I'm at a loss to explain this, as soon as npx gets probed, the system  
locks hard. If I disable it in userconf everything seems to work. The  
last lines on the display are:

PNP0C01 at acpi0 not configured
PNP0000 at acpi0 not configured
PNP0200 at acpi0 not configured
npx0 at acpi0 (PNP0C04)
npx0: io 0xf0-0xff irq 13


I can't build a kernel without npx because it fails to link:

cpu.o: In function ` cpu_hatch`:
cpu.c:(.text+0x6e7): undefined reference to `npxinit'
acpi_wakeup.o: In function `acpi_md_sleep':
acpi_wakeup.c:(.text+0x495): undefined reference to `npxinit'

This is a hard lockup, caps lock and num lock don't work, nor the  
three fingered salute, nor the power button. so I built the same  
kernel with npx at isa, it doesn't print that it takes an irq, but it  
seems to work. So as to why the acpi npx probe is failing and the isa  
one is succeeding, I don't know.

Also, when booting with npx disabled in userconf, I later see

...
ioapic0: enabling
WARNING: Callback scheduled before sysmon task queue thread present.