Re: Legacy I/O ports and text mode

On Jul 25, 2005, at 6:39 PM, Oliver Schwartz wrote:

>> Then I included the same code into Cromwell, but nothing happened.
>> I have no idea why - perhaps the Linux framebuffer driver "xboxfb"
>> does some setup that is required? The driver does not seem to do
>> any Port- I?o anyway, but it does access many MMIO ports. Perhaps
>> someone can help?
>>
>>
>
> As far as I understand it the legacy IO registers are mirrored in the
> "PCIO" MMIO-ports. So basically all calls to VGA_WR08 and VGA_RD08
> that use the PCIO-ports could be done on the legacy ports as well,
> once they are active.
>

Yes.


> On the other hand that means that all the wonderfull stuff which is
> done using VGA_WR08 and VGA_RD08 in xboxfb may possibly influence the
> behaviour of the legacy ports.
>

Yes. But only accesses to ports like 0x3c3, 0x46e8, 0x102 should have  
an effect on whether the legacy ports are enabled or not. And 0x46e8  
and 0x102 probably have no equivalent in the MMIO space anyway.


> Another problem you may face sooner or later is the missing VGA BIOS,
> as it usually contains the font definition for text mode. So you'll
> have to find out how to supply your own font once the text mode is
> enabled.
>

Doesn't the VGA BIOS ( http://www.nongnu.org/vgabios/ ) that comes  
with Bochs solve all this? The docs say that it is quite Bochs- 
specific, but I have had a look at it and it does lots of stuff that  
should only be required by physical hardware (including code to turn  
on the legacy registers in several ways), so it seems to be based on  
code that had originally been written for real hardware.

Actually we could even try to use the VGA BIOS of the nForce 420 as- 
is. ;-)

   Michael



-------------------------------------------------------
SF.Net email is sponsored by: Discover Easy Linux Migration Strategies
from IBM. Find simple to follow Roadmaps, straightforward articles,
informative Webcasts and more! Get everything you need to get up to
speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click