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Maes

Doom and Doom2.exe under DOSBOX

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OK, I'll admit there's little reason to use the original version with no mouselook, low resolution software renderer (ah, LOW DETAIL mode was my best friend back in the 486, 4 MB and inefficient BSP days ;-) ) and several engine limitations, other than testing the original gameplay.

However, while DOSBOX seems to manage the sound libraries just fine, it causes that strange phenomenon: on a *REAL* 486 machine, you could expect something between 16 and 25 fps with frame skipping (that is, the screen became jerky to keep up with gameplay speed), while DOSBOX outputs something between 16 and 25 fps on a 3 GHz machine, only WITHOUT the frame skipping! In other words, it's like playing Doom smoothly but in slow-motion by a factor of 2-3 !

Probably the initial CPU speed test doesn't take into account DOSBOX's limited video output speed, and thinks you have a super-fast CPU without adjusting the frame skipping automatically! Any workarounds?

Edit: it seems that the frame skipping works correctly sometimes, other times it doesn't.

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Its not playing in slowmo it just needs more CPU cycles.

EDIT: if I run doom in DOSBox I use 25000 cycles for smooth play at proper speed.

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HobbsTiger1 said:

Its not playing in slowmo it just needs more CPU cycles.

EDIT: if I run doom in DOSBox I use 25000 cycles for smooth play at proper speed.


This must have something to do with the maximum frame rate achievable by DOS Doom, which must be 70 fps.

The initial CPU speed check, on my machine at least, probably is fooled into thinking that the emulated machine has the power of firing off 70 fps (which this is clearly not the case) and sets the slowdown accordingly.

As I said in the last edit (in italics), sometimes it properly activates frame skipping (and then increasing CPU cycles DOES help), and sometimes it doesn't (in which case, increasing CPU cycles just increases the frame output by a small factor, but if you get 16-25 "smooth" fps, you would need to increase CPU cycles by a factor of 3 to 5, at least.

This is probably caused by DOSBOX's unusual performance difference in emulated CPU cycles (which even includes dynamic compilation, and probably fools doom into thinking it can output 70 fps) and emulated VGA output (which clearly cannot keep up).

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HobbsTiger1 said:
Its not playing in slowmo it just needs more CPU cycles.

EDIT: if I run doom in DOSBox I use 25000 cycles for smooth play at proper speed.


OK tried that too, I even tried different emulation cores (small, normal, full, dynamic) but still I couldn't get consistent results.

I started DOOM2.exe with the -devparm parameter to bring up that old iD frame counter (the less dots you see, the smoother it runs, exact formula was something like FPS= 70/(NOfDots+1) and sometimes increasing the CPU cycles in-game[i] helped (game speed stayed the same while FPS count smoothness increased) while other times it [i]increased just the emulated FPS output, and the game appeared to run in a smooth slow motion, and increasing the CPU cycles further just made the sound break up...really weird.

Sometimes it worked as intended, others times not.

Then I was enlighted: starting DOSBOX with more CPU cycles instead of increasing them in-game solved the problem. With about 14000-16000 cycles it feels much like an 486 DX/50 o;-)

For a REALLY overkill experience try setting the memory to 4 or 8 MB ;-)

I personally completed both DOOM and DOOM2 on UV with just 4 MB (later upgraded to 8), while almost no other DOOM-like game of the time even started with 4 MB :-)

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I set the cycles to auto (see the .ini or .cfg whatever it is) and all of my DOS FPSs work fine, maybe a little laggier than 36fps but definitely at least 20.

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