testbios and the system timer

Richard Smith rsmith at bitworks.com
Tue Jun 8 11:58:00 CEST 2004

Eric W. Biederman wrote:

>>No. It allows full access to all IO ports. Otherwise it would have never been
>>able to get to the system timer.
> I was afraid of that.
>>So not only will it have to emulate x86 instructions it will have to emulate
>>some of the generic x86 hardware setup.
> Exactly.  But in this case emulation is more predictable than making
> certain your hardware is setup in a legacy conforming mode.

Hey, I'm totaly in agreement with you.  No convincing necessary. *grin*

It probally dosen't have to go all the way emulating a legacy PC 
enviroment but it looks like a few things will have to be dealt with. 
Restricting IO to legacy VGA registers and the allocated card IO 
locations is a good idea.  That should flush out any other issues of 
this sort.  There probally aren't that many though.

In other news I recompiled my VBIOS with the delay routine just doing a 
'ret' rathen then all that crazy timer stuff and testbios now completes 
on my target rather than going into the infinite loop it did before.

Still don't get a signon message but it does do pretty much the same 
thing that ADLO+vbios does.  H & V sync with the timeings correct for 
text mode but only a black screen. So thats some progress.  Interesting 
to note that running the no-delay vbios on my desktop PCI works the same 
as with the delays.

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