I've run into this same problem on two different machines now. I
compile a kernel with a config file that contains the following lines:

gus0    at isa? port 0x220 irq 7 drq 1         # Gravis Ultra Sound
audio*  at gus?

and when I install the gus card and boot, I am dropped into the kernel 
debugger at this point:

...
lpt0 at isa0 port 0x378-0x37b irq 7
gus0 at isa0 port 0x220-0x22f irq 7 drq 1
gus0: Gravis UltraSound, 1024KB memory
audio0 at gus0: full duplex
kernel: page fault trap, code=0
Stopped in  at  __isa_dmamem_alloc+0x4c:	movl	0x14(%ecx),%ecx
db>

The only strange thing I notice here besides the fact that I've been
dropped into the debugger, is that the audio0 line in the startup
messages says "full duplex", when in fact, according to the man page
for the gus driver, if no 'drq2' is specified in the kernel config
file the gus in this case should only be half-duplex as the same drq
is to be used for both recording and playback.

I tried installing this card in a different machine with very
different hardware, and compiling another kernel that supports the
gus, and ran into the exact same result. I also tried setting the gus
to different IRQ and drq in the kernel configuration file, and though
that worked, I was still dropped into the debugger at the exact same
point.

Is anyone out there successfully using a Gravis Ultrasound 'Classic'
(not the PnP, which works fine) with a NetBSD 1.4.1 kernel?  If not,
could the gus driver be broken in NetBSD 1.4.1?

Any help would be greatly appreciated. 

Thanks.

-Zach Fine
czyz@serv.net