[Coco] Assembly: timing, vsync

[Ricardo M. Ferreira]

Hi, all!

I have a couple of (possibly) related questions, I'd appreciate your 
comments.


1) "Timer"

 From what I read and tested on a Coco 2 emulator (Xroar), the "timer" 
at $0112:0113 seems to be updated after every screen refresh. So, it 
changes at 60 Hz on NTSC devices ("xroar -default-machine cocous"), and 
50 Hz on PAL ("xroar -default-machine coco").

I want to write a program that is time sensitive. Is this the only timer 
in the Coco 2? If so, is there any way for my program to figure out the 
timer frequency (if it is 50 Hz or 60 Hz)?


2) VSync / vertical sync / vertical refresh / field sync

When programming in assembly, how can I make my code wait for the right 
moment to change the visible graphics page?

 From what I read, I guess I could use interrupts for this -  but it 
seems that I could also use the timer above (probably updated by an IRQ, 
anyway) by entering a loop and waiting for its value to change. Does 
anybody have a better suggestion?


[]s!