Browse Prior Art Database

Automatic Small Computer System Interface Rate Limiting

IP.com Disclosure Number: IPCOM000118779D
Original Publication Date: 1997-Jul-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Galella, JW: AUTHOR [+4]

Abstract

Disclosed is a method for automatically limiting the Small Computer Systems Interface (SCSI) Synchronous Data Transfer Rate as a function of cable connections. If external cables are in use, the SCSI synchronous rate is restricted.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Automatic Small Computer System Interface Rate Limiting

      Disclosed is a method for automatically limiting the Small
Computer Systems Interface (SCSI) Synchronous Data Transfer Rate as a
function of cable connections.  If external cables are in use, the
SCSI synchronous rate is restricted.

      This invention limits the maximum SCSI Synchronous Data
Transfer Rate (SDTR) for a shared SCSI bus between internal and
external adapter connectors.  The SDTR can be set to a maximum rate
or a predetermined slower rate.  The SDTR is determined by the
detection of an external cable attachment.  If external cables are
present, then the SDTR is set to a lower predetermined rate.  The
SCSI adapter checks the cabling status prior to the initial SDTR
negotiation and, thereafter, anytime the adapter needs to renegotiate
SDTR.  Some situations under which renegotiations will occur include:
  o  if an error has resulted due to an improper cabling environment
  o  if newly-attached devices are being configured
  o  if previously attached devices are being reconfigured

      Whenever the adapter checks the cabling status and detects a
change, the adapter will renegotiate with all devices.  If the
external cable is present, the adapter software will force a new SDTR
for all devices at the lower rate.  Conversely, if no external cables
are present, the adapter software will force a new SDTR for all
devices at  the maximum SCSI rate.