Subject: Re: NCR Driver Problems
To: None <current-users@NetBSD.ORG>
From: Christoph Badura <>
List: current-users
Date: 01/23/1996 19:08:13
Gordon W. Ross writes:

> Using tagged commands on your SCSI bus eliminates the
> bus arbitration and selection phases between commands,
> and just keeps the SCSI bus busy, proceeding directly
> into the next comand phase.

I believe you mean linked commands not tagged commands.

> Furthermore, keeping the SCSI bus busy between commands
> is not necessarily desirable.  If you have reselecting
> targets, they will have to wait longer to "get in" and
> finish the commands you have already issued to them, so
> those jobs will take MUCH longer to finish.

I don't think so.  The target can disconnect after the command phase.
It's just that when the target reconnects it will enter a new command
phase immediately after the data in/out and status phases thus saving
an arbitration phase.

I notice that BusLogic has discontinued support for linked commands in
24-bit mode in the newer firmware.  I'm not sure what that means.

> I'm NOT saying "tagged commands are always bad" but
> they are not necessarily always better.

Actually, with tagged commands one can fire off a couple of commands
to a target.  Without tags one has to wait for each command to
complete before sending the next to the target.  This could improve
performance.  However, my question is has anyone actually seen it.
No, I don't trust the ncr driver.

Christoph Badura

You don't need to quote my .signature.  Everyone has seen it by now.
Besides, it doesn't add anything to the current thread.