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Old 21 April 2015, 20:06   #41
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Join Date: Dec 2013
Location: Lake Havasu City, AZ
Posts: 406
Anything 040 specific can be made to work with the 020, with the exception of the MMU. The FPU can be completely emulated in software - the original MAC II machines had either a 68882 or nothing, in which case FPU calls are trapped and done in software. Likewise, even some of Apple's 040 machines used LC040's (MMU only, no FPU). There are some differences in the exception handling for the 040, but all in all, it's not a stretch to make the 020 core 040 compatible for anything that does not need the MMU. From a CPU core standpoint, implementing the 040's MMU is hands down easier than the 030, because the 030 has multiple translation table sizes and other oddities that came from the 68851. With the 040 its either 4k or 8K page, and that's it.
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