Re: NTSC VIC-II timing

Date: Wed, 21 Jun 2017 18:25:24 +0200
Message-ID: <2804561.3dS9bJNANs@rakete>
On Wednesday 21 June 2017, 18:12:12 wrote:
> > On 2017-06-21, at 17:01, wrote:
> >> According to the famous document by Chris Bauer, there are three timing
> >> variants of the VIC-II. While PAL is always 63 cycles per  line, with
> >> NTSC
> >> there can be either 64 or 65 cycles per line and I am in fact able to
> >> reproduce the difference with -model ntsc and -model oldntsc in the
> >> current
> >> VICE.
> >> 
> >> The question (before I spend weekend on trial'n error counting cycles and
> >> possibly reinventing the hammer ;-) is: do we have ane established,
> >> reliable software method for detecting which NTSC VIC-II is installed in
> >> the machine? I guess it must have been done multiple times by now and
> >> used
> >> in some NTSC games/demos..
> > 
> > most demos or games probably dont care about detecting the difference - as
> > the 64 cycle VIC is extremely rare.
> Maybe I am impractical indeed, yet I can't envision a commercial product
> (game f.e.) that would just break because the machine has a different but
> still valid VIC chip inside.

but thats how it is :) or well perhaps not - it never was a real problem, 
because in the early days games wouldnt use anything that needs that perfect 
timing. and as said, the 64 cycles VIC is so rare, you can just ignore it.

that said - think of the "drean" PAL VIC - there is not one game that was 
fixed for it :)

> > however, iirc on codebase there are some detection routines.
> I found a routine on codebase that is supposed to distinguish between the
> NMOS and HMOS variants of the PAL VIC:
> interesting in its own if it works, but that's not what I need.
> > basically just count the cycles for a line (or a frame) using a CIA timer.
> Exactly what I meant with spending lots of time counting cycles ;-)

well, there is no other way :) it isnt a problem in practise though, imho


Trying to outsmart a compiler defeats much of the purpose of using one. 
<Kernighan & Plauger>

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Received on 2017-06-21 17:03:49

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