[Coco] Timer interrupt frequency (50Hz vs 60 Hz)

[Alex Evans]

The trouble I see is that both hsync and hsync are IRQ though you can check
the pia to see which one fired. There is also the issue that servicing an
IRQ is not really fast because all of the registers are preserved.

On Thu, Mar 20, 2025, 20:33 RETRO Innovations via Coco <coco at maltedmedia.com>
wrote:

> On 3/20/2025 7:07 PM, Alex Evans via Coco wrote:
> > Yes, you can interrupt (IRQ) on hsync on any coco.
>
> So if you write:
>
> prep:
>
> //put 0 in NUM
>
> // put 0 in START
>
> //enable fsync
>
> // wait for START to equal 2
>
> // use NUM value to calc PAL or NTSC
>
>
> fsync_IRQ
>
> // increment START
>
> // if START = 1
>
> // zero out NUM, enable hsync, and return
>
> // else disable fsync and hsync and return
>
> hsync_IRQ:
>
> // increment NUM
>
> // return
>
> Would the above give you different numbers in NUM you could use to
> determine PAL/NTSC?
>
> Jim
>
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