[geeks] SUNW,xbox: SCSI?

[Mouse]

I've got a SUNW,xbox.  I recently found an expansion chassis for it.
Today, I got it all set up and plugged in.

It seems to work.  I have a SUNW,spif and a Magma 2+1 in the expansion
box; NetBSD says

xbox0 at sbus0 slot 2 offset 0x0 level 1 (ipl 2) level 2 (ipl 3) level 3 (ipl 5) level 4 (ipl 7) level 5 (ipl 9) level 6 (ipl 11) level 7 (ipl 13): model 501-1840
sbus1 at xbox0: clock = 25 MHz
spif0 at sbus1 slot 1 offset 0x0 level 13 level 7: rev 0x5/0x82 osc 1 (freq 9830400)
sptty0 at spif0: tty unit 0
sptty1 at spif0: tty unit 1
sptty2 at spif0: tty unit 2
sptty3 at spif0: tty unit 3
sptty4 at spif0: tty unit 4
sptty5 at spif0: tty unit 5
sptty6 at spif0: tty unit 6
sptty7 at spif0: tty unit 7
spbpp0 at spif0: bpp unit 0 (not implemented)
magma0 at sbus1 slot 2 offset 0x0 level 9 softpri 6: Magma LC 2+1 Sp
magma0: CD1400 0 addr 0xfe038000 rev 46 clock 25Mhz
mtty0 at magma0: 2 ttys
mbpp0 at magma0: 1 port

which is all very reassuring.

But the expansion box has two HD50 SCSI connectors on the back panel
and two 50-pin Berg SCSI connectors inside.  Looking at etch runs, I
would guess they are wired as a single SCSI bus.

But there is a notable lack of any SCSI interface in the above.  Using
ls in the OBP agrees: there is nothing but the two cards I put in the
expansion chassis beind the SUNW,xbox at 2,0.

So what's the deal with those SCSI connectors?  Are they completely
separate, being basically a two-disk disk enclosure in the same
pizza-box as (and sharing power and physical PCB but nothing else with)
the SBus expansion?  Or is the main host's SCSI bus extended somehow
(this would surprise me, as the 501-1840 connects directly to nothing
but the SBus and the expansion chassis)?  Or something else?

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