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Re: Devices using VGA Palette snooping?



> > Can anyone identify some graphics devices which actually use the 
> > PCI VGA Palette Snoop feature?   
> 
> Yeah, a whole pile of ISA video-in-a-window and capture cards that used the
> original VGA Feature connector, such as the C&T "PC-TV" chips, the Sigma
> Designs Reel Magic card, etc.
> 
> If used with a PCI VGA, the PCI VGA has to be put into snoop mode so that the
> RAMDAC writes make it thru to the duplicate RAMDAC on these ISA cards.
> 
> -jrp

Are there any PCI cards or chips (excepting actual VGA graphics
controllers) that use this feature, or is this just an ISA bus
legacy support issue?  

If the system VGA controller lies behind a PCI-to-PCI bridge, then
it seems like the ISA cards are out of luck.  The PCI-to-PCI
bridge has to claim the palette cycles for the VGA controller, 
preventing the ISA bridge from claiming them for the ISA card.
The PCI-to-PCI bridge doesn't have a true "snoop" mode.
-- 
Rob Elliott     relliott@twisto.compaq.com    Houston, TX
?P@