Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!csn!boulder!tcr!a68k!Edward_Braswell From: Edward_Braswell@a68k.UUCP (Edward Braswell) Newsgroups: comp.sys.amiga.hardware Subject: Accellerator Hack Message-ID: Date: 4 Jun 91 05:11:06 GMT Organization: The Arvada 68K BBS Lines: 57 Some of you may remember the old "14 MHz Hack" that's been floating around for A500's (and presumably A2000's). After MUCH! trying, I finally decided it wouldn't work for the A1000, due to differences in timing, in that the A1000 uses a couple of 74F74's and some other logic to generate it's 7M clock for the 68000, while the A500 has all of that stuff integrated into the "Fat Agnus" chip. But, I did find an accellerator that does work. It's not 14 MHz, it's only 8 MHz (7.14 -> 8 MHz => 12% increase in speed). And, it only cost me $2.50 for a 32 MHz crystal oscillator. In checking with the program RAMSpeed (and using a 68010), it gave me the following benchmarks: Clock: 8.209 MHz Chip Ram: 7.747 MHz Fast Ram: 7.519 MHz (My "Fast" ram board apparently has 1 wait state) F80000 Ram: 7.776 MHz (This is the 256K of fast ram ya get from placing Kickstart in EPROMS) The program SYSINFO gave the following "comparisons:" A 500 Standard: 1.54 B 2000 w/ Fast: 1.17 I'm not sure why a standard A500 is so slow, possibly that is for ALL CHIP ram and no fast ram. With the B 2000 (A 2000), you can see the difference. 17% faster breaks down to 5% from having a 68010, and 12% due to running at 8 MHz. What I did was place the 32 MHz clock onto lines from the RGB out connector for EXternalCLocKIN, EXCLKENable, +5 volts, and ground. I places a switch between ground and both the EXCLKEN and the ground for the crystal itself, as the Enable is "Active Low". With the switch, I can switch from normal to FAST and back "On The Fly" with no problems! Actually, there _IS_ one small problem with this hack: while in the fast mode, the RGB and video outputs are UNREADABLE. The screens get very messed up, as their Syncs are not at the specified NTSC frequencies, and my monitors can't "sync up". OK, yes, this is a major problem, but there are 2 solutions: 1. Modify the monitors so that they CAN sync with the new speed. 2. Use FAST mode blind. Yes, I know, what's the use of an accellerator if you can't see an output? Well, one use is for things you don't need to see, like ray-tracing. If you're doing heavy-duty ray tracing on an unaccellerated 68000 system, then the FAST mode would cut the time by 12% (and getting a 68010 would bring the saving to 17%!). Let's say the picture would normally take 2 hours to draw. You could save 15 minutes! Another good use for it is in LZHing / UN LZHing / Warping / unwarping, etc.. large files. If you don't mind waiting until it's done to see anything, this hack will save you time. Ultimately, what can you expect from a $2.50 accellerator? I think it's a bargain. Oh, if anyone wants specific pin outs / schematic, just ask and I'll upload them.