Jason O'Broin Desktop-SP writes:
 > My SCSI card is id 7 and the CDROM is id 3, both of which seems 
 > reasonable.
 > The CD ROM is on the internal interface. There is nothing on the external
 > interface.

OK so far.

 > I've set termination on the Cumana adapter (done from software), but 
 > there
 > doesn't appear to be any termination on the Sony CDU-561 CD ROM drive
 > (its one that came out of an old MEU unit), and none of the jumpers at 
 > the
 > rear of the drive enable termination. 

I'm unfamiliar with this unit, but it's likely to be unterminated if
it was in the MEU.

 > I'm assuming that, as a result, there is no termination, and I've got a 
 > resistor
 > pack on order.

I think this is a fair assuption.

 > However, the CD-ROM works normally (under RISC OS), happily passes the
 > diag tests that Cumana's SCSIDiag program runs, and I can get as far as 
 > getting
 > the NETbsd kernel to load off it. What happens in the scsibus0 phase?

The scsibus is reset, and a TestUnitReady is sent to each possible
device. If a response occurs from a device then it is attached to the
appropriate driver. It sounds as if the drive is failing to respond to
the ModeSense (AFAICR) which is the next command sent if the
TestUnitReady succeeds.

My advice is to check the termination.

 > Jason

Cheers Scott

-- 
Scott Stevens, Network Services Group, Computer Centre, Imperial College
"Alllllriiiigghttiiieeee then"                              - Ace Ventura