[5141] in linux-scsi channel archive
Re:Tekram DC-390 [OctoChecked] [OctoChecked]
daemon@ATHENA.MIT.EDU (fochlerj@dupont-photomasks.de)
Sun Nov 15 11:56:57 1998
From: fochlerj@dupont-photomasks.de
To: linux-scsi@vger.rutgers.edu, rjohanne@piper.hamline.edu
Date: Sun, 15 Nov 1998 17:08:16 +0200
Jörg Fochler@DPI
15.11.98 17:08
>I've the above card which has two internal connectors, one wide and the other
narrow.
>consequently have two drives, one wide and one narrow,
>which I'm trying to run off of the two connectors. I have a wide cable
>for the wide drive, and a narrow cable for the narrow drive.
>
>The problems is that when I connect both drives to the respective connectors,
the
>scsi-controller bios does not detect any of them, and proceeds on to say, for
each id
>(0-15), "unexpected disconnect: try to disable wide negotiation or sync
negotiation for
>this device"
>
>I've tried disabling that as the message says, but with no success. What am I
doing
>wrong?
>
>Much help will be appreciated
>
>Thanks
>
>robert
>
I don't know exact this adaptor, but all other hostadaptors i've seen with
narrow &
wide connectors have only ONE physical SCSI bus. The "wide" part is made with
all
lines whilst the "narrow" part is merely the lower eight bits and the neccessary
control signals, grounding, termination power.
Because it's only a single bus system, you have to be sure about following:
a) Use different SCSI id's for every device connected, no matter to wich
cable
the connection is made
b) Termination is needed on both _physical_ ends of the lines.
This means in your case you have to terminate the narrow cable as well
as
the wide cable AND on the hostadaptor the upper 8 bit of the bus.
On some boards you can select the termination of the bus between none,
upper part and wide (16bit). In your above given constellation you need
the
second choice.
For best results use _active_ terminators. Even if modern SCSI devices
provide
so called "active" termination, better use external active terminators
and
disable the device terminators.
Again: Use the _last_ physical connector (counted with view from
hostadaptor)
of the respective cable for termination. That's also valid, if you
decide
not to use external termination. Then an active terminated device
should be
attached to the last connector.
General rule: No open ends of any SCSI cable.
c) Don't rely on autoterm ! Better switch on/off the neccessary
termination
in the adaptor settings by yourself.
d) If there is still a problem with wide negotiation, try to disable it for
all
related devices.
Next step: Try to slow down the bus speed and/or exchange the SCSI
cabels
(you use good quality cable, not longer than specified, don't you ??
;-)
If this is not successful it may be, that you have a broken device or at
least a device with faulty firmware (e.g. some Quantum drives were
famous
for that :-( ). Last chance could be then to use the kernel SCSI
support
without any specialities like command queueing,
BTW: Never use all three connectors of a hostadaptor if it's not explicitly
allowed.
You would construct a "T" cabelling which would lead to a nonconformant "bus".
For the newest hostadaptors it is allowed, because of a SCSI bridge chip for the
wide
part which separates the wide and the narrow part _physically_ but not logical
(this
chip also provides the U2W part with LVD signals).
Another thing for general interest: In the last few weeks i've seen that the
newest
SCSI devices apperently don't have any kind of termination "on board" anymore.
Seems, the manufacturers rely more and more on external termination too.
Hopefully this will give them the chance to reduce the selling prices of the
drives
which are much too high related to EIDE drives (some cost less than half of SCSI
!)
Hope that all above will help you some way.
Best regards
Joerg
-
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@vger.rutgers.edu
