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Old 17 October 2020, 00:04   #21
Don_Adan
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Originally Posted by DrBong View Post
Even if he wasn't, what could possibly warrant the time & energy spent on supporting obscure 68851-specific features under emulation?



Yeh, but only when you use assemblers on a military-spec Amiga 2000! Anyway, it was interesting to learn that even the 68010 had the possibility of adding an external MMU (68841)....but no home computer used it AFAIK.
Military A2000 with US Air Force flight simulator. Maybe also Mac II:

"I can answer the last part of your question: yes, the Mac II could use a 68851.

For a time, Virginia Tech required incoming Computer Science freshmen to purchase a (heavily discounted) Mac II running A/UX, Apple's first in-house-developed UNIX. These machines shipped with 2MB RAM, an 80MB HD (huge for the time), and a 68851 pre-installed; A/UX required the 68851 to work."

https://retrocomputing.stackexchange...mu-replacement
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Old 17 October 2020, 00:09   #22
DrBong
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@Don Adan
Read the last part of my post again....I was talking about the MC68841 (and not the 68851). I think the 68841 may have been used on workstations, but not home computers AFAIK as the 68010 didn't feature prominently on 68K home computers. I'm aware of the Mac-II and 68851 as I used Macs a lot in the late 80s and early/mid-90s at university.
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Old 17 October 2020, 01:16   #23
Don_Adan
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@Don Adan
Read the last part of my post again....I was talking about the MC68841 (and not the 68851). I think the 68841 may have been used on workstations, but not home computers AFAIK as the 68010 didn't feature prominently on 68K home computers. I'm aware of the Mac-II and 68851 as I used Macs a lot in the late 80s and early/mid-90s at university.
Maybe you have this flight simulator in your collection?

http://www.generationamiga.com/2016/...ered-by-amiga/
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Old 17 October 2020, 11:32   #24
Thomas Richter
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Originally Posted by Toni Wilen View Post
I don't think there are any Amiga programs that require 68851 or use 68851 features. First requirement for emulation some hardware: it needs software!
The mmu.library supports it, of course.
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Old 17 October 2020, 12:16   #25
Toni Wilen
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Re-read earlier replies. Lots of programs "support" 68851 = use it like 68030 without TTRs. No Amiga program (please, prove me wrong!) use 68851 features that are not in 68030 MMU. No Amiga program even uses all 68030 MMU features like page table limits.
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Old 17 October 2020, 13:15   #26
Thomas Richter
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Re-read earlier replies. Lots of programs "support" 68851 = use it like 68030 without TTRs. No Amiga program (please, prove me wrong!) use 68851 features that are not in 68030 MMU. No Amiga program even uses all 68030 MMU features like page table limits.
Not that I know of, at least. There are a couple of exotic features the PMMU supported, like modules and protection rings, even with support at the 68020 side via the CALLM instruction. Neither did MacOs use the PMMU. Some Unixoid systems that could run on it might, but probably only for paging (same as the mmu.lib).

Concerning the instruction, this is "test if breakpoint flag in PSR is clear, set register d1 if so". The PMMU had additional breakpoint support, but this was not very useful as you had to inject a special instruction into the code, and one could use the standard MC68K "illegal" instruction as well (as most debuggers do), with just a tiny little bit of extra services provided by the PMMU. Unclear why anyone would want that or need it.

As a question to the OP, where is this instruction sequence taken from?
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