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A 68010 in a Lisa?

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jamesdenton:
Thanks, Ray. I figured you'd chime in with some technical reasons as to why it wouldn't be a drop-in replacement. Not that I expected it to be, mind you. Was just curious to see if/how it would fail.


--- Quote from: rayarachelian on July 16, 2019, 10:20:50 am ---So you're going to have some very low level OS hacking to do in order to get it to work.

--- End quote ---

Will likely forgo this route, as it is not my wheelhouse. Time to make a Bitcoin-mining app in 68000 assembly to run as a standalone app.

rayarachelian:

--- Quote ---Will likely forgo this route, as it is not my wheelhouse.
--- End quote ---

Don't give up so fast, writing emulators wasn't in my wheelhouse before I started either. Give it a try and see what happens.
The big question I have would be how would you detect what CPU is in there and decide which ISR to use, assuming you don't want to build specialized versions of these OSs.Maybe you can find a way to build a universal ISR. Not sure how MacOS does it, but from what I recall they have specific ROMs for specific models, but maybe there's a way.
Once you can do that, you might even be able to get an 020 or 030 in there.


--- Quote ---Time to make a Bitcoin-mining app in 68000 assembly to run as a standalone app.
--- End quote ---
Sure, that sounds like a *useful* thing to run on a Lisa, and if you can mine ~6 bitcoins at today's price, you could buy a Lisa 1 off ebay.  8)
Just be sure you first upgrade all the caps in the power supply.

rayarachelian:
D'oh you won't be able to use a 68008 as it won't have enough address lines. meh.

So if you are brave, I'd say try a 68020 - if you're going to have to modify the BUS ISR you might as well go big. I don't know if an 030 will work or not - it might, but for sure you wouldn't want an 040 as that likely is too far away from what the Lisa's busses can handle - unless you want to go the way of an XLerator card that holds its own RAM/ROM and just talks to the old hardware for I/O. but then you'll have to rebuild the custom Lisa MMU, or rewrite the OS MMU functions to use the 040's PMMU.

jamesdenton:
I thought an interesting experiment would be to straddle an Xlerator board with one of the '030 Mac Plus accelerators using a Killy Clip or something along those lines. I have a MicroMac card that supports Plus/Classic/SE, but is the SE variant and is missing one of the GALs used for the Plus (and the clip - it only has the PDS connector).

rayarachelian:
It could work, but the solution has to be both software and hardware, in theory you could make an 040 - or even an 060 run Lisa Office System, but significant portions of the kernel would need a rewrite.
I'd suggest building a new XLerator from scratch rather than adding a hack to a hack. I can disassemble the ISR and we can figure out how to make an 010 or 020 or whatever work. The MMU part will be harder, but it can be done too.
One of the biggest issues I see is that LOS doesn't seem to be 32 bit clean, in my most recent experiments with 1.2.7 I see it use the upper byte in both address registers and even in the PC, but I'm unsure in what way or for what purpose, likely it tags it with something like a PID or segment number or something. I don't know if the userland cares about this, which would mean, rewriting the supervisor/kernel parts would be possible, but otherwise, the machine will be limited to 2^24 or 16MB (which all things considered is a lot more than 2MB it has right now.)
Though, I think at this point, if you're going to go through all that trouble of designing an XLerator and making major OS changes, it may be worth going big and all the way and build a "Lisa 3" around an 040 or 060 or whatever the latest Freescale chip that's still being made, and add color and sound and ethernet, wifi, and USB, etc.

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