[OpenBIOS] [Qemu-ppc] Running client with MMU off

[Alexander Graf]

On 25.06.14 12:40, BALATON Zoltan wrote:
> On Wed, 25 Jun 2014, BALATON Zoltan wrote:
>> ppc_store_sdr1: 0fe00000
>> helper_store_sr: reg=0 20000400 00000000
> [...]
>> helper_store_sr: reg=0 00000000 20000400
>> Raise exception at 0041cd00 => 00000003 (40000000)
>>
>> ^^^ This exception should not happen. It is trying to handle it but 
>> the handlers are not working yet and gets in an infinite loop. It 
>> boots if MMU is disabled while this part runs but MorphOS does not 
>> disable it yet and according to my oftest results they are enabled on 
>> Apple too. How does it work on real hardware and why does it fail on 
>> QEMU? (Note the the value of sr0 is identical to the one set by 
>> OpenBIOS and SDR1 is unchanged so translations via the page table 
>> should still work, shouldn't it?)
>
> I was mistaken about the values being the same as it is zeroing sr0. 
> So can this explain why translation via the page table fails after 
> this and why an ISI is generated? Why are the sr registers set up with 
> the values above by OpenBIOS? Could they be 0 instead?

SR registers are used to translate EAs to VAs. If you set them all to 0 
they would end up getting the same VSID.


Alex