Prelim. idea for 68k 'upgrade'...maybe?

[Generale]

Okay, heres an idea I came up with a while ago to add extra features to a c64's cpu. Never tried it though. I don't see why the same idea couldn't apply to 68k.

For starters, the main difference is that the newer CPUs have more abilities, most notably the 32 bit databus, the mmu and the fpu.

Considering the a500 is a 16 bit databus and the 68k has it's 32 bit bus multiplexed internally anyway, the alterations that need to be done would be the extra opcodes (relatively easy), the FPU (moderate) and the MMU (depending on the desired CPU result...very hard)

For a hardware only solution without software patches, some odd kludges can be done...I believe.

Opcodes: They all go via ROMs. The output mostly mirroring the input, except for the new opcodes.
For these new opcodes, a different opcode is sent to the CPU such as a simple add for example, utilizing the memory accesses for the new opcode.
This saves extra wiring for the addresslines. (a buffer would be placed on the datalines to 'mute' the cpu) The PIC, FPGA or whatever intervenes as a result of databit(s) in the ROM allocated to the control of the 'custom' chip. This could do something such as say "grab the data from the bus on clock tick a, mess with the bits, then send them off on clock tick b ( when the cpu is going to do the write).

Anyway, that's the beginning of my idea. Please feel free to find faults as I'm sure it's a terrible idea anyway.

[Generale]

What's the point indeed... I never said that it was a totally practical idea  :-)
The extra opcodes are basically just the ones to do with mmu and mathematical functions. And yes they would be true to 68k.

As for the performance increase, not much. But it would add compatibility, but probably no more than a simple interrupt handler patch.

Are there fpgas with enough uhh gate thingies to do a 68k? I know there's enough to do a 65816 (re: c= one which i'd kill to get)

As for the dynamic recompilation etc, none needed. What I came up with is a brutal hack. And yes it probably would be a lot easier to use another CPU and plonk it on a board and just write a simple CPU emulator for it.

Oh yeah. The pseudo FPU would be a simple extension to the idea. And as for MMUs, they give me a headache, but easy enough to emulate.

I know it's impossible, but I wish I could use a dragonball EZ or VZ for the CPU.

That's right, I dl'ed the file up there. I'd better have a look.

[Generale]

I'm actually tempted to attack one of my surplus c=64s to test the basics of my idea.
The C64 because I have 5, or something like that of them. Now to get back to trying to figure out how to get my cd-rom to work on my a500.

[Generale]

hmm. I might leave the cpu for now. I've always wanted to play with FPGAs. Only problem is that the programming hardware and the fpgas are quite costly.What I don't get is why the programming hardware is so complex when they are meant to be field programmable.

I brought up the dragonball because it'd have to be my fave 68k cpu. And then you have the built in hardware used for the LCD, which could possibly be used for other things. And the software controllable clock speed, to name a few features. Theres a lot to be said for a 'computer on a chip' that still uses external memory. anyway, I'm dreaming. Even the soldering would be way too hard. the pin spacing is like 0.0mm on those things. So tiny!!!

[Generale]

Ooh. So much more information!

I've been meaning to have a better look at VHDL.
It might be overkill, but I have the trial of protel DXP, which I believe can also do fpga simulation among about a billion other things.

If anyone else wants to play with it and is on dialup like myself, Protel will send you the trial CD for free. the only limitation is time. If you buy the full version, that means you are very rich. And you are getting sleeepy @_@ You feeeel the need to give me moooneeeeey....

That reminds me. Circuitmaker 2000 is great for people that want to learn about circuitry etc. But not too hot at other things. They dnt have a fantastic range of chips, but its fun to play with.