Minix to the 68k?

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2 total messages Started by bandy Sat, 07 Feb 1987 00:57

#119

Author: bandy
Date: Sat, 07 Feb 1987 00:57

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Hi all, I'm sure that by now you've heard about Minix, and you're thinking
to yourself: "why didn't he write it for a decent machine in the first
place?"

Well, given his constraints, he did port it to a decent machine - there
isnt' a single cheap 68k system on the market that has a mmu in it, yet the
8086 family has had one since day one (well, not exactly an mmu, but it will
provide some protection against run-away programs if the compiler doesn't
generate instructions that twiddle the segment registers).

Anyhow, in order for us to do a 68k port we could do one(?) of the following:

1) Retro-fit some sort of mmu (68451? (ugh)) onto the boxes -- those of us
   whose cpu card's manufacturer had a little foresight might even have
   space for a socket for this beastie.

2) Hack up Stallman's gnu c compiler so it will generate PIC (but what to
   do when you take the address of a variable on the stack?)

3) Fit all the programs together like the Amiga does.

4) Physically separate kernel memory from user memory and then move each
   user process to its execution location whenever it runs (ick).


Given that I'm a little shy on information about #3, I'd like to ask the
Amiga gurus here how the Amiga manages to do multitasking. (for that matter,
how does OS9 mangage it?)

Of course, we'll all have to write our own device drivers, but that
shouldn't be any novelty to us now, should it?


Also, I remember that AndyT. said that a friend of his was working on a port
to the ST..  I'll try to find out what method he's using.

	andy

Re: Minix to the 68k?

#127

Author: jejones
Date: Tue, 10 Feb 1987 14:18

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Hiya!  I think <mike and Steve Blasingame have described stuff at least
as well as I could, but I should mention also that there is hardware
that lets you protect portions of the address space without mapping it.
You can still fragment memory, but it's much harder for a runaway program
to trash the system or other folks' memory.  The ST and Amiga, as far as
I know, don't have the beast, so you get to live dangerously, but (1) as
<mike says, multitasking is more useful than single-tasking, and (2) there's
nothing about TOS or CP/M68K that makes programmers magically write perfect
code with no wild pointers.

		James Jones

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