Running Amiga Apps on a 68k Mac?

I just started working on a retrocomputing project that I find highly interesting, and I’m confident I’ll be able to complete it. There’s an open source clone of AmigaOS called AROS, which has been ported to several CPU architectures beyond the Motorola 680×0 line, including PowerPC, 32-bit and 64-bit Intel x86, and 32-bit ARM (little-endian and big-endian). AROS has been in development since 1995, and is now quite impressive and full-featured.

I recently realized that if AROS on ARM or x86 is able to run many AmigaOS programs by recompiling their source code, and if AROS on m68k aims for full binary compatibility, then that implies that well-behaved Amiga programs (those that don’t write directly to the custom chip registers) ought to be binary compatible with AROS ported to other m68k systems, such as 68030/040 Macs. How difficult would it be to port AROS to a Mac, then?

For simplicity’s sake, I’m using QEMU’s emulated Mac Quadra 800 as my target system, since I can generate a substitute Mac ROM using the AROS build scripts and then run qemu-system-m68k with that ROM instead of an Apple ROM. Unfortunately, I’ve never been able to boot QEMU using any of the “Quadra 800” ROMs I’ve found, and I’m wondering if the emulation is now too fast for Apple’s code or if there’s some other timing issue. No matter: once I write a few drivers for the Mac VIA timers and for serial debug output, I expect to see more results from my AROS ROM than from Apple’s.

How many Amiga apps are well-behaved? That’s an interesting question. None of the games and demos that boot from floppy and immediately turn off the OS and multitasking are going to work, unless they’re ported to use only OS calls, which implies they’ll then be much too slow to run on a stock 7 MHz Amiga. But many newer Amiga apps support 3rd-party graphics accelerator boards, and therefore they ought to work on a Mac port of AROS, if they run on AROS on a real Amiga.

Porting AROS to m68k Macs (and QEMU) will be a stepping stone to my real goal, which is to port AROS to run well on Stefany Allaire’s latest 32-bit retro computer, the A2560K-040V. Unlike the old Macs, this system has a real graphics engine, with sprites and tile graphics, an advanced audio subsystem that emulates the most popular computer audio chips of all time, and even includes some handy goodies you might not expect, like a fixed-point math block and a floating-point math block, to make up for the lack of an FPU on the 68040V CPU (too bad there’s no new stock of the full ‘040 or ‘060 CPUs).







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