Today you could probably run the same design at 12MHz using faster 256K or 1MB RAMs. Indeed, the original SUN at Stanford was an 8MHz board which was goosed to the 10MHz Sun-1 as the first Sun Microsystems product. Early Sun-3's actually run 16.67MHz (60ns clock) at 1.5 wait states. The half wait state is done by generating the CPU clock with a fast PAL which stretches the cycle of interest to 90ns. Running at 1.5 wait states is actually a conservative design; it could probably have been done at 1 wait state (indeed, ISI did it that way) but after years of design-on-the-edge, there was some sentiment for making the Sun-3's easier to manufacture. The Sun-3/50 (the $5000 model) runs at 15MHz at 1 wait state, which comes out to almost the same speed (268ns versus 270ns memory cycles). But its video is refreshed from main memory, which eats cycles. If you shut off the video, it should run within a few percent of a 3/160. Sun's presentation at the introduction of the Sun-3/200 mentions these possibilities for running fast 68020's (I added the Mem Cyc column, which is calculated by adding 3 to the wait states and multiplying by the clock rate in ns): System Limit w/s Cyc/Inst Clock MIPS Mem Cyc 3/160 no cache Memory 1.5 8.0 16.67MHz 2.1 270 ns no cache Memory 2.0 8.6 20 MHz 2.3 250 no cache Memory 3.0 9.8 25 MHz 2.6 240 3/260 cache CPU bus 0.1 6.3 25 MHz 4.0 155 This is Bremsteller's proposed machine: no cache Memory 2.0 ??? 25 MHz ??? 200 If he can get his RAMs to consistently run 200ns cycles, he may have a winner. It will only win by 20-25% over the 3/160 (not double like the 3/260) but if he can build it and make it run, why not? I suspect he'd have more luck with the 68030 since it does burst fetches into cache, which can be fed quickly with static column RAMs without building a whole board full of cache like the 3/260. -- Copyright 1987 John Gilmore; you may redistribute only if your recipients may. (This is an effort to bend Stargate to work with Usenet, not against it.) {sun,ptsfa,lll-crg,ihnp4,ucbvax}!hoptoad!gnu gnu@ingres.berkeley.edu