Browse Prior Art Database

Extension to Command Retry

IP.com Disclosure Number: IPCOM000081199D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Dugan, RJ: AUTHOR

Abstract

This apparatus eliminates the requirement that control units send an interrupt to the central processor, indicating that they are no longer "busy". The command retry function described in U. S. Patent 3,688,274, Cormier et al., is utilized to accomplish this. In that patent there is described a data channel, in which a control word containing a command is retained in a backup register. Upon the occurrence of a signal from an attached control unit, a retry of the retained command is accomplished without interrupting the computer to retry the original, initializing command, even though intervening control words were executed.

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Extension to Command Retry

This apparatus eliminates the requirement that control units send an interrupt to the central processor, indicating that they are no longer "busy". The command retry function described in U. S. Patent 3,688,274, Cormier et al., is utilized to accomplish this. In that patent there is described a data channel, in which a control word containing a command is retained in a backup register. Upon the occurrence of a signal from an attached control unit, a retry of the retained command is accomplished without interrupting the computer to retry the original, initializing command, even though intervening control words were executed.

Presently, when a control unit in an IBM System/370 computer is busy to a start I/O instruction, the channel returns a condition code of one with the busy bit set in the channel status word. The channel program then awaits the return of an interrupt from the channel before trying to start the I/O instruction again. With the modification described herein, for short busy intervals, a control unit indicates command retry status (without device end) as the initial status to a start I/O instruction. In this situation, the condition code returned is zero and the start I/O will not be queued to await an interrupt. When the control unit is no longer busy, the device end is sent to the channel to signal that the control unit is now ready for retry. The channel then reissues the retained command without submitting an interrupt...