[Open-graphics] Video interrupt enable/disable

[James Richard Tyrer]

Timothy Normand Miller wrote:
> Something we need to be able to do is enable the interrupt for video.
> Generally, we only need one interrupt per frame, so what we need to do
> is set the interrupt bit in one of the instructions at the end of the
> last active scanline.  The thing is, it's not adequate to make that a
> parameter to the programming function... we need to turn the interrupt
> on and off quite a lot, so what would be nice is to have another
> function to call that enables/disabled interrupts by rewriting the
> right instruction with the flag changed.  The problem is that we need
> to somehow keep track of which instruction this is, for multiple cards
> with more than one video head each.
> 
> Perhaps it would just be simpler to always set the interrupt in the
> right instruction and have a mask bit in the global config registers.
> 
Perhaps it would be even simpler to have two interrupts.  One as you 
describe -- a sync interrupt -- which could not be turned off,  A second 
for a service request which would be triggered by firmware on the board 
or the DMA controller.

Then the issue of turning the sync interrupt off and on is moved to the 
driver since the APIC Intel acronym == Advanced Programmable Interrupt 
Controller) on the motherboard already has the hardware to turn off 
(ignore) an interrupt.

-- 
JRT