mirror of
https://github.com/joncampbell123/dosbox-x.git
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114 lines
3.9 KiB
Plaintext
114 lines
3.9 KiB
Plaintext
Project Angel
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Requirements:
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- xms=false (the demo will not start if HIMEM.SYS is present)
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- emm=false (the demo will not start if EMM386.EXE is present)
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- extended memory
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- realbig16=true (the demo apparently uses Flat Huge Real Mode i.e. jumping to real mode with B (big) set in code segment)
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- at least cycles count 12000
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- gus=true
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- machine=svga_s3 or machine=svga_et4000 (will not start with machine=vgaonly)
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- pit hack=project_angel_demo (this setting forces the PIT to fixed values that forces the demo to run and keep time properly)
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Note that the comments below apply to the demo when run without the PIT hack. The PIT hack forces the timer to tick
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at one of two time intervals in a way that forces the demo to run at the correct rate and helps prevent the demo
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from hanging at startup. For whatever reason, the PIT hack also resolves issues with music skipping forward during
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VGA mode changes, and eliminates the visible VGA tearline in the Mode-X parts.
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Demo comments:
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- This demo is very picky about timing. In fact, when you run the
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demo, one of three things will happen.
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1) The demo will hang
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2) The demo animations and music will play at 1/2 speed
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3) The demo will actually run at normal speed
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If it does manage to run at full speed, there is a chance that
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the demo will lose timing and suddenly run slow, or stop entirely.
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To put it another way, the reason this demo is so hard to run
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(besides the Huge Flat Real Mode hack) is that it is very picky
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with the PIT 0 system timer. If DOSBox's debug messages are
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correct, the demo is *constantly* fiddling with the PIT timer
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and flitting rapidly between 18.2Hz and about 400-520Hz. It seems
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to auto-adjust, to what exactly I don't know.
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You can discern from the PIT timer what happened to the demo:
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1) The demo will hang
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If DOSBox debug messages are compiled in, you will see:
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976659850: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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976747898: PIT:PIT 0 Timer at 22095.9628 Hz mode 3
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976775657: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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977921776: PIT:PIT 0 Timer at 7747.9351 Hz mode 3
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977994511: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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978082575: PIT:PIT 0 Timer at 22095.9628 Hz mode 3
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978110385: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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2) The demo animations and music will play at 1/2 speed
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Again, DOSBox debug messages will show:
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353328489: PIT:PIT 0 Timer at 284.0233 Hz mode 3
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355019387: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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355022154: PIT:PIT 0 Timer at 277.4197 Hz mode 3
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356752840: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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356752840: PIT:PIT 0 Timer at 284.0233 Hz mode 3
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358443738: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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358446505: PIT:PIT 0 Timer at 277.4197 Hz mode 3
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3) The demo will actually run at normal speed
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Again, DOSBox debug messages will show:
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98621248: PIT:PIT 0 Timer at 527.4898 Hz mode 3
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99683536: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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99771158: PIT:PIT 0 Timer at 551.8881 Hz mode 3
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100788381: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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101290855: PIT:PIT 0 Timer at 527.4898 Hz mode 3
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102353108: PIT:PIT 0 Timer at 18.2065 Hz mode 3
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102440734: PIT:PIT 0 Timer at 551.8881 Hz mode 3
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For some scenes, the demo will converge on 421Hz,
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and for other scenes, will rapidly alternate
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between 527.48Hz and 551.881Hz.
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It is possible at any time, if timing bugs happen
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to line up, for the demo to run normally, then suddenly
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lose control of the timer and slow to a crawl or
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stop.
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Also noteworthy is that compiling DOSBox in debug
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mode (C_DEBUG) increases the chances of the demo
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running normally. Non-debug builds are much more
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likely to fall into the 1/2-speed situation.
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- VGA mode-change glitches.
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I also noticed that the music will audibly skip or
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miss a beat when one scene transitions to another and
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a mode change is involved.
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