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Multi-Processor System with Method for Releasing Allegiance of Device to Failing Processor Using Channel Commands Words to Detect Hung Device by Count of Successful Device Starts

IP.com Disclosure Number: IPCOM000105281D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Meritt, AS: AUTHOR [+2]

Abstract

A device controller keeps a counter for each attached device and increments the counter on each successful selection operation of the type that could be performed by a processor to which the device has allegiance. The counter is not incremented by selection operations that are not successful or by selection operations that could be performed on a reserved device by a processor that does not have allegiance to the device. For example, the counter would be incremented by the successful execution of the instruction Start Subchannel (SSCH) and it is not incremented by the instruction Sense Path Group ID (SNID). In normal operation, the counter for each device is incremented rapidly, but while the device has allegiance to a processor that has failed, the count remains unchanged.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Multi-Processor System with Method for Releasing Allegiance of Device to Failing Processor Using Channel Commands Words to Detect Hung Device by Count of Successful Device Starts

      A device controller keeps a counter for each attached device
and increments the counter on each successful selection operation of
the type that could be performed by a processor to which the device
has allegiance.  The counter is not incremented by selection
operations that are not successful or by selection operations that
could be performed on a reserved device by a processor that does not
have allegiance to the device.  For example, the counter would be
incremented by the successful execution of the instruction Start
Subchannel (SSCH) and it is not incremented by the instruction Sense
Path Group ID (SNID).  In normal operation, the counter for each
device is incremented rapidly, but while the device has allegiance to
a processor that has failed, the count remains unchanged.  This
counter is implemented as a field in a control block that can be
accessed by any processor using the instruction SNID.  A suitable
time after a processor has read the counter of a device that may be
hung by allegiance to a failed processor, it executes a CCW called
Release Allegiance with ID (RAID) which identifies the device and
supplies the previously read count that the device may be hung at.
In the execution of this CCW, the control unit compares the count in
the CCW with the count for the device.  If the counter has been
incremented in the meanwhile, the counts are unequal, and the control
unit returns a status byte that signifies that the device has been
operating normally or that it has already been released from
allegiance to a failed processor.  If the counts are equ...