Date: Tue, 4 Nov 1997 13:01:40 -0500 (EST) From: Neil Ludban <n-ludban@onu.edu> To: freebsd-hackers@freebsd.org Subject: How to limit SCSI speed? Message-ID: <Pine.A32.3.96.971104121914.16995A-100000@austin.onu.edu>
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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
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