[stella] WSYNC again (3 or 5 clocks?)

Subject: [stella] WSYNC again (3 or 5 clocks?)
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Sat, 29 Jul 2000 00:23:06 +0200
There was a discussion about WSYNC before. Because i had (and have) no access to hardware where i 
could test this, i had to believe that WSYNC needs 5 instead of the normal 3 clocks. 

But my name is Thomas and i have to see before i believe anything.

So i slightly modifieded the code of the latest z26-release (v1.37). I changed the execution time for WSYNC to 5:

*** TIAWrite.asm: ***
;just one added line of code:
  add [RClock],2                 ; WSYNC needs extra clocks! Does it???
  cmp [RClock],CYCLESPERSCANLINE ; did WSYNC come after end of line?
  ja  SetSkip                    ;  yes, skip a line (** check this **)

Then i tested the patched emu with many games (River Raid, Atlantis, Pole Position, Oystron, TPS...) and all of them now displayed wrong (especially the scores, see River Raid!)

I used the trace mode, and when i looked at the logged code, it showed, that sometimes WSYNC started exactly 3 cycles before the end of a scanline. So when i changed the emu code, it had to skip those lines.

I also tried 4 cycles and there where still some errors.

If i'm not completely wrong, this little experiment should show, that WSYNC only needs 3(!) clocks.

Did anybody try a well timed routine and tested WSYNC? Are you absolutely sure?? If yes, where
am i wrong?

Help me please!

Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |
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