Open Source Scanline Converter visibility tests on Atari ST/e
Here are some tests made with OSSC on the Atari STfm and Atari STe to determine
screen size for both graphics and background. All STfm wakeup states tested.
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TEST 1 - OVERSCAN SCREEN WIDTH (ST 230 BYTE)
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Machine 1 : Atari STfm (50.03 Hz VBL, all four wakestates tested)
Machine 2 : Atari STe (50.03 Hz VBL)
Hatari : 2017-08-13 development version (tested both ST and STe modes)
Videomode : 230 byte overscan with stabilization
Graphics width
Left border STfm WS1 : 51 pixels
Left border STfm WS2 : 48 pixels
Left border STfm WS3 : 51 pixels
Left border STfm WS4 : 49 pixels
Left border STe : 51 pixels
Left border Hatari : 48 pixels
Right border STfm WS1 : 42 pixels
Right border STfm WS2 : 41 pixels
Right border STfm WS3 : 42 pixels
Right border STfm WS4 : 41 pixels
Right border STe : 40 pixels
Right border Hatari : 44 pixels
----------------------:---------------------
STfm WS1 total : 51+320+42=413 pixels
STfm WS2 total : 48+320+41=409 pixels
STfm WS3 total : 51+320+42=413 pixels
STfm WS4 total : 49+320+41=410 pixels
STe total : 51+320+40=411 pixels
Hatari total : 48+320+44=412 pixels
Background colour width (measured above overscan lines, unaffected
by stabilization).
Left border background STfm WS1 : 51 pixels
Left border background STfm WS2 : 48 pixels
Left border background STfm WS3 : 51 pixels
Left border background STfm WS4 : 49 pixels
Left border background STe : 51 pixels
Left border Background Hatari : 48 pixels
Right border background STfm WS1 : ~51 pixels (measured with ruler)
Right border background STfm WS2 : ~55 pixels (measured with ruler)
Right border background STfm WS3 : ~53 pixels (measured with ruler)
Right border background STfm WS4 : ~54 pixels (measured with ruler)
Right border background STe : 49 pixels
Right border background Hatari : 48 pixels
---------------------------------:---------------------------------
STfm total background WS1 : 51+320+51=422 pixels
STfm total background WS2 : 48+320+55=423 pixels
STfm total background WS3 : 51+320+53=424 pixels
STfm total background WS4 : 49+320+54=423 pixels
STe total background : 51+320+49=420 pixels
Hatari total background : 48+320+48=416 pixels
Notes
- The image is shifted four pixels left compared to ST-LOW
The overscan code:
dcb.w 11,$4e71
move.b d7,$ffff8260.w ;3 71 Hz Left border
move.w d7,$ffff8260.w ;3 50 Hz
dcb.w 88,$4e71
move.w d7,$ffff820a.w ;3 60 Hz Right border
move.b d7,$ffff820a.w ;3 50 Hz
dcb.w 11,$4e71
move.b d7,$ffff8260.w ;3 71 Hz Stabilizer
move.w d7,$ffff8260.w ;3 50 Hz
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TEST 2 - OVERSCAN SCREEN WIDTH (STE 224 BYTE)
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Machine : Atari STe (50.03 Hz VBL)
Hatari : 2017-08-13
Videomode : 224 byte overscan without stabilization
Graphics width
Left border STe : 40 pixels
Left border Hatari : 40 pixels
Right border STe : 49 pixels
Right border Hatari : 48 pixels
--------------------:---------------------
STe total : 40+320+49=409 pixels
Hatari total : 40+320+48=408 pixels
Background colour width
Left border background STe : 48 pixels
Left border background Hatari : 48 pixels
Right border background STe : 49 pixels
Right border background Hatari : 48 pixels
-------------------------------:---------------------
STe total background : 48+320+49=417 pixels
Hatari total background : 48+320+48=416 pixels
Notes
- The image is shifted eight pixels right compared to ST-LOW
- 49 pixel right border graphics
The overscan code:
dcb.w 13,$4e71
move.b d7,$ffff8260.w ;3 71 Hz Left border
move.w d7,$ffff8260.w ;3 50 Hz
dcb.w 90,$4e71
move.w d7,$ffff820a.w ;3 60 Hz Right border
move.b d7,$ffff820a.w ;3 50 Hz
dcb.w 13,$4e71
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TEST 3 - TOP/LOWER SCREEN
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Machine #1 : Atari STfm (50.03 Hz VBL, all wakestates behave the same)
Machine #2 : Atari STe (50.03 Hz VBL)
Hatari : 2017-08-13 (both ST and STe modes)
Videomode : Top+lower border + HBL rasters for the very early lines
Graphics height
Top border STfm : 29 lines
Top border STe : 29 lines
Top border Hatari : 29 lines
Low border STfm : 45 lines
Low border STe : 45 lines
Low border Hatari : 45 lines
--------------------:----------------------
STe total height : 29+200+45+2=274 lines
STfm total height : 29+200+45+2=274 lines
Hatari total height : 29+200+42+2=274 lines
Background colour height
Top border STfm background : 9 lines (above graphics with top border open)
Top border STe background : 9 lines (above graphics with top border open)
Top border Hatari background : 0 lines
Low border STfm background : 2 lines (under 45 lines lower border)
Low border STe background : 2 lines (under 45 lines lower border)
Low border Hatari background : 2 lines (under 45 lines lower border)
-------------------------------:-----------------------------------------------
STfm total background height : 9+29+200+45+2=285 lines
STe total background height : 9+29+200+45+2=285 lines
Hatari total background height : 0+29+200+45+2=276 lines
Notes:
- OSSC limitations
Sadly the OSSC (FW 0.79) cut the image short at the bottom to only 273
lines. But from other tests we've seen 274 lines graphics and two more lines
with background colour, which we will assume is right
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ILLUSTRATIONS
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RED = no display of either graphics or background colour
BLUE = Background colour
GREEN = Graphics
PURPLE = VSYNC
YELLOW = VBLANK
CYAN = 9 scanlines that is possible to exploit with background
BLACK = Frame showing the normal 320x200 ST-LOW screen
The entire 512*313 frame is illustrated, the first visible scanline with
graphics is shown as 160 bytes (syncline).
Image #1
Atari STfm WS1 230 byte overscan
413*274 (graphics)
422*285 (background)
Image #2
Atari STfm WS2 230 byte overscan
409*274 (graphics)
423*285 (background)
Image #3
Atari STfm WS3 230 byte overscan
413*274 (graphics)
424*285 (background)
Image #4
Atari STfm WS4 230 byte overscan
410*274 (graphics)
423*285 (background)
Image #5
Atari STe 230 byte overscan
411*274 (graphics)
420*285 (background)
Image #6
Hatari 230 byte overscan
412*274 (graphics)
416*276 (background)
Image #7
Atari STe 224 byte overscan
409*274 (graphics)
417*285 (background)
Image #8
Hatari 224 byte overscan
408*274 (graphics)
416*276 (background)
