From: Erik Johnson <erik AT microware DOT com>
Date: Thu, 3 Jun 93 10:18:50 CDT
To: djgpp AT sun DOT soe DOT clarkson DOT edu, iclone!mjhostet AT cs DOT unm DOT edu
Subject: Re:  Want vbl interrupts

 	I posted about this once before, but I didn't see my own post so  
	perhaps it got lost.

	I need to arrange to have an arbitrary C function of mine called 60  
	times a second.  setitimer() doesn't seem to be supported.  I've  
	noticed that the PC has the appropriate VBL interrupt, but I do not  
	yet know enough about PC's to write this interrupt handler and  
	install it.  I have, however, written interrupt handlers on various  
	other machines.

	If someone could point me to the documentation I need (do I need to  
	buy Turbo C?), I can get to work on it.  My problem is that there are  
	so many PC books out there it is difficult to sort the trash from the  
	good stuff, and I don't really know how everything fits together with  
	the djgpp environment.

	If I get this written, I am willing to contribute this package to  
	djgpp as freeware.  On the other hand, there are certainly PC hackers  
	out there who could write this ten times faster than I could.  If  
	anyone wants to take a little time to throw this together, or even  
	just let me know what problems I am likely to encounter, I would  
	greatly appreciate it.

	-Mat

Try reading the rec.games.programmer news group.  There you would probably
hear that PCs (of the IBM compatable sort), do NOT have a vertical blank
interrupt that you can tie into.  Some graphics cards will allow you to do
this (I believe).  The way game programmers time things to the vertical
retrace is to actually poll and wait for the VB.  This may not help you
because you are looking for something to automatically execute a routine
on interrupt.  Coming from the Atari ST platform, I find this to be quite
a step in the non-forward direction.

Erik R Johnson     erik AT microware DOT com