On 04/28/2012 04:15 PM, Rob Landley wrote:
On 04/27/2012 01:08 AM, Greg Ungerer wrote:
On 26/04/12 15:14, Rob Landley wrote:
I have also been able to boot an ARM noMMU kernel for the AT91x40 SoC
under SkyEye. This time, the userspace works fine. I haven't had the
time to clean up this, and it requires patches to both the kernel and
SkyEye to work properly. If you're interested, I'll give you these
patches and configs when I'm done with the cleanup.
I'm unlikely to play with skyeye (tried it once, but it was years ago).
Is there a strong reason nommu kernel's won't run on hardware or an
emulator that _does_ implement an mmu? (Can't it just not use it?)
No. It comes down to architectural support. There are a few that do
it. I have ColdFire hardware with MMU, it can be compiled and run
either with or without MMU enabled (by flicking the kernel's
CONFIG_MMU switch).
Architectural support in the kernel, or in the emulator?
In the kernel. For arches that don't currently do any non-mmu it is
usually the code in arch/foobar/mm and often some in arch/foobar/kernel
that has no concept of operating with the MMU turned off.
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.
(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).
Regards
Greg
------------------------------------------------------------------------
Greg Ungerer -- Principal Engineer EMAIL: g...@snapgear.com
SnapGear Group, McAfee PHONE: +61 7 3435 2888
8 Gardner Close, FAX: +61 7 3891 3630
Milton, QLD, 4064, Australia WEB: http://www.SnapGear.com
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