Vsync on Glamo

Thomas White taw at bitwiz.org.uk
Mon Feb 16 18:40:41 CET 2009

On Thu, 12 Feb 2009 18:08:56 +0530
Andy Green <andy at openmoko.com> wrote:

> If there was an effort to synthesize a VSYNC interrupt on Glamo (the
> real thing doesn't exist), is there actually anyone who would use it?
> Trying to figure out whether to close this as WONTFIX or have a go at
> it.

I noticed the problems described in the ticket, e.g. tearing of the
green oscillating rectangle which appears during startup.  Sharp
vertical edges moving horizontally are of course the worst possible for
showing up tearing.

However, in that case, is it likely that it's more to do with the slow
video bus (combined with single-buffered, non-accelerated graphics)
than with the timings?  Any estimates of how long the synchronisation
interval would be?  If it's shorter than the time needed for a redraw,
then for single buffered graphics I can't see it making any

For the forthcoming 3D stuff, updates to the visible framebuffer will
be happening by a (fast) hardware blit (I don't pretend to understand
the more wider details of how/if X uses double buffering, but a blit
operation is normal for Mesa).  If there are tearing problems then,
then I think this an emulated vsync would be useful for us.  However, I
think it'd be better to cross that bridge when we get to it.

Has anyone noticed tearing with things that are definitely accelerated
using EXA?


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