🚀 go-pugleaf

>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.

egg@dstos3.dsto.gov.au writes:
>I beleive its not a good idea to use the vertical retrace interrupt because
> according to "Programmers Guide to PC and PS2 video systems" hardware
>interrupts on IRQ2 cannot be distinguished from Vertical interrupts. I'm not
>that cluey on the subject but if its in the book ??? Apparently bus versoins
>of the Microsoft mouse cause this problem, and possibly other hardware that
>use IRQ2.

This is true of any type of card, no two devices on the ISA bus can
generate the same IRQ.

ptran@watserv1.uwaterloo.ca (Phat H Tran) writes:
>I used to do quite a bit of low-level programming on the C64 and I remember
>back then, we had only one IRQ line.  But we used this one interrupt
>to do everything from I/O timing to raster synchronization.  Having only
>one IRQ line meant that we had to daisy chain all our service routines,
>and each would have to check various registers to see if the IRQ was
>indeed for it.

The problem is electrical, because of the way the ISA bus is designed
you risk serious damage if two devices on the bus share the same interrupt.

							Ross Ridge

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