Browse Prior Art Database

Dynamically Maintained Command Chains

IP.com Disclosure Number: IPCOM000049226D
Original Publication Date: 1982-May-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Nolta, AH: AUTHOR [+4]

Abstract

It is common practice when dealing with peripheral equipment to chain a series of commands such that closely related operations can be efficiently performed. Such command chains occur between a host and a peripheral device as well as between certain control units and peripheral devices. During data movements and device disconnected operations (seek, set sector, rewind tape, etc.) between either the control unit and the peripheral device or between the host and the peripheral device, the controlling unit (host or control unit) monitors for additional requests for the then selected peripheral device. The requests are sorted into queues for efficient peripheral operations and placed in a work table. When the last command of the chain of commands is being executed, the work table is examined.

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Dynamically Maintained Command Chains

It is common practice when dealing with peripheral equipment to chain a series of commands such that closely related operations can be efficiently performed. Such command chains occur between a host and a peripheral device as well as between certain control units and peripheral devices. During data movements and device disconnected operations (seek, set sector, rewind tape, etc.) between either the control unit and the peripheral device or between the host and the peripheral device, the controlling unit (host or control unit) monitors for additional requests for the then selected peripheral device. The requests are sorted into queues for efficient peripheral operations and placed in a work table. When the last command of the chain of commands is being executed, the work table is examined. If requests can be efficiently performed by the then selected device, the requests are made into a secondary chain of command and tacked onto the original chain of command. Then upon completion of the last command, the tacked chain of commands is executed as if a part of the original chain. Chaining can be concatenated through a plurality of operations subject to timeout and other load-balancing controls. Upon completion of the last command, and the last tacked on chain, the device is deselected.

This article describes a peripheral storage system which receives commands and chains of commands (CCWs). Some of the CCWs are executed directly against the device by a series of device commands through a direct control. Others of the CCWs are directed to a buffer control which operates a buffer as a cache which is logically interposed between the direct-access storage device (DASD) and the host. The buffer control, in satisfying user requests, instructs chains of internal commands (ICWs) which are supplied to the direct control in the manner identical to the CCWs such that the direct control can operate either with the host or with the buffer control in a substantially identical manner. For accessing DASD, the buffer control queues the received CCW commands in a CCW work table. The buffer control sorts the commands by device in a plural device peripheral storage system.

Based upon predetermined algorit...