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From: John Capo <jc@irbs.com>
Message-Id: <199507132237.SAA16948@irbs.irbs.com>
Subject: Re: How to enable/disable hardware compression with HP DAT
To: roberto@keltia.freenix.fr
Date: Thu, 13 Jul 1995 18:37:34 -0400 (EDT)
Cc: freebsd-hackers@freefall.cdrom.com (freebsd-hackers)
In-Reply-To: <199507132044.WAA00350@keltia.frmug.fr.net> from "Ollivier Robert" at Jul 13, 95 10:44:14 pm
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Ollivier Robert writes:
> 
> Hello anyone (especially Julian and Peter),
> 
> I just got a   new DAT from  HP  (SureTape  5000,  SCSI-2, DDS  and  DDS-DC
> compatible)  and I'd like to  know how to enable   and disable the hardware
> compression  by software. I   guess there is a  couple  "scsi -c something"
> which do the job but I don't know SCSI enough...
> 
> ahb0: reading board settings, int=11
> ahb0 at 0x5000-0x50ff irq 11 on eisa slot 5
> (ahb0:4:0): "TANDBERG  TDC 3600 -07:" type 1 removable SCSI 1
> st1(ahb0:4:0): Sequential-Access st1: Tandberg tdc3600 is a known rogue
> density code 0x10,  drive empty
> (ahb0:5:0): "HP HP35480A 1009" type 1 removable SCSI 2
> st0(ahb0:5:0): Sequential-Access density code 0x13, variable blocks, write-enabled
> 

It will be eaisest to disable compression via the option switches.
The compression is controlled by mode select page 0x0F according
to the docs I have for a HPC1553A which is a drive with an autoloader
that holds 6 tapes. Byte 2, bit 7 controls compression. Byte 3,
bit 7 controls decompression.  A vaule of 1 enables, 0 disables.

John Capo