Fair arbitration on new parallel interfaces?

Lohmeyer, John JLOHMEYE at cossymwest.co.symbios.com
Tue Sep 17 10:14:00 PDT 1996


* From the SCSI Reflector (scsi at symbios.com), posted by:
* "Lohmeyer, John" <JLOHMEYE at COSSYMWEST.CO.SYMBIOS.COM>
*

Jeff Blaalid wrote:
 ----------
>    Is there any work on migrating to a Fair Arbitration that is
>    compatible with the current priority based arbitration?

Jeff,

Yes.  A very old IBM proposal (circa 1990) documents how to do fair   
arbitration on SCSI without violating any existing rules.  The SCSI   
Working Group has recently reviewed this proposal and recommended that it   
be included in SPI-2.  Of course, it needs some significant editorial   
work.  The proposal was recently given a current X3T10 document number   
(96-172) and was included in the May X3T10 mailing.  (See 96-172r0.doz   
(ZIP'd Word file) on the SCSI BBS (719-533-7950) or in the   
/pub/standards/io/x3t10/document.96 directory on ftp.symbios.com.)

In a nutshell, the fairness algorithm works by voluntary refraining from   
arbitration.  If a device wins arbitration, it notes which lower-priority   
devices lost arbitration.  Then the device refrains from arbitrating   
again until all lower-priority devices which lost arbitration have won a   
cycle.

John

 --
John Lohmeyer                 E-Mail: john.lohmeyer at symbios.com
Symbios Logic Inc.             Voice: 719-533-7560
4420 ArrowsWest Dr.              Fax: 719-533-7036
Colo Spgs, CO 80907-3444    SCSI BBS: 719-533-7950 300--14400 baud



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