Interesting problem with controller

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Hi all.

I have spent quite some time diagnosing this problem while attempting to break it down so apologies for the lengthy entry.  I know how difficult it can be to assist someone without the right information.

The problem is related to a PS2 keyboard hack.  I know most of you would likely recommend alternate options, but read on first please.

During the construction of a MAME arcade we used an older PC to test & configure different emulators and options.  Most of the time we used MAME32.  The input was an old IBM keyboard that was pulled apart, keys mapped onto a matrix to ensure no ghosting or blocking and for some weeks/months all was good, albeit slow on many ROMS due to older PC.

Nearing completion we decided that a faster PC was required.  So we secured a new(er) PC, put the same OS on it and copied the Emulator directly from the old PC to the new.

So in summary, although the PC itself was different, all the configurations in MAME32 (and other installed emulators/front end) was the same between old PC and new.

The problem was discovered in MAME32.  When starting any of the 1942 ROMS (loop master or 19xx etc - and there might be others), the input would freeze for almost a second or even two once the game started.  The freeze would not stop the frame-rate, although it did seem like there was a stutter in the sound at the same time.  The plane would simply ‘drift’ across the screen in the same direction you last pointed and you could not get it back until a second or two later.  The same would happen if you were holding down the fire button - it would stay on.  The same for all keys pushed by both player 1 and 2.  Then all was good for some time and then it happens again (say every 15-30 seconds or so).

We have proved that it is to do with the PS2 input, as we can use a USB keyboard (just to test) and there were no problems.  We can use the keyboard hack or a different PS2 keyboard and the problem comes back.

But…, here is the interesting thing.
We can go into Mortal Kombat, play for a little while, go back to any of the 1942 ROMS and all is fixed!  Not one problem! (yes - this could be a ‘work around’ - but I want to get to the bottom of this one if possible…)

We can repeat this problem every time.  Turn off arcade box, turn on, go to 1942 Loopmaster, have problem (happens within first 30 seconds or so), go to Mortal Combat and play for 30 seconds, go back to 1942 Loopmaster and all is good.  In fact, everthing seems to work from then on.  Shut it back off (or restart MAME32) and problem comes back.

Interestingly, if I change the video card driver from d3d to DirectDraw, the problem persists but is less noticeable.  I think this is because the PC is working less using DirectDraw and hence ‘gets over’ the problem quicker.

Any help or suggestions appreciated.

Thanks in advance.

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I know it is a difficult one, bit anyone got any suggestions at all?
Maybe some way to narrow the problem down a bit more?

Thanks in advance.