🚀 go-pugleaf

In article <1992Aug3.210504.57823@cc.usu.edu>, sl8nl@cc.usu.edu writes:
|> > detect the retrace with an interrupt, rather than polling for it.  I want to
|> > use this so I can flip screens for animation every retrace - I think this is
|> > how it's done?  If anyone has some source, I'd really appreciate it
|> 
|> Question:  If you set the retrace up as an interrupt (possible...by modifying
|> the timer interrupt to run at 60 times a second), wouldn't you still have
|> to poll for it.  For instance, the polling code sets a flag to true for the
|> retrace.  Wouldn't you still have to poll for this flag the same way to
|> poll for the retrace?
|> 
|> Josh

No Josh, your wrong.  Some VGA board create a vertical retrace interrupt
whenever they enter the retrace period.  A program would merely have to 
trap the interrupt to know when the retrace period is happening.  The 
program could carry on doing its own thing until it gets the interrupt,
then it can update the screen.  No polling required.
I don't think the timer interrupt trick would work, even though the 
interrupt could be generated 60Hz (or 70Hz), it still would not inform 
the program that it is a safe time to write to the VGA.

I have tried the retrace interrupt a little, without any real success,
an I would also like to know how to enable the retrace interrupt, and
how to signal to the VGA that the interrupt had been recieved.

     SPHINX


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