🚀 go-pugleaf

Oh, no, cannot do without wait on retrace at all, regardless of how many
video pages you have (if your program is quick enough it can fill all
pages while first is displayed :-). And should be aware of some video
cards which doesn't switch page during display (they wait for retrace
to make the requested page active, before retrace they will not change
displayed page regardless of how many times program requests it),
I don't know what such a card does if page change is requested during
vertical retrace: display new page after end of retrace or display
once old ? I hope they display new...
And, about limiting time: can program timer interrupt to measure amount
of time requested by program and write servicing routine which switches
tasks; your program can 1. check how much time lasts vertical retrace
and how much time lasts displaying to determine how timer chip should
be programmed, 2. set timer interrupt service which waits for retrace
signal change, programs timer chip (note retrace and display times are
different, must reprogram rtimer chip on every interrupt) to get next
interrupt immediately before retrace signal change, and activates proper
task - display update during retrace, other (assume display updating
isn't the only what the program does ? :-) during display.
Note setjmp()/longjmp() can be used for task switching in TurboC.
For assembly programming - note every task must have own stack and
task switch is done by: save all registers on stack, save SS:SP in
task descriptor, load new SS:SP from new task descriptor, restore
registers from stack, return (registers can be saved in t.d., too).