Re: [stella] Demo...

Subject: Re: [stella] Demo...
From: bwmott@xxxxxxxxxxxx
Date: Thu, 4 Jun 1998 09:45:36 -0400 (EDT)
> 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.

I've been looking into supporting this, however, i'm a little confused.
When I run ESCAPE.BIN under Stella the screen stretches just like a
real 2600, however, when I run it under PCAE the screen doesn't get 
stretched.

To try and figure this out I wrote a little test program to hit WSYNC
at various cycles.  What I found out is that if WSYNC is hit at cycle
76, the last cycle of the scanline, then no stretching occurs.  If 
WSYNC is hit at cycle 77 then stretching occurs.  

Do this seem correct?  If so Stella already supports it...

Brad

P.S. When I say hit at cycle 76 that means that the STA Wsync started at
     cycle 73

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Bradford W. Mott (bwmott@xxxxxxx)          Computer Science Department
http://www4.ncsu.edu/~bwmott/www           North Carolina State University
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