H+V Blanking

[Alex Deucher]

On Thu, Mar 8, 2012 at 5:14 PM, Rashid Mustapha
<rashid.mustapha at gmail.com> wrote:
> Hello,
>
> I'm not very advanced with code, so browsing the source probably isn't
> going to help my question,
> which is more of a technical on for a hardware (thats my bag!) project
> I am working on.
>
> Does anyone know if and possibly what needs patching to allow the
> vertical and horizontal blanking
> periods to be reduced to zero? I am aware of reduced blanking, but I
> seem to have to leave at least
> one pixel.....old Radeon cards seem to be the kindest - not sure about
> newer ones.
>
> I am trying to use the VGA output as a general 8bit DAC, and it works
> except the corruption from the
> blanking is quite destructive.
>
> Anyone have any thoughts on if this is limited by card firmware, which
> might clamp the registers to zeros,
> or any other way, or particular cards that this may be possible?

Its not firmware at least on radeons.  Most likely the hw has some
minimum sensible level.  Are you manually programming the hw or trying
to do it via custom X modelines?

Alex