Re: i945G 1280x768 sync polarity bug

On 6/13/06, Barry Scott <[email protected]> wrote:
> Tim Roberts wrote:
> > Barry Scott wrote:
> >
> >
> >> Using the Xfree86 4.6.0 i810 driver I'm seeing a problem with sync
> >> polarity setting.
> >>
> >> This modeline is required for 1280x768 mode:
> >>
> >> Modeline "1280x768"   79.30  1280 1335 1473 1665  768 769 772 793
> >> -hsync +vsync
> >>
> >> But the syncs, as shown on an oscilloscope are +hsync +vsync.
> >>
> >
> >
> > Does this matter any more?  I thought the relevance of sync polarity
> > ended in the middle of the Clinton administration.
> >
> Good question. We note that the EDID data wants these sync polarities.
> Does the monitor use the pulse widths or the polarity to tell one mode
> from another? We think that the polarity is used, but we are far from
> certain.
>
> >> Looking at the VBE code it seems that as long as the Flags are
> >> defined correctly by the driver then its down to the INT10 BIOS
> >> to set the syncs on the hardware.
> >>
> >> Do you think this is a BIOS bug or a driver bug?
> >>
> >
> >
> > It may be an expectations bug.  As you note, the Intel driver, like the
> > Savage driver, relies on the BIOS to set the mode.  The BIOS has a
> > limited set of video modes, with canned parameters for each timing.  It
> > is not infinitely variable.  If the BIOS thinks 1280x768 should have
> > positive syncs, then you are going to get positive syncs
> I'm using 915resolution to add 1280x768 and 1360x768 into the BIOS.
>
> It seems that if there is an entry in the BIOS for 1280x768 then the driver
> is happy to to call INT10 to pass in the timings and sync polarity data.
>
> If as you say the BIOS timings are the only ones used then what is the point
> of the INT10 call to pass in the timings?
>

I'm not familiar with the i810's bios interface, but no other chip
I've ever worked on has allowed me to specify exact timings via the
BIOS.  It's usually either a VESA mode number or a size and a refresh
rate.  I doubt the i810 is much different, especially since most i810
bioses don't even support modes like 1280x768 out of the box.

Alex

> Barry
>