> A quick guess would be that XFree is setting a region that overlaps
 > the 2940's register space as allowing write combining. You should
 > be able to determine if this is a problem by looking at the XFree86
 > logs and correlating its actions with the register window for the
 > 2940.

According to AHC_DEBUG, the 2940 is mapping itself into 0xe273f000-
0xe274a000. Both XFree3 & 4 have the video and register memory
aperatures mapped to the same base addresses (0xe6000000,
0xe5000000). The system resource map says something is taking up
0xe0000000-0xe3ffffff, but doesn't say what.

 > You could also force the 2940 to use PIO, but I'm not sure how
 > you'd do this in NetBSD.

I have tried removing "AHC_ALLOW_MEMIO", to no effect.

I have finally managed to trace the hang to inside the call of
xf86ExecX86int10(pInt) in
xsrc/xfree/xc/programs/Xserver/hw/xfree86/os-support/vbe/vbe.c
...So, the problem's occuring in a real-mode BIOS call. Eek.

-- 
Chris Baird,, <abuse@brushtail.apana.org.au>