On Tue, 25 Aug 98 23:05:19 EDT, I-Jong Lin wrote:
> > 
> > On Tue, 25 Aug 98 21:13:46 EDT, I-Jong Lin wrote:
> > > 
> > > The '040 definitely has its MMU off.  However, I'm unsure whether
> > > the initial '030 (pre-accelerator swithch) has its MMU off.  Well, actually, 
> > > I'm not too sure  -- before I asked a question to newsgroup whether logical 
> > > address 0 was equal to physical address 0 when netbsd hit the start symbol.
> > > And the general consensus was no, that was not true -> ergo, my belief that
> > > MMU in the '030 must be off. 
> > 
> > The answer "no" was "in general"; i.e. it may be yes under a
> > particular circumstance but you cannot generally guarantee that it is
> > always "yes" under any circumstance.  IOW, that may depend on the
> > machine you are talking about.  IIci and IIsi come to mind IIRC.
> 
> Hmm.  So, just limiting the discussion to my Mac IIcx, is the MMU
> on or off at the start of NetBSD?

IMO, you should not rely on either answer.  If it's necessary to know,
you should check the MMU status register's enable bit.

> 1. although the MMU registers in the '030 and '040 may have the same
> names, they are actually different ( at least that's what the data
> books on '030 and '040 tell me)

Yeah, but if you have 030's SRP and URP, you can at least trace the
page table by software.  You know the format and you know where it's
located, right?

> 2. the pages tables of an '030 and '040 are not necessarily compatible either.
>    the routines for the translation of these page tables is too much for me.

That's why I said "there's at least a way to reconstruct the mapping
from the page table in memory because you have access to the Root
Pointers".

> BTW, in the system extension source code that I have it seems that the reset 
> vector is located at *(void *)4 and the initial stack is at *(void *)0.

Oh, I sometimes get them mixed up. *shrug*

Ken