Just another A3640 @ 50 MHz hack
After spending most of my weekends last year with debugging, reading docs, trying out new ideas again and again I was finally happy to finish a hobby project of mine - running the A3640 in my A3000 at a speed of 50 MHz. This was in summer last year and at that time I thought no one but me would be interested doubling the speed of a 20 year old processor card (in fact some people already started laughing at me when I told them how I spent most of my spare time). So I thought it's not worth publishing it..
But now I read on Amibay about a 50 MHz mod done by "SpeedGeek" for the A3640! Looks both of us came up with a similar idea - crazy, isn't it?
So just for the unlikely case of somebody having too much time left I added the documentation I made up as an attachment.
The hack was done using 40 MHz 68040 being overclocked by 10 MHz. I was using MC88915 PLL for clock generation along with an extra GAL22V10 for some additional logic modifications allowing me to keep all of the original PALs on the card. I've been only testing it in an A3000 desktop but it's working reliable there for about half a year now. I can't see any reason why it shouldn't work for an A4000 as well, but please don't make me responsible for blowing up your Amiga!
Don't try this hack in case you don't have access to a logic analyzer and a GAL programmer. Reading chapter 7 of the 68040 manual might be a good idea too.