The probeget routine starts as follows:

	set	KERNBASE, %o2
	cmp	%o0, %o2		! if addr < KERNBASE
	blu	Lfsbadaddr		!	go return error

What is the point of comparing against KERNBASE?

The problem is: on a Sun-4, zs1 lives at obio address 0, and probeget
doesn't seem to find anything at address 0.  As a result, the keyboard
downlink is not found, and the kernel panics when /dev/kbd tries to open
the non-existent zs1 tty.

Now, I don't have my Sparc manual around, so I'm not sure if I'm reading
this code right, but it does have me confused.  KERNBASE is 0xf8000000
and I have devices both below and above it (VME/non-VME) and aside from
zs1 at 0, everything else is found.