Browse Prior Art Database

Decode for DASD Attachment

IP.com Disclosure Number: IPCOM000050604D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Tutt, WE: AUTHOR

Abstract

A method and apparatus is described for decoding an operation or command register for a hardware disk attachment which allows ultimate flexibility in combining ID time and Data time functions for any particular sector.

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This is the abbreviated version, containing approximately 68% of the total text.

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Decode for DASD Attachment

A method and apparatus is described for decoding an operation or command register for a hardware disk attachment which allows ultimate flexibility in combining ID time and Data time functions for any particular sector.

On most direct-access storage devices (DASDs), each sector is comprised of an ID field and a data field. For both fields, it is desirable to have an attachment which can perform the following four operations: (1) Idle (do nothing), (2) Read (from disk into storage), (3) Write (from storage to disk), and (4) Compare (compare storage with disk). Each of these four operations may be thought of as stimulating storage and the DASD according to Table I, where + means to the storage or DASD and 1 means from the storage or DASD.

TABLE I Stimulus Data Flow Operation Storage DASD Storage DASD IDLE WRITE WRITE -> -> READ WRITE READ -> -> WRITE READ WRITE <- <- COMPARE READ READ <- <- Note that Idle is a no-op operation, and, since no data exists, Idle causes no writing to storage or DASD.

The method herein utilizes a command register of which four bits are used to define the storage and DASD data flow directions and consequently the desired operation. Two bits define the desired operation during the ID portion of the sector, while the other two bits define the operation for the Data portion. Operations decode switching is done in the transition portion between the sector's ID and Data fields. In this way ID time functions and Data time functions may in one command be combined to define usable operations on any sector of the DASD.

Commands which are usable from a system standpoint are defined in
Table II below. TABLE II

Command ID Time Oper. Data Time Oper.

IDLE IDLE IDLE READ ID READ IDLE READ RECOVERY IDLE READ WRITE ID WRITE WRITE READ SECTOR COMPARE READ WRITE SECTOR COMPARE WRITE SCAN SECTOR COMPARE COMPARE READ ID/VERIFY DATA READ COMPARE If an attachment has an 8-bit command register, four bits may be used to define the command. The four bits of the command register required to accomplish these functions are defined bel...