Re: Kit-Based Lisa

Hi James, Kevin,

James MacPhail wrote:
> No, since it was designed circa 1983, the COP421 and the Lisa 2/10 version
> of the IWM are the only things that are a technical problem in the
> "proprietary behaviour" sense.
>

Kevin,

Both the COP421 and the IWM/6504 can be replaced by other controllers. Perhaps the COP421 can be replaced by something that handles USB mice and keyboards - and it would also need a clock chip.

The 6504/IWM combo can be replaced by another controller - with software that make it look like the original to the ROM and OS.

The 6504 can be told to go execute random routines, but there are only a handfull of these, and they can be detected. For example MacWorks sends code to the 6504 to detect whether a floppy is read only or read write. Not much else though. Look at LisaEm source code in floppy.c to see what's checked for. You wouldn't get floppy compatibility, but floppies can be disk images. See libdc42.c for a useful disk library.

You'll need a real 68000 chip, you can't use 68030's or dragonballs due to the exception handling. You could use another CPU, but it would have to emulate a 68000's stack frames. Perhaps you might be able to do a 68040 with a custom ROM that works like VMWare does - it would need to intercept any supervisor mode opcodes and emulate them.

The MMU is a custom job, built out of discrete components and not compatible with the PMMU chip.

Video is very simple, but you'd probably want to replace it with a simple frame buffer attached to an LCD instead of a CRT - any VESA VGA should work, but you'd need some sort of DMA controller to transfer memory from the Lisa to the VGA chip.

You'd also need to simulate the video state ROM's behavior and synchronize that with the video. You'd need real VIA6522's for I/O. You'd need a real Zilog 8530 for the SCC.

You'd need to decide what to do about expansion port slots. I suggest keeping to the spec of a real Lisa for HW compatibility, but you don't have to.

It's a hell of a lot of work. In some ways, more work than to build an emulator, in others, much easier.

Good luck. Received on 2008-03-17 22:02:38