Date   : Tue, 12 Mar 2002 10:46:44 GMT
From   : Thomas Harte <thomasharte@...>
Subject: Re: A couple of CRTC/Timing problems

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> Secondly, I can't seem to get rid of that flipping "tidemark", 
you know that
> one scanline at the point where mode/pallette changes occur 
that always
> flickers... I've tried adjusting VIA timings, VSync delays.. 
nothing seems
> to be making it go away...

I don't want to assume anything about how your emulation 
works, but a common feature amongst emulators which 
perhaps BeebEm includes is to only accredit mode and palette 
changes at the end of the scanline. This often leads to the 
watermark line no matter how accurate the rest of your timing 
because the original program only cares to make its changes 
within the time between pixels stopping at the end of scanline 
and starting on the next, however the emulator uses an exact 
cut off point rather than a region. Of course you can try to 
make your cut off point at the exact end of the region, but 
perhaps the program hasn't quite finished making changes 
when the pixels begin and so on. Perhaps you are treating 
palette and mode changes outside of your inner loop, even if 
you are dealing with CRTC register changes inside?

Boast moment : ElectrEm (except WIP because I am part way 
through reduction of code duplication) accepts mode and 
palette changes mid scanline as originally intended, and has 
worked entirely correctly in the past with the only vertical split 
mode demo I've ever seen.

-Thomas
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