Subject: Re: Re(4): Port to 8xx embedded PPCs
To: None <,>
From: Randy Devol <>
List: tech-embed
Date: 06/20/2000 09:52:14
| On Mon, Jun 19, 2000, Ignatios Souvatzis <> wrote:
| >> Regarding the kernel, the MMU is different, so all the memory management
| >> stuff need probably a complete rewrite.
| >
| >how different is it, exactly?
| It has only TLBs, no hash table (a bit like the 603 but the TLBs and
| exception mecanisms are different). It provides a different set of
| special registers for use in those exceptions (TLB reload). The number of
| TLBs can be different between processor models. That's all I know for
| now, I didn't dive in the manual yet. But for example, linux/ppc uses
| completely different exception handlers for TLB reloads than it uses for
| 604-like (hash table based) or 603-like (TLB only) CPUs.

The 8xx TLBs are rather like 680x0 TLBs.  They are designed for reloading
from two-level tables in RAM.   Suffice it to say that almost no MMU code can 
be shared between the existing PPC port(s) and a new 8xx port.

BTW, I am most of the way through a port but have had to take time off to pay
bills.   The work I have done to date is not available for free, but it is
available. :-)

-=O=- Randy

In "A Scanner Darkly," was Philip K. Dick foreshadowing Web commerce:
"Someday, he thought, it'll be mandatory that we all sell the McDonald's 
hamburger as well as buy it; we'll sell it back and forth to each other 
forever from our living rooms."