Re: [hatari-devel] New SYNC release - new comment on emulation :)

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Le 05/07/2020 à 09:17, Nicolas Pomarède a écrit :
Le 05/07/2020 à 00:05, Troed Sångberg a écrit :
Hi all,

Common lore is that an Atari can display a maximum of 274 lines fullscreen. However, while that's indeed the number of lines available from first graphics line (DE active) to start of 50Hz VBLANK, it's possible to skip the start of VBLANK to gain an additional two lines of graphics (and 30 odd pixels or so of line 277 until VSYNC kicks in and forces an end to the graphics).

So, 276.

However, that's _graphics lines_. The top border starts earlier than the earliest possible graphics line, and in borders you can do raster effects etc. This is currently not emulated in Hatari, those 9 lines are not displayed.

So, 285

Today, at Sommarhack, I released a new SYNC screen that starts the top border even earlier than that, an additional 9 lines earlier. Still "only" border, so only raster effects possible, but it's still something supported by the hardware.

So, 294

Of course, seeing all these lines is difficult. My Dell 2001FP can, but I need to manually modify vpos up and down - cannot see all at the same time.

The reason this is possible is that the normal top border starts when 50Hz VBLANK ends. As could be expected, there's a 60Hz VBLANK end as well in GLUE. I simply trigger that one instead.



thanks for the explanation ; nice trick to switch to 60 Hz to display color 0 early :)

I will see if I can support this in Hatari soon ; I already started some changes some times ago to show the 285 colored lines, but didn't have time to complete yet due to overall lack of time. I hope I can resume more work on Hatari.


just to let you know that Hatari was updated to have a much more accurate emulation of the VBlank signal's position. It will now correctly detect the early switch on line 14 used to show more lines on the background.

As pointed in the other part of this thread, those extra lines won't be displayed for now, because Hatari needs a more flexible way to increase window's height. But at least the inner work of handling VBlank is now more accurate.

In my case, I also had a small program used to check VBlank on/off position by changing colors each line. At 50Hz, I could see VBlank was off at line 25, but at 60Hz my old CRT monitor only allowed to show lines starting at 21, which is not enough to see your rasters that start at line 14.


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