Re: [stella] Demo...

Subject: Re: [stella] Demo...
From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney)
Date: Tue, 26 May 1998 01:55:13 GMT
>After looking at your code, I don't think it has anything to do
>with PAL timing. It seems to be the problem with WSYNC taking
>more than 3 cycles to perform. I don't remember the exact timing,
>but I think Eric has posted about this some time ago. If you
>do a WSYNC after cycle 70, it would spill into the next scanline.
>In your sprite display routine, you seem to do the WSYNC pretty
>late in the scanline. That seems to be the problem.

I don't remember exactly offhand, but I think it's that the WSYNC can begin
no later than cycle 72 during a scanline.  If it begins on cycle 73 or 74
(thus its last cycle will be cycle 75 or 76), it does not catch the end of
the current line and waits until the end of the *next* line.  I *think*
this is because the WSYNC signal is high during cycles 75 and 76, and the
instruction waits for a leading edge and then a trailing edge of the
WSYNC.... so the instruction doesn't see the leading edge if the
instruction finishes during 75 or 76.

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