From owner-freebsd-hackers Tue Nov 4 10:02:16 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id KAA25215 for hackers-outgoing; Tue, 4 Nov 1997 10:02:16 -0800 (PST) (envelope-from owner-freebsd-hackers) Received: from postoffice.onu.edu (postoffice.onu.edu [140.228.10.2]) by hub.freebsd.org (8.8.7/8.8.7) with ESMTP id KAA25208 for ; Tue, 4 Nov 1997 10:02:13 -0800 (PST) (envelope-from n-ludban@onu.edu) Received: from austin.onu.edu (austin.onu.edu [140.228.10.1]) by postoffice.onu.edu (8.8.5/8.8.5) with SMTP id NAA25496 for ; Tue, 4 Nov 1997 13:01:38 -0500 (EST) Date: Tue, 4 Nov 1997 13:01:40 -0500 (EST) From: Neil Ludban To: freebsd-hackers@freebsd.org Subject: How to limit SCSI speed? Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@freebsd.org X-Loop: FreeBSD.org Precedence: bulk Hello, I tried adding an external SCSI Zip drive to my system and the kernel would no longer load (it would very slowly get a few sectors, then give up). Suspecting bad termination or cable lengths, I looked up the specs and found out that the cables are too long for my ultra-scsi2 hard drive. After changing the controller's BIOS to limit the disk to 5 or 10MB/s, the kernel loaded OK, but then FreeBSD (2.2.5) re-probed everything and failed to read the disk at full speed. It gave a couple pages of failed command errors, then hung. So, is there any way to set the maximum speed the driver will negotiate? The only thing I could find was SCSI_NCR_MAX_SYNC in the undocumented section of LINT (the controller uses the ncr 53c875j chip). Being able to configure the maximum speed at boot would probably be a good idea, for diagnostics and to accomodate extra cable lengths when temporarily adding external devices. In my case, the ultra drive was a good deal, but I don't need the extra bandwidth and don't want any of the trouble of configuring an ultra chain. --Neil