[Open-graphics] From PCI to VGA registers

[Michael Meeuwisse]

On 10 Aug 2007, at 10:42, Attila Kinali wrote:

> The original way of doing things were, that the BIOS expected
> to have executable code at certain memory locations. This got
> later changed to some probing (IIRC some signature) at fixed
> memory positions.
>
> If you are old enough, you might remember that old ISA devices
> hat lots of jumpers or dip switches to set on which memory addresses
> the card should listen to.

Just barely, but yes, I remember them. Ah, when everything was so  
easy and straightforward :)

> I'm not sure whether the afore mentioned Ralf Browns Interrupt List
> explains how this works. If not, you have to look it up in some
> old PC books. The german "PC Intern" (by Michael Tischler)
> used to do a good job in that. But i guess that any better
> PC internal book from until mid 90s should do the job.

Ralfs' list afaik only tells you what interrupts do what, not how it  
internally 'really works'. I have some books here explaining those  
details. My problem is that once the BIOS jumps to the OS bootloader,  
the memory map has already been set up so I've never seen this being  
'organised' somewhere. The OS can then add and/or remove interrupts,  
but I've never seen it happen that memory mappings are altered in  
some way (real mode, I don't mean moving around in the page tables of  
protected mode). I don't know how to 'set this up' when the ROM is  
executed on boot, on the 'computer side' of things (not on the PCI  
card self, we can do whatever we want there). Or maybe I'm  
overcomplicating things and there's no such thing as a table of  
mappings.

Mike
www.wacco.mveas.com