Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!know!samsung!usc!jarthur!uunet!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.periphs.scsi
Subject: Re: Standardized drivers... (was Re: NEC CDR-35 portable CDROM drive)
Message-ID: <13241@cbmvax.commodore.com>
Date: 16 Jul 90 21:11:13 GMT
References: <12215@shlump.nac.dec.com> <8575@goofy.Apple.COM> <12378@cbmvax.commodore.com> <1990Jun17.113043.20473@math.lsa.umich.edu>
Reply-To: jesup@cbmvax (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 31

In article <1990Jun17.113043.20473@math.lsa.umich.edu> hyc@math.lsa.umich.edu (Howard Chu) writes:
>In article <12378@cbmvax.commodore.com> jesup@cbmvax (Randell Jesup) writes:
>>	We already have this on the Amiga.  We have a protocol called
>>"scsidirect" which allows you to pass a control structure to the device
>>driver, which will then send your command (and optionally retrieve any
>>sense information).  The structure used looks like this:
>[copyrighted material omitted...]
>
>This seems like a lot of trouble to go to. The Atari ST has a lobotomized
>version of SCSI on the main board. Atari and a few other companies make
>host adapters that translate between Atari DMA and a full SCSI interface.

	It's not much trouble, it's only used for "unusual" uses of the SCSI
bus, where the programs needs real control.  Normal usage (read,write,format,
etc) go through the normal device-independant exec device interface.  Note
that SCSIDirect made is quite simple to write very user-friendly automated
setup programs that can work on any controller.  There are a couple different
ones, and they work interchangably.

	To deal with %&*# companies that don't correctly support SCSI we 
use a number of fall-backs in determining a reasonable geometry (while SCSI
is entirely block-based, our filesystems still want to partition on "cylinder"
boundaries).  The final fall-back if nothing else works is a read capacity
to find the size of the drive, and then another to find the first "slowdown"
on the drive (and assume that's the cylinder size).  Overall, this works
pretty well, and wastes few blocks, even on zone-recorded disks.

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.cbm.commodore.com  BIX: rjesup  
Common phrase heard at Amiga Devcon '89: "It's in there!"