debugging a kernel that doesn't start

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I'm trying to run NetBSD on a Dell PowerEdge R6515, and the kernel is being 
loaded (PXE or USB) but then the machine hangs hard.

What's the way to debug a kernel that hangs so early that you can't printf 
or drop into ddb? I guess that's a phenomenon quite common for a new port 
or changes to locore.s (or whatever that's called today), but it's completely 
new to me.

I have virtually no clue about PeCee hardware. At the point the kernel is 
started, are BIOS routines still available?