Re: [hatari-devel] video freq set to 60 Hz instead of 50 Hz for Falcon VGA

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 26/02/2024 à 10:25, Nicolas Pomarède a écrit :
> Le 26/02/2024 à 00:01, Eero Tamminen a écrit :
> > Hi,
> >
> > According to Hatari Videl code:
> > https://git.tuxfamily.org/hatari/hatari.git/tree/src/falcon/videl.c?id=HEAD#n203
> >
> > There's video shifter Sync Mode register for the frequency (set by 
> > TOS, based on the current monitor type I assume).
> >
> > According to Compedium, bit 0 specifies external sync (genlock?), and 
> > bit 1 specifies 60 Hz.
>
>
> Hi
>
> there were some discussions about this in the thread "Sync byte on 
> Falcon" and thomas pushed this based on test on real HW :
>
> https://git.tuxfamily.org/hatari/hatari.git/commit/?id=96d7e168b8a79d9c0add5308e17ad89e952b1071
>
> But I'm not sure bit 1 is the only way to detect 50 or 60 Hz ; as 
> described in some videl howto's it possible to get freq up to 100 Hz 
> when using the VGA mode.
>
> I don't know how the bit in ff820a "mixes" with vga timings and in which 
> case it's "prioritary"

Looking at how TOS/EmuTOS work for the "vsetmode" call, it sets ff820a 
to 50 or 60 Hz depending on the PAL bit4, but it also sets VFT reg to a 
suitable value depending on the video mode and its vertical freq (pal or 
ntsc, rgb or vga)

also if vga mode is used with other freq such a 75 or 100 Hz, then 
ff820a is of course useless.

So, I don't really understand which of ff820a or ff82a2 is used to 
determine final vertical freq.

Anyone with videl's knowledge who could explain how it work ?

Nicolas