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Browse Prior Art Database

Logical Control Unit

IP.com Disclosure Number: IPCOM000050342D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Anderson, DW: AUTHOR [+5]

Abstract

A "logical control unit" (LCU), as presently contemplated is a collection of stored information and associated firmware or the equivalent for enabling an I/O channel processing subsystem of a data processing system to control the initiation of I/O activities and to select specific channel interfaces and control units for such activities. Each LCU is associated with a unique maximal set of (physical) control unit elements which offer alternative paths of access to (physical) device elements. For example, if a device A is accessible through control units 1 and 2, a device B through control units 2 and 3, and a device C through control units 3 and 4- and if control units 1-4 do not offer alternative paths of device access relative to any other control units- then control units 1-4 constitute a set associated uniquely with an LCU.

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Logical Control Unit

A "logical control unit" (LCU), as presently contemplated is a collection of stored information and associated firmware or the equivalent for enabling an I/O channel processing subsystem of a data processing system to control the initiation of I/O activities and to select specific channel interfaces and control units for such activities. Each LCU is associated with a unique maximal set of (physical) control unit elements which offer alternative paths of access to (physical) device elements. For example, if a device A is accessible through control units 1 and 2, a device B through control units 2 and 3, and a device C through control units 3 and 4- and if control units 1-4 do not offer alternative paths of device access relative to any other control units- then control units 1-4 constitute a set associated uniquely with an LCU.

A system, as presently contemplated, also contains logical subchannels- one for each device potentially accessible to the I/O channel processing subsystem- which in effect are storage entities for retaining control parameters for controlling activities relative to the associated devices.

In such systems, requests for I/O initiative relative to a device are posted by central processing elements in the associated logical subchannel and the logical subchannel is linked into a threaded "primary" work queue serviced by the I/O processing subsystem. That subsystem is responsible for processing such enqueued requests on a FIFO (first in, first out) basis.

For each request the subsystem determines on a "logical" basis if the requested activity is subject to immediate initiation (i.e., if the associated sub...