[Qemu-devel] ARM Big endian system emulation

[Qemu-devel] ARM Big endian system emulation

[Alexis Berlemont]

Hi,

I have a question concerning the system emulation features : what is missing 
in the implementation of qemu to get a system emulation of a big endian 
ARM1026 target (like qemu-armeb for user emulation) ?

Regards.

Alexis.

Re: [Qemu-devel] ARM Big endian system emulation

[Paul Brook]

> I have a question concerning the system emulation features : what is
> missing in the implementation of qemu to get a system emulation of a big
> endian ARM1026 target (like qemu-armeb for user emulation) ?

In theory most of the bits should be there. However I don't have big-endian 
hardware to test against, and don't know if linux supports big-endian mode on 
the hardware qemu emulates.

It's likely that many of the emulated devices get it wrong, because I've never 
made the effort to figure out what the correct behavior is.

Paul

Re: [Qemu-devel] ARM Big endian system emulation

[Alexis Berlemont]

Hi,

Many thanks for your answer.

> > I have a question concerning the system emulation features : what is
> > missing in the implementation of qemu to get a system emulation of a big
> > endian ARM1026 target (like qemu-armeb for user emulation) ?
>
> In theory most of the bits should be there. However I don't have big-endian
> hardware to test against, 

I had a look at the "integrator cp" user guide. This board and the related 
core modules are supposed to be able to work in big endian mode (even if some 
components are not compatible like the Ethernet controller).

Do you know some other big-endian platform ?

I do not understand one more issue: I do not guess how a real big-endian board 
can be useful. Is it for checking whether the Linux kernel is working in such 
a configuration ?

Best regards.

Alexis.

Re: [Qemu-devel] ARM Big endian system emulation

[Paul Brook]

> > In theory most of the bits should be there. However I don't have
> > big-endian hardware to test against,
>
> I had a look at the "integrator cp" user guide. This board and the related
> core modules are supposed to be able to work in big endian mode (even if
> some components are not compatible like the Ethernet controller).

Sort-of. The Integrator boards aren't really big-endian, they're a little 
endian board with a CPU that can switch endianness.

> Do you know some other big-endian platform ?

There are many big-endian platforms.

> I do not understand one more issue: I do not guess how a real big-endian
> board can be useful. Is it for checking whether the Linux kernel is working
> in such a configuration ?

I have very little confidence in linux actually working in big-endian mode on 
an integrator. I'd also expect some of the consequences to switching to 
big-endian mode to be non-obvious. Access to real hadware allows you to check 
whether you're hitting kernel bugs or qemu bugs.

Paul

Re: [Qemu-devel] ARM Big endian system emulation

[Lennert Buytenhek]

On Sat, Apr 28, 2007 at 01:23:36AM +0200, Alexis Berlemont wrote:

> Do you know some other big-endian platform ?

Mostly Intel IXP stuff.

Most ixp4xx used to run in big-endian mode (but a lot of them switched
to little-endian when the network driver was made to work in little-
endian mode), and most ixp2000 and ixp23xx systems these days are still
run in big-endian mode.