fyi this and a portion of pauls' answer have been added to the glossary under PCI for want of a better place: http://wiki.opengraphics.org/tiki-index.php?page=Glossary
let me know if you wish any changes, or better yet, feel free to have a go ;-) jb On 01/09/2007, Tom Sylla <[EMAIL PROTECTED]> wrote: > For the simple case that has been discussed the past week or so, the > answer is also simple: > > When the BIOS wants to find a VGA card, it does a PCI scan, and keeps > track of all the VGA classcode devices it finds. > > The BIOS "picks one" to use. This could just be the first one it > finds, or may be based on a setup option that says which to use > preferentially. If you have 2 VGA-class cards plugged in to one PCI > bus segment, each BIOS will have some way to decide on one. For the > one that gets "picked", the BIOS turns on its IO decoders in its > command register. *all the others are left off*. Then the BIOS goes > and does the PCI expansion ROM dance for that card, and the VGA BIOS > runs and initializes. There is only one place for the VGA I/O and > memory accesses to go, since all the non-primary VGA cards have IO > decode disabled. > > Later on, an OS can go do its own PCI scan, assign real BARs to the > non-primary VGA cards (or the BIOS may have done so), and run drivers > that can talk to them. > > The above case is complicated by bridges and VGA palette snooping, but > the PCI spec addresses those problems, too. It is, of course, > completely up to each BIOS vendor how complaint they are to the spec's > guidelines. Another complication for the BIOS is that it must do > whatever is necessary to make sure the VGA IO and memory accesses > actually get routed to the card it wants to use. > > You can get to this answer from the PCI spec and the PCI-PCI bridge > spec, or from the Mindshare PCI book. > _______________________________________________ > Open-graphics mailing list > [email protected] > http://lists.duskglow.com/mailman/listinfo/open-graphics > List service provided by Duskglow Consulting, LLC (www.duskglow.com) > _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
