Wow, this is a fun zombie. You've got to love the "tech threads" that have such a high speculation-to-action ratio... ;^)
It's all been hashed to death, of course, but here's a really ignorant take on the "could we run MacOS on Coldfire?" question... why not just do it, for crying out loud? It seems that this thread is just hopelessly bogged down with minutia such as how one could somehow adapt the Coldfire CPU so it could physically be used as an upgrade CPU for an existing Mac, which is putting the cart *way ahead* of the horse. Why not prove out the concept on existing hardware (like a PCI slot-equipped Coldfire demo board) first? That's what the Atari Coldfire people did, and got a version of the Atari TOS patched and booting on a demo board well before any of their custom hardware was available.
It's been mentioned in one of these threads before, but one of the beautiful things about the classic MacOS when thinking about a project like this is its level of device independence. Emulators such as BasiliskII run MacOS in a virtual environment which has very little in common with a real 68k Macintosh simply by patching the ROM image appropriately. It seems to me that the simplest way to do Mac-On-Coldfire would be to incorporate the "direct-execution" core of BasiliskII (as utilized on Amiga and other 68k platforms) into a "New World 68k" bootloader/kernel, incorporating the CK68Klib binary compatibility layer and with low-level drivers for disk and I/O devices borrowed from Linux/uClinux sources. All the software tinkertoys are there, and I imagine a competent and very knowledgeable hacker (IE, one of the maintainers of BasiliskII or Sheepshaver) could put them together in a few man-months of work.
The real question is whether the end result would really be workable. There are certain edge-case conditions of existing 680x0 code that CK68Klib doesn't handle, and whether MacOS uses them and if so whether it's practical to patch around them are all open questions. But clearly it should be possible to deduce the answers before running off deep into the fantasy land of constructing a 680x0 socket-compatible accelerator for existing Macs.
A suitable Coldfire demo board isn't cheap, mind you. You're probably looking at a couple thousand bucks. Ironically a better approach might be to use an Atari Coldfire board. It's not cheap either, at 599 Euros, and availability is a problem, but it might be the best game in town. Of course, it's probably worth pondering that fact for a while. Any product based on this "research", whether it be an accelerator board or a complete new PCI-equipped Coldfire psuedo-Mac, is unlikely to end up much cheaper than that.
$600-ish dollars is a lot of money for a 300Mhz computer. Such a thing might well run 68K Mac programs at speeds comparable to a 1Ghz+ G4 or 2Ghz Pentium running an emulator, but... either of those options costs a heck of a lot less. (I can't find any benchmarks, but I'd be *seriously* surprised if the Atari Coldfire boards run EmuTOS faster than even a semi-modern PC running ARAnyM.) So clearly, the *only* reason to do this would be for love. Are there really enough people out there with undying love and nostalgia for *specifically* 68K Macs that isn't satisfied by emulators to support such a project? I have no idea. The Amiga and Atari people were faced with the complete extinction of their platforms so sketchy and uneconomical low-volume-production hardware wizardry was the only option the hardcore fans had to keep their love alive. Macs didn't die, they evolved, so... is there a point? Eh, who knows. All I know is there's an awful lot of talking and very little action. ;^b
It's all been hashed to death, of course, but here's a really ignorant take on the "could we run MacOS on Coldfire?" question... why not just do it, for crying out loud? It seems that this thread is just hopelessly bogged down with minutia such as how one could somehow adapt the Coldfire CPU so it could physically be used as an upgrade CPU for an existing Mac, which is putting the cart *way ahead* of the horse. Why not prove out the concept on existing hardware (like a PCI slot-equipped Coldfire demo board) first? That's what the Atari Coldfire people did, and got a version of the Atari TOS patched and booting on a demo board well before any of their custom hardware was available.
It's been mentioned in one of these threads before, but one of the beautiful things about the classic MacOS when thinking about a project like this is its level of device independence. Emulators such as BasiliskII run MacOS in a virtual environment which has very little in common with a real 68k Macintosh simply by patching the ROM image appropriately. It seems to me that the simplest way to do Mac-On-Coldfire would be to incorporate the "direct-execution" core of BasiliskII (as utilized on Amiga and other 68k platforms) into a "New World 68k" bootloader/kernel, incorporating the CK68Klib binary compatibility layer and with low-level drivers for disk and I/O devices borrowed from Linux/uClinux sources. All the software tinkertoys are there, and I imagine a competent and very knowledgeable hacker (IE, one of the maintainers of BasiliskII or Sheepshaver) could put them together in a few man-months of work.
The real question is whether the end result would really be workable. There are certain edge-case conditions of existing 680x0 code that CK68Klib doesn't handle, and whether MacOS uses them and if so whether it's practical to patch around them are all open questions. But clearly it should be possible to deduce the answers before running off deep into the fantasy land of constructing a 680x0 socket-compatible accelerator for existing Macs.
A suitable Coldfire demo board isn't cheap, mind you. You're probably looking at a couple thousand bucks. Ironically a better approach might be to use an Atari Coldfire board. It's not cheap either, at 599 Euros, and availability is a problem, but it might be the best game in town. Of course, it's probably worth pondering that fact for a while. Any product based on this "research", whether it be an accelerator board or a complete new PCI-equipped Coldfire psuedo-Mac, is unlikely to end up much cheaper than that.
$600-ish dollars is a lot of money for a 300Mhz computer. Such a thing might well run 68K Mac programs at speeds comparable to a 1Ghz+ G4 or 2Ghz Pentium running an emulator, but... either of those options costs a heck of a lot less. (I can't find any benchmarks, but I'd be *seriously* surprised if the Atari Coldfire boards run EmuTOS faster than even a semi-modern PC running ARAnyM.) So clearly, the *only* reason to do this would be for love. Are there really enough people out there with undying love and nostalgia for *specifically* 68K Macs that isn't satisfied by emulators to support such a project? I have no idea. The Amiga and Atari people were faced with the complete extinction of their platforms so sketchy and uneconomical low-volume-production hardware wizardry was the only option the hardcore fans had to keep their love alive. Macs didn't die, they evolved, so... is there a point? Eh, who knows. All I know is there's an awful lot of talking and very little action. ;^b