hello,
> 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


but the SBI adapter is a nexus device, just like shac and sgec are, 
for example! certainly sgec and shac are of far more limited scope of
operation than an SBI adapter is, but it _is_ connected as a nexus! 

> 
> 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.

im meaning nexus in the VAX sense, i.e. a device sharing in that innermost
of buses, to which a processor connects, bus adapters connect, and in later
machines, things like SGEC connect. Those are all nexi, and act with the
same powers as a VAX processor in the nexus. mainbus refers to the nexus
interconnect, and things like processors hang off of the nexus interconnect
and act as nexi. A VAX processor is a nexus device, as are SBIadaptors and 
SGEC and so on. 

i dont see why we should create another layer to put between nexi and 
anything. a SHAC is at the same level and the same privilege as the bus
adapetors. 

isildur