Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

SCSI Self-Selection

IP.com Disclosure Number: IPCOM000119818D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 102K

Publishing Venue

IBM

Related People

Bakke, BE: AUTHOR [+4]

Abstract

A method for suspending SCSI bus activity to perform concurrent maintenance is disclosed. The suspension does not parasitically affect devices on the bus.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

SCSI Self-Selection

      A method for suspending SCSI bus activity to perform
concurrent maintenance is disclosed.  The suspension does not
parasitically affect devices on the bus.

      FEATURES:
   Allows control of the SCSI bus to be obtained in real time for
purposes of concurrent maintenance.
   Easy for microcode to enable.
-  Programmable external interrupt indicating completion.
-  Mechanism to obtain higher test coverage during BATs (Basic
Assurance Tests).
   Does not parasitically affect outstanding operations.
-  No microcode/hardware interface timing dependencies.

      Asynchronous requests to perform concurrent maintenance
requires the SCSI controller to obtain bus ownership in real time.
The mechanism to suspend SCSI bus activity in real time has to
conform to SCSI bus architecture.  Simply stated, the initiator has
to capture and control the bus while still conforming to the SCSI
architecture.  SCSI architecture requires the initiator to obtain
control by selection while devices obtain control through
reselection.  Both cases involve an initiator and target.  Due to the
peer-to-peer nature of SCSI architecture, this would require
microcode to terminate all outstanding device operations and remove
all queued operations in the initiator.  After all outstanding device
and initiator operations were aborted and cleared, the microcode
could service the request for concurrent maintenance.  Microcode then
would have to recover all aborted device operations and recover all
queued operations to continue normal system processing.  Previous
attempts to solve the concurrent maintenance problem have all have
unacceptable limitations (see the table in Fig.  1).

      This invention describes an alternative, SCSI Self-Selection,
that avoids limitation of the other methods. With SCSI Self-Selection
microcode simply enables SCSI Self-Selection and services the request
for concurrent maintenance.  Concurrent maintenance operations become
non-parasitic to devices on the SCSI bus and can be overlapped with
pending device oper...