[OpenBIOS] r638 - in trunk/openbios-devel/forth: bootstrap device

Mark Cave-Ayland mark.cave-ayland at siriusit.co.uk
Fri Dec 4 01:46:19 CET 2009

Tarl Neustaedter wrote:

>> Continuing to work on Milax, I've found out that the infinite loop bug 
>> I'm getting here is because of an MMU problem - two different virtual 
>> addresses appear to be mapped to the same physical address. 
> I believe that's legal. I know that OBP used to do that on sun4s systems.

Oh that's interesting to know; however in this case I'm fairly confident 
it's broken :(  What happens is that first the volume descriptor is read 
from the ISO image into a special buffer, and subsequent reads for file 
entries should then go into a different buffer. Unfortunately the 
subsequent reads into the second buffer seem to be mapped to the same 
memory location as the volume descriptor, and so they overwrite the 
volume descriptor causing things to get stuck in a tight loop because of 
incorrect descriptor values :(

I've actually verified this by changing a value in the second buffer and 
seeing the same change in the volume descriptor buffer...



Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
t: +44 870 608 0063

Sirius Labs: http://www.siriusit.co.uk/labs

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