[9fans] 9fs and 1542

[forsyth@caldo.demon.co.uk forsyth@caldo.demon.co.uk]

>>1. When the PC is configured as a plan9 terminal,
>>   it shows no problem in booting and can read/write
>>   the scsi disks without problem.

with the CDROM version of the system,
the cpu server/terminal use of scsi is more restricted
than the file server's: it won't operate on several devices simultaneously,
for instance (similarly for the adaptec diagnostics).
that alone might hide some underlying
problems with your configuration that do show up when you
use the file server's drivers.

>>I have believed that I can make the card terminated
>>only by setting dip-switch #1 on the card.

we emphasise checking termination because it is a common error to
leave termination on at several or all devices or conversely have it on none.
that can cause intermittent hangs,
devices to be unreliable especially at higher speeds or when working
in parallel, and other peculiar problems.

the scsi chain must be terminated at each end,
and only at each end.

there is often an internal connector and an external connector
on the host controller.  the host controller is then logically in
the middle.  i'd need 1542cf documentation (which i have got but can't find),
but i'd suspect that the switch selects termination at the card:
if the switch is set to terminate, either the internal
or external connector must be unused.
some host controllers can sense whether something
is connected, and supply or remove termination automatically
as required.  if the controller doesn't do that, and the switch
doesn't behave as i've guessed, you might need to put a
scsi terminator on the external connector if you're not using it.

on the internal scsi devices, as you follow the cable
out from the card, you must ensure that every device but
the last is NOT terminated and the last IS terminated.
unfortunately, the details of setting termination vary,
especially with older devices:
some devices require you to add or remove one or more
terminating resistor packs,
on others you must set jumpers accordingly,
and a few i've seen require both.
it's the same principle for the daisy-chained external scsi chain,
except that it's usually more convenient to remove termination
from all devices, and plug a terminator into the last connector
in the chain.

having sorted out the basics of termination,
there is the matter of termination power (should the device
provide termination power to the bus, etc),
does the device do synchronous i/o correctly,
disconnect/reconnect, and so on.
i'd check the termination first, though.