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New Channel Commands for Allowing Data Chaining of Variable Length Records

IP.com Disclosure Number: IPCOM000088071D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Opdahl, R: AUTHOR

Abstract

If an ending status is received from a control unit when Chained Data Address (CDA) commands are executing on an IBM System/370 channel, the channel command word (CCW) chain is broken because the CCW pointer in the channel hardware is not pointing at a new Command Chained command. The CCW string must be restarted by the input/output supervisor (IOS) program at the next Command Chained Channel Command Word which uses substantial central processing unit (CPU) time. It would be preferable to use one of the following two methods to avoid data stream termination and a new Start input/output (I/O) procedure.

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New Channel Commands for Allowing Data Chaining of Variable Length Records

If an ending status is received from a control unit when Chained Data Address (CDA) commands are executing on an IBM System/370 channel, the channel command word (CCW) chain is broken because the CCW pointer in the channel hardware is not pointing at a new Command Chained command. The CCW string must be restarted by the input/output supervisor (IOS) program at the next Command Chained Channel Command Word which uses substantial central processing unit (CPU) time. It would be preferable to use one of the following two methods to avoid data stream termination and a new Start input/output (I/O) procedure.

By defining a new channel command, Chained Data Address Read (CDARD), and installing the ordinary decoding logic in the control unit to recognize the CDARD command as the first command in a string of pseudo chained data commands for reading a block of data, suppress length incorrect (SLI) flags can be set in the CDARD command and following channel read commands (RD). The control unit, having recognized the CDARD command as the first command for reading a data block of unknown length, will treat each following RD command as a CDA command and will provide data from the same block until the entire block has been read, at which time the normal ending status of Channel End/Device End is presented by the control unit. The control unit continues to respond with normal ending status to each chained RD command and the...