On Sat, 28 Apr 2012, Rob Landley wrote:
> On 04/28/2012 08:09 AM, Greg Ungerer wrote:
> > On 04/28/2012 04:15 PM, Rob Landley wrote:
> >> On 04/27/2012 01:08 AM, Greg Ungerer wrote:
> >> Not having
> >> nommu support for i386 is one thing, but why can I boot a nommu arm
> >> under qemu?
> >
> > It has been done on ARM targets in the past. I don't know if any can
> > be compiled and work both ways currently in mainline.
>
> Considering that u-boot starts running before the mmu is set up, and
> doesn't always bother to enable cacheing (and thus _never_ sets up the
> MMU), I'd think it would have to work...
Running with caches disabled is the easy part ...
> >> (What's involved in nommu archiectural support? Running a dedicated
> >> single-process i386 system in 4 megs ram might get a bit easier if you
> >> don't need to spend memory on page tables, seems nice to have the
> >> _option_...)
> >
> > It would be very nice to have :-)
> > The difficulty depends on the architecture. On some architectures some
> > important details just work differently with or without the MMU enabled
> > (things like caches, interrupts, etc).
>
> Can you set the mmu into flat memory mode with everything running in
> ring 0 and a 1:1 mapping of all physical memory?
... since page tables are also used to specify caching behavior.
You don't want caching enabled for MMIO regions. Without MMU, you typically
use transparent translation regions (some kind of poor-man's MMU :-) to map
the RAM regions cacheable, and the MMIO regions uncached.
With kind regards,
Geert Uytterhoeven
Software Architect
Technology and Software Centre Europe
Sony Belgium, bijkantoor van Sony Europe Limited.
Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium
Phone: +32 (0)2 700 8453
Fax: +32 (0)2 700 8622
E-mail: geert.uytterhoe...@sonycom.com
Sony Europe Limited. A company registered in England and Wales.
Registered office: The Heights, Brooklands, Weybridge, Surrey. KT13 0XW.
United Kingdom
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