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Post by Tom Maneiro on Feb 24, 2007 21:44:03 GMT -5
I'm thinking in a crazy idea: how about build your own SegaCD? It would use the following:
- FPGAs (or salvaged pieces) for the main video/sound chips (since the 68K/Z80 can still be purchased, it does not need to be implemented on FPGA, but could be done for have a "Genesis-on-a-chip(tm)", leading to a pretty small PCB)
- An IDE controller to allow you to plug standard PC CD drives, up to 72X (say bye to load times, and hello to CD-RW development, or just throw any slim CD drive for an ultra-compact console)
- Multibank, flash BIOS (switch between your region and MultiBIOS with a simple switch, like modchips)
- Everything on a old MCD1 case? (or even better: in a original cartridge case?)
It's possible or not? Since the Genesis was widely cloned, it may be possible with the SegaCD...
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Post by jlf65 on Feb 25, 2007 16:22:10 GMT -5
Not only possible, but an interesting idea. ;D
An FPGA would work... you could use a smaller FPGA with separate CPUs, or use a larger FPGA and put the CPUs in it as well. Depends on how much work you wanted to do.
If you aren't too good with FPGA's, another solution (the one I would do myself if I were doing this), would be to use a ColdFire processor to simulate both the CPUs and the hardware. FreeScale makes ColdFire MCUs that have all kinds of interfaces that would be handy.
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Post by GiGaBiTe on Mar 1, 2007 20:07:27 GMT -5
I'd think it would be hard to make the sync work between the two 7.61 MHz and 12.5 MHz 68000's.
You could probably do something like dual 12.5 MHz, but some sega games have VDP corruption when the bus is faster than 7.61 MHz.
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Post by Tom Maneiro on Mar 3, 2007 21:41:44 GMT -5
Those VDP corruption issues could be a bug of the original VDP, if this is the case, a fixed/improved VDP could be implemented on the FPGAs.
If the issue is located at game code level, the synchonization will be a major pain, and there is litte that can be done for it.
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Post by jlf65 on Mar 4, 2007 1:21:04 GMT -5
Those VDP corruption issues could be a bug of the original VDP, if this is the case, a fixed/improved VDP could be implemented on the FPGAs. If the issue is located at game code level, the synchonization will be a major pain, and there is litte that can be done for it. If the synchronization was that much of an issue, you could always use two separate 68000's clocked at the proper speeds, switchable to higher speeds for software that supported full speed 68000. |
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Post by GiGaBiTe on Mar 4, 2007 19:03:40 GMT -5
Those VDP corruption issues could be a bug of the original VDP, if this is the case, a fixed/improved VDP could be implemented on the FPGAs. If the issue is located at game code level, the synchonization will be a major pain, and there is litte that can be done for it. In the Genesis case, I think it has a bit from column A and some from column B. The VDP in the genesis is essentially a heavily customized Texas Instruments graphics processor that wasn't that great to begin with. It was probably never designed to run above ~8 Mhz (ISA bus speed in older computers.) which could be one reason for display artifacts / corruption. There have been newer TI graphics processors after the one that sega licensed and modified that could probably run in some backwards compatibility mode with some effort that could potentially fix the glitches and bugs. You can also probably blame crappily coded games like "Super Hang On" (which I think uses ray tracing) for being designed to rely on the lag of the CPU to work instead of implementing a reliable timer. |
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