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First post, by windi

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Hello

First I want to cheer for the latest release 0.70. I was able to get 80 000 cycles out of my main Athlon XP2400+ host, the dynamic core really has had some major improvements. It was enough to have enjoyable IPX multiplayer games in Doom and Heretic over the Internet finally. (yes, those games are nice in dosbox because the unix/win32 source ports of those games are always more or less screwed up when it comes to the game dynamics.)

However I have an odd problem on my Laptop. It's a Compaq Presario 900 with ATI radeon and Mobile XP1800+. Whenever I run certain games in dosbox, they work fine at first but after about 10 seconds the keyboard controls begin to lag horribly.. when you press and release a key, it has a lag of several seconds and it seems to change randomly. When you exit and enter the game again, it's the same thing over again. Fine at first, then suddenly begins to lag. I have tried with small cycles, max cycles, different frame skips and cores but it always happens. This doesn't happen in other SDL apps and games that I've tried. Also using different output= methods made no difference to the problem.

Have you ever experienced anything like this and do you have any ideas how to fix it?

At first I thought it might have something to do with the frequency scaling (Power Now, AMD's idea of Speed Step.) However even when I force it to max frequency all the time, the lag still happens.

Reply 1 of 4, by windi

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Update

I found out the cause already.. it's MPU401. Whenever it's enabled in the conf then games like Doom begin to have the keyboard lag. The funny thing is, it doesn't matter what midi-out device is used and it doesn't matter wether Doom actually uses General Midi, OPL or nothing. As long as dosbox has MPU401 disabled, everything's fine. As long as it's enabled Doom has keyboard lag even when it's configured to not to use any music device.

Reply 3 of 4, by windi

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After poking around the config file I found out the following combination for the laptop:
priority=normal,normal
cycles=max

It allowed to play Doom and similair games without any keyboard lag ever occurring while MPU emulation still enabled. However I found out that just by having the MPU enabled in the config and doom running with no music device it still has a big performance impact.. when looking to the timedemo statistics (doom's way of measuring performance):

doom2 -timedemo demo1
1205 gametics in 1689 realtics (mpu enabled and in use)
1205 gametics in 1497 realtics (mpu enabled, no music)
1205 gametics in 1475 realtics (mpu disabled, opl music)
1205 gametics in 1275 realtics (mpu disabled, no music)

Bigger realtics value means worse.

I don't think this is a bug though, it must be that playing and emulating music device is just this slow.. what I do wonder is that MPU enabled but not used still eats 222 realtics, that's 15% away, which in other words means that 15% of total performance is wasted by having a MPU running totally idle. Perhaps the MPU emulation code could be futher optimized in the future?

Reply 4 of 4, by windi

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By the way I have to cheer for dosbox again. We tried a 3 player Heretic deathmatch with dosbox ipx emulation over the internet, all 3 computers being rather low end (from Athlon XP1800+ to XP2400+ host CPU). It ran smoothly all time except a few slight slowdowns occuring randomly, which might have been caused by the Internet. 😁