Browse Prior Art Database

Contingent Allegiance Enhanced Detection and Reset Function

IP.com Disclosure Number: IPCOM000046884D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Burt, DW: AUTHOR [+4]

Abstract

In IBM System/370 I/O operations, contingent allegiance is established by a control unit when the channel accepts from the control unit a status byte that contains unit check or contains attention that is detailed by sense information. A control unit will terminate a contingent connection when either: 1. An I/O operation is initiated down the path having the contingent allegiance. The exceptions are a Test I/O instruction or a No-Operation (No-op) command. 2. A general or selective reset on the interface owing the allegiance. Under normal circumstances, establishment of a contingent allegiance will have no effect on system operation. The operating system will issue a sense command to clear the contingent allegiance and obtain the sense information for recording and interrogation.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 56% of the total text.

Page 1 of 2

Contingent Allegiance Enhanced Detection and Reset Function

In IBM System/370 I/O operations, contingent allegiance is established by a control unit when the channel accepts from the control unit a status byte that contains unit check or contains attention that is detailed by sense information. A control unit will terminate a contingent connection when either: 1. An I/O operation is initiated down the path having the contingent allegiance. The exceptions are a Test

I/O instruction or a No-Operation (No-op) command. 2. A general or selective reset on the interface owing the allegiance. Under normal circumstances, establishment of a contingent allegiance will have no effect on system operation. The operating system will issue a sense command to clear the contingent allegiance and obtain the sense information for recording and interrogation. An exposure occurs when the following conditions are met: 1. Multiple CPUs sharing a DASD (direct-access storage device) through a single control unit. 2. A unit check is presented, a contingent connection is established, and any of the following additional

conditions exists:

a. The failure of the operating system to recognize a

unit check or take action when a unit check is

recognized.

b. A software malfunction (i.e., loop, wait state or

abnormal termination) that results in a

failure to issue the sense command.

c. The failure of a sense command to clear the

contingent connection caused by either: 1. A disabling hardware failure (CPU or channel that causes either the command to fail

to execute or not to be issued).

2. A power failure in the CPU.

3. The operator hitting stop on the CPU. The result of these conditions is that the sharing CPUs have lost access to all devices attached to the affected control unit. This will almost always result in an unscheduled Initial Program Load (IMPL) of the sharing CPUs. In the case of multiple control units, the problem will result in degraded performance due to the loss of one of the control units....