> 
> But why? the shac and sgec are connected directly to the DAL lines, 
> and essentially act as nexus devices! configure them as such!
> 
> mainbus0
> cpu0 at mainbus0 
> uba0 at mainbus0 (if theres a Q or unibus) 
> sgec0 at mainbus0
> shac0 at mainbus0
> etc etc
> 
> why create an added layer just to make the embedded nexi look like
> ordinary bus-conected devices? the nexus is a really cool construct! 
> 
Because mainbus should only be used as a "top-level bus holder" for
the different machine types. Therefore it is already splitted like:

sbi*	at mainbus0	# 780, 8600
cmi*	at mainbus0	# 750
bi*	at mainbus0	# 8200
vsbus0	at mainbus0	# 2000, 3100, 4000/x0
mvbus0	at mainbus0	# MV2, MV3, 3[3-9]00, 4000/x00

The here given bus is actually the main bus in the specific architecture.
"Nexus" in the old config system were used as the "master bus" but the
same for all architectures, which made the structure a little bit 
chaotic in the code.

-- Ragge