Re: [Qemu-devel] [PATCH 14/17] lm32: todo and documentation

[Blue Swirl]

On Sat, Feb 12, 2011 at 12:45 AM, Michael Walle <address@hidden> wrote:
> Am Freitag 11 Februar 2011, 21:41:14 schrieb Blue Swirl:
>> > +Special instructions
>> > +--------------------
>> > +The translation recognizes one special instruction to halt the cpu:
>> > +  and r0, r0, r0
>> > +On real hardware this instruction is a nop. It is not used by GCC and
>> > +should (hopefully) not be used within hand-crafted assembly.
>> > +Insert this instruction in your idle loop to reduce the cpu load on the
>> > +host.
>>
>> It would be better to use MMIO or privileged instruction for this
>> instead of changing an unprivileged instruction.
>
> MMIO can't be used as that would have an impact on real hardware? The idea is
> to use this instruction for both the real hardware and QEMU.

Then it's OK. In general, if this were a QEMU only solution (like I
thought), then new instruction would have been a bit less attractive
than MMIO, which can be ignored on real HW, remapped by a kernel with
MMU (which you don't have) etc.