Subject: Re: Considering port to new processor
To: None <>
From: Thor Lancelot Simon <>
List: tech-ports
Date: 03/30/2001 13:17:07
On Fri, Mar 30, 2001 at 09:51:18AM -0800, Justin Wojdacki wrote:
> Warner Losh wrote:
> > 
> > Good luck.  It is very hard to get Unix running on a machine without
> > an mmu.
> >
> What functionality does the MMU generally need to provide to get UNIX 
> running on a machine? 

Hm.  Off the top of my head, there's only one real feature that MUST be
in the MMU hardware: it must be possible to define ranges of addresses
such that any access to those addresses will trap.  Oh, that, and the
CPU core has to be able to restart instructions after the kind of trap
that causes.

Given those, I *think* you could do all of the rest in software.  It'd be
slow as hell, but people did build machines with two 68000s (to get the
"restartable instructions" property) and not a heck of a lot more, and
those machines *did* run Unix.