Steven Seagal's Atari ST Web Site


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"Steem Over Style"

  Development screen of Steem SSE 3.8.0  

Other fixes



The eye must not blink!

  Problem was E-clock timing synchronisation between VBI and ACIA. Or so it seemed. Anyway, there's no more flicker.  

  ACIA/IKBD transmission timings weren't as long as I thought. In compensation, I have to hack it for the Froggies Over The Fence menu, a mysterious case.  

  Quite messy but this is actually correct emulation. This program was buggy in its first version but it was the source of some Blitter emulation improvements: hog bit and some timings.

Update: had to walk back on some timings, because it broke something else.


  It worked in Steem 3.2, but it was trouble in the beta of v3.8 because when making ACIA timings more precise, some glitches would appear. It turned out that an MFP timing issue was just revealed. So in Steem SSE v3.8, it will still work but if you check option C1, then check C2 too.  

  Thanks to the demo We Were, we fixed two little issues.
1) Steem didn't render correctly when HSCROLL was changed early on in a scanline.
2) There's a little border of colour 0 visible in large display mode when a program uses the "line +20" Shifter trick. It wasn't correct in Steem SSE before, now it is.

  Also a STNICCC 2015 demo, this one by Nordlicht is very confusing. In STE mode, a spurious "line +2" effect would ruin the show every 4 frames. I needed a long time to get why it was so. The demo shifts the same screen 3 times by changing the palette. The "line +2" would make the screen bad only at the third shift.

Despite this nice detectiving, I couldn't really fix the "line +2", it's a hack.

  A good tester reported a bad scroller in World of Music by New Power Generation in STE mode.

I saw that on the real STE, the scroller staid smooth, only changing colour.



  This is how it looks on a real STE. The clown picture is shifted.  
  On an STF this should look like this:  

  The scroller staying in the same colour.

On the STE, the problem is a "line +2" triggered by a late switch back to 50hz after the lower border has been removed by a switch to 60hz, because timings are different on an STE, which is emulated in Steem SSE (if it looks better in other emulators, maybe they don't emulate this difference). It's quite frequent.

But a "line +2" by itself will destabilise the Shifter, there's one more word (2 bytes) loaded in it. This explains the shift of the picture above: the Shifter is destabilised at the lower overscan limit, and stays in that condition during the next frame.

  The beauty of this is that it also fixes the Nordlicht case (4th screenshot above), without a hack.

I'm not one to brag, but if you want to check STNICCC 2015 demos, you know which emulator to use.


  A quite confusing STE screen to get to correctly display. There's horizontal scrolling, on the fly change of the video counter and unstable overscan. So, let's use some hacks. In fact, some were already in use for XMAS 2004, there's some generality in those.  

  The insane programmer of this demo inadvertently told the STE to start and stop a DMA sound sample at the same address. For the STE, it actually means it will never stop instead. Steem was more civilised, but that was wrong.  


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