AFAIK, not all video cards generate the vertical retrace interrupt.
Even worse, some BIOSes have a configuration option which instract the
BIOS NOT to assign an IRQ to the PCI video card.
I fully agree that the vertical retrace interrupt will be of great
value, but I wonder if it is really worth the trouble, because it might
be available in only few cards and systems at the end of the day...
Well, I may be wrong :-)
Kazu
>Say is there anyone that can add signal delivery to the /sys/dev/fb/vga.c?
>(For now any quick hack to the driver for delivering the signal will do )
>
>The context is from a posting to the xfree86 mailing list:
>
>
>[EMAIL PROTECTED] said:
>> You need to fit one event in per retrace. If you knew
>> the phase of the sampling clock with respect to the retrace
>> you could do that by skipping one sample then two then one, etc...
>> But we don't know the phase and if you do that with
>> arbitrary phase you end up sending two events in one retrace
>> and then skipping the next and it looks worse.
>> If we had a signal delivered at vertical retrace time, we could easily
>> sync the mouse rate with the video rate -- run the mouse events
>> through a simple filter and estimate mouse position at the vertical
>> retrace interval using some forward estimation.
>
>> Additionally, the vertical retrace signal could be used for the double
>> buffering extension to avoid tearing, and for the sync extension which
>> kinda wants this. And for many video cards which can't update
>> colormaps or cursor positions at other times without visible artifacts
>> on the screen.
>
>> It would take some kernel work though; the results might well be worth
>> the effort.
>
>> -keith
>
>I am too busy nowdays working :(
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