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Channel Interface Isolation for Recovery

IP.com Disclosure Number: IPCOM000049206D
Original Publication Date: 1982-May-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Moore, BB: AUTHOR [+4]

Abstract

System Control Programs (SCPs) can crash if a malfunctioning control unit or device generates a continuous series of I/O interruption conditions via a channel interface. This problem is known as a "hot I/O" condition. When recovery via a "halt-clear" device sequence, or channel reset, is ineffective, many central processor instruction cycles are wasted in processing (discarding) each of the interruptions. There many even be so much interference that system operations effectively cease until some adjustment is made. One adjustment would be to logically disable the problem channel via its channel mask bit. While this provides logical disablement to eliminate wasted central processor cycles, the channel processor which serves multiple interfaces may still expend cycles processing the "hot I/O" condition.

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Channel Interface Isolation for Recovery

System Control Programs (SCPs) can crash if a malfunctioning control unit or device generates a continuous series of I/O interruption conditions via a channel interface. This problem is known as a "hot I/O" condition. When recovery via a "halt-clear" device sequence, or channel reset, is ineffective, many central processor instruction cycles are wasted in processing (discarding) each of the interruptions. There many even be so much interference that system operations effectively cease until some adjustment is made. One adjustment would be to logically disable the problem channel via its channel mask bit. While this provides logical disablement to eliminate wasted central processor cycles, the channel processor which serves multiple interfaces may still expend cycles processing the "hot I/O" condition.

The following shows how an operator can electronically disable an interface, thus saving channel processor cycles: 1) The SCP detects that it is experiencing the hot I/O problem with channel interface n. 2) The SCP logically removes or disables channel interface n. 3) The SCP informs the operator that the hot I/O problem has rendered channel interface n inoperative. 4) The operator may choose to continue system operations without hannel interface n (if, for example, all devices attached to channel interface n are also attached to some other channel interface). He therefore enters the following command via a SCP console: VARY...