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

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 25/02/2024 à 21:39, Daniel Hedberg a écrit :
> Actually, a lot of Falcon demos sets a 50Hz vertical refresh rate on VGA 
> monitors by directly writing to the Videl hardware registers, while a 
> few uses the standard 60Hz VGA video mode. I'm afraid that forcing 60Hz 
> on VGA will break more demos than it will fix, as 50Hz on VGA is pretty 
> common. A better solution would of course be to emulate/respect the 
> Videl registers.


Hi

you're right about that, using the monitor type is not good.

I changed the code to use VFT at $ff82a2 and VC0 at $ff82c0 to compute 
the vertical freq for the current video mode.

VFreq = ( HFreq / (VFT+1) ) * 2

It's possible I don't handle all the cases at the moment, but it should 
give good default results (at least better than what was previously used 
by reading $ff820a in Falcon mode)

Thanks to Zerkman for providing an article about Videl he wrote in 
french ST Magazine 101
http://zerkman.sector1.fr/archive/videl.html

(and thanks to Anders Eriksson for reporting this to Zerkman :) )

Nicolas