Browse Prior Art Database

Concurrent Sense Facility

IP.com Disclosure Number: IPCOM000120397D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 100K

Publishing Venue

IBM

Related People

Cormier, RL: AUTHOR [+9]

Abstract

Disclosed is the concurrent-sense facility, which allows the channel subsystem of ESA/390* systems to retrieve sense information from a device and present that sense information to the program along with the I/O interruption that contains the unit-check status indication. The facility described herein is the mechanism by which the sense information is retrieved from the device and the mechanism by which the sense information is actually returned to the program. Presenting the status and sense information together allows the program to realize a performance benefit because it no longer needs to perform a separate I/O operation (sense CCW) to retrieve the sense information needed for recovery.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Concurrent Sense Facility

      Disclosed is the concurrent-sense facility, which allows
the channel subsystem of ESA/390* systems to retrieve sense
information from a device and present that sense information to the
program along with the I/O interruption that contains the unit-check
status indication.  The facility described herein is the mechanism by
which the sense information is retrieved from the device and the
mechanism by which the sense information is actually returned to the
program. Presenting the status and sense information together allows
the program to realize a performance benefit because it no longer
needs to perform a separate I/O operation (sense CCW) to retrieve the
sense information needed for recovery.  In addition, the device can
be made available for new operations sooner because the contingent
allegiance required to serialize the sense data is not needed.

      A new indicator is defined in the Subchannel Information Block
(SCHIB) of every subchannel.  The indicator is initialized to zero,
indicating that the channel should not retrieve sense information;
that is, the subchannel is not in concurrent-sense mode.
Initializing the indicator to zero provides compatibility for those
programs which have not been modified to recognize when sense
information is being provided with the interruption. The Modify
Subchannel (MSCH) instruction is used by a program to set the
indicator to one, placing this subchannel in retrieve sense
information from the associated device and pass the sense information
to the program whenever the status from the device contains unit
check.  The associated device may be incapable, either for a
particular operation or ever, of returning sense information together
with unit-check status; similarly, the channel may be incapable,
either for a particular operation or ever, of retrieving sense
information together with unit-check status.

      For the ESCON* I/O interface, the supplemental-status facility,
which is a part of the concurrent-sense facility, provides the
mechanism whereby the device supplies basic sense information along
with unit-check status to the channel.  When the program has
indicated concurrent-sense mode in the SCHIB, the channel may, in
turn, indicate to the device that it is permissible to return
supplemental status (sense information) in a status frame.  The
channel indicates to the device that it is permissible to return
supplemental status by using the s...