Elladan:
> 
> The number of ms till the next vblank will be a number between 0 and 17,
> usually nor more than 12 or so.  It cannot be accurate to more than 3ms
> or so if it comes from the X server.  The minimum time most systems can
> sleep is on the order of 10ms, and the precision they can sleep at is
> also on the order of 10ms.
> 
> This isn't powerful enough for *any* purpose as far as I can see.

Well, I can see plenty of purposes it is powerful enough for.
F.ex. retracing of the screen without causing flicker. A screen update
can be timed, and positioned in time as to minimalize the collision
with the screen update. F.ex. if the screen retrace time is 15ms, and
drawing on that screen takes 20ms, and the drawing starts when the
screen is traced about halfway, then the bottom of the drawing of the
pixmap will reach the bottom of the screen a little after the screen
starts to retrace from the top, thus avoiding flicker.

  | \
  \  \
   |  \
   \   \
\   |
 \  \
  \  |
   \ \


However, if what you want is to emulate an Amiga with its COPPER and
CLIPPER chips which were specially built for precise cathode ray
position based operations, I suggest you give up on interrupt based
stuff, and instead just renter an Amiga screen in 24 bit per pixel.

Kim0

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