Yes the reason for going for a 33MHz system bus is pretty simple... FP dynamic chip Ram will clock at that... but higher speeds are a problem... needing the move to SDRAM...which is why PC's did. So the idea was just to make the new custom chips go as fast as cheap chip ram would allow. But actually the speeds for this project are not important.. For starters it would be best just to use stock ST speeds.. 8MHz to get everything working.
I haven't mentioned SDRAM as the controller is more difficult and not simply a re-engineered existing custom chip. Besides... SDRAM may be dead soon.. the PC world moves fast. DDR ram is now cheap and Rambus is not far behind. FP Chip ram is standard logic however and will most likely be available for a long time.
newer CPLD's have a high enough gate count to host a complete 68000 chip plus other logic however last time I looked their speed ratings were in the 150MHz to 200MHz range. So thats where my 150MHz CPU clock figure came from. In fact if I had to guess now... probably most of the custom chips would go onto a single CPLD. Small amounts of Cache Ram should be available in these speeds.
OK... so how to develop this ? How to re-engineer the atari ST?
Well... 3 (or is it 2?) ways...
1. Write VHDL descriptions for the logic chips and synthesize them... and program the chips. To test ..depending on how big your testicles are ... have your old ST ready... pull the custom chip.. and put the CPLD version in.. run some test code.
OR
2. Do the above.. but instead of blowing up your atari everytime you make a bad logic chip... use an old PC and make a simple ISA card with an original logic chip on it.. write a piece of PC-DOS test code for it.. pull the chip.. place the CPLD version in...run the test code.
OR
3. Forget about VHDL if not willing to come to grips with it.. or its too expensive to get into... and sit down with a bag of logic chips and start designing each chip on a piece of stripboard... just like the original! then either test in a ST (as 1 above) or test it in the ISA card (as 2 above). Easy to convert then to programmable logic.
.. and in the end.. when everything works... sit down with a cad program and start laying the atx mobo tracks..
So first off... what we need is some custom chipset test code?... I've seen those original atari manufacturing test cartridges for the ST advertised (maybe Best Electronics?).. but has anyone seen anything similar available for download that has source code?
What would such a free ST be called? freeST? STif (ST is free) :P
