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Re: [Qemu-ppc] PPC: Which instruction to fetch at Power-On?

From: Alexander Graf
Subject: Re: [Qemu-ppc] PPC: Which instruction to fetch at Power-On?
Date: Thu, 28 Mar 2013 17:04:37 +0100

On 28.03.2013, at 16:10, Fabien Chouteau wrote:

> On 03/28/2013 12:46 PM, Alexander Graf wrote:
>> On 28.03.2013, at 12:42, Fabien Chouteau wrote:
>>> While working on a patch to remove env->hreset_excp_prefix, I'm looking
>>> at which instruction should be the fetched first at power-on. I'm lost
>>> in all the PPC version and configuration, can anyone (Alex :) can help
>>> me with this mess?
>> Phew - I'd say just keep the targets you don't know exactly as they are :). 
>> That way you at least don't break anything that wasn't broken before.
>> For the targets where you do know better (like 7x0), change its behavior to 
>> be correct according to the respective spec.
> Here's what I found in the UM of almost all the cores supported by QEMU:
> Every CPU should start at the hreset address (i.e. excp_prefix + 0x100).
> However, some cores don't have a hreset exception (4xx and Book E (e200,
> e500)), those cores start at 0xFFFF_FFFC.

At least the G5 and I think also more recent POWER CPUs have either a small 
command stream or a full blown service processor that initialize initial CPU 
state like the PC. So there, the CPU starts at a board defined address.

I don't think we need to worry too much about that for now though.


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