Driver test failed: APIC seems to fail

[DB]

I've installed Mach3 on my P4 XP system. I did a clean install, removed all junk (but did install all drivers off course), disabled power management in any way I could (including in the BIOS), so I thought: Mach3 should run flawlessly now. but it doesn't. When I run the drivertest, at first glance it seems to be working perfect, a clean line, 24700 pulses/second or so, but after 1 or 2 seconds the pulses/sec goes down to 96 and it doesn't go up again. when I choose a different kernel speed it goed back up, stays there for 1 or 2 seconds, and goes down again.
what I've tried so far:
- install the special driver (no difference)
- installed an older version of mach (no difference)
- tested every LPT port setting available in BIOS (no effect)

if I recall correctily, the best port setting for mach3 is EPP with interrupt.
one thing I did notice however is that in the drivertest,  the APIC timing constant is always 0, and so is the box 'interrupt used'. it seems to me that that isn't good.

does anyone have any idea how to get this working?

[AndrewM]

Have you tried the XP Optimization file?

http://www.machsupport.com/downloads/XP_Optimization.txt

[DB]

yes, I have. actually, I did even more than that, since I also disabled power management in BIOS. but I don't think optimization is the problem, these optimizations are for keeping as much procesor time as possible free for Mach3, so this timing line is as stable as possible. during the first 2 seconds this line is very stable, but then my pulses/sec goes down.
so far, the two things I've noticed which I think aren't normal: when I start the drivertest, the line seems perfect, 24500 pulses/sec, but the score bar says pulsing too fast. second: apic timing constant is 0.

[DB]

It's working! the problem was indeed with the interrupt: the parallel port was set to use interrupt 7. it was set this way in the bios, and in the device manager the parallel port was set to use an interrupt. but, windows still didn't get it: on the resources page in device manager, there wasn't any interrupt mapped to the parallel port. so, I mapped IRQ7, et voila, the steppers are stepping!

the system is very stable now, the line almost completely flat. even 100KHz is no problem. one funny thing: APIC timing constant is still 0.