🚀 go-pugleaf

I've heard many conflicting things about using the Vertical Retrace Interrupt -
like that it can't be used with any IBM VGA's (some say just IBM's ISA VGA
card - does such a thing exist?).

I checked Sutty and Blair, and it has the following on pg 85/86:

Vertical Retrace End (Index 11h)
.
.
Besides determining the end of the vertical retrace, this register also
controls other functions that can be useful for some applications.
Bit Definitions:
..
D5 - Enable Vertical Interrupt (0=enable)
..
o D5: A zero in Enable Vertical Interrupt will cause an interrupt to be
generated to the processor on interrupt line IRQ2 with every vertical retrace.
This can be used as an accurate 60hz interrupt (for animation, for instance).
Once a vertical interrupt is generated, the interrupt is latched on until it is
acknowledged.  Writing a zero to D4 (Clear Vertical Interrupt) will
acknowledge the interrupt.
..
It seems like this is available on EGA also.  I just don't understand how you
can write an interrupt driver when all you know is the IRQ number.  Before
I break out PC-Watch and try to locate this sucker, it would be cool if
somebody else could explain.

thanks..


-court