Date: Mon, 24 Apr 95 20:41 CDT From: uhclem@nemesis.lonestar.org (Frank Durda IV) To: freebsd-hackers@freefall.cdrom.com Subject: Re: Interesting SCSI cdrom problem.. Message-ID: <m0s3ZdD-0004vvC@nemesis.lonestar.org>
next in thread | raw e-mail | index | archive | help
[1]From: Peter da Silva <peter@bonkers.taronga.com> [1]If there is a guaranteed unique ID you can get from the CDROM, you can [1]use that to maintain multiple mount structures in memory, and prompt the [1]user for the appropriate disc when necessary. [1] [1]If the prompt is vectored through a program (and it would pretty much have [1]to be), you could use that to control a jukebox as well. CDs have a field for the UPC data, which should be unique. However there are two problems (at least): 1. Not everybody fills in the field, including many big record companies. (Usually its because the UPC hasn't been assigned by the time the disc is mastered or they get in a hurry, it was dark, etc.) Write-once discs almost never have a valid UPC field and some of the mastering software doesn't even give you the chance to fill it in. 2. Not all CD-ROM drives (including SCSI models) implement a command that delivers the UPC field. That is probably why the CD-DA (audio) player app that Microsoft ships used to read the length information for each track from the TOC and create a hash from it. That was then used to "recognize" the disc being re-inserted so that it could recall preferences, tracks-to-skip, etc. This scheme is reasonably foolproof, providing the disc isn't remastered by a different vendor who gets the timing different on any track on the disc AND there isn't another disc that has the same number of tracks and length. Frank Durda IV <uhclem@nemesis.lonestar.org>|"Where do you want to go today? or uhclem%nemesis@fw.ast.com (Fastest Route)| Wherever Microsoft tells you ...letni!rwsys!nemesis!uhclem | to." - TM (C) 1994 Madsoft. ...decvax!fw.ast.com!nemesis!uhclem |
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?m0s3ZdD-0004vvC>