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Get Device Completion Status Subsystem Control Block Command

IP.com Disclosure Number: IPCOM000120635D
Original Publication Date: 1991-May-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 7 page(s) / 263K

Publishing Venue

IBM

Related People

Bonevento, FM: AUTHOR [+2]

Abstract

This article describes a method in which a computer operating system can issue a command to an input/output (I/O) device after additional storage is pinned.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 32% of the total text.

Get Device Completion Status Subsystem Control Block Command

      This article describes a method in which a computer
operating system can issue a command to an input/output (I/O) device
after additional storage is pinned.

      Within a paging operating system, memory areas that are
allocated to an I/O operation or device are "pinned" into storage.
An I/O device or operation may be able to provide additional data
pertaining to the status of the completed I/O operation.  In this
case, a method is needed to notify the operating system that
additional memory is needed and a method is needed of requesting the
additional status from the I/O device.
Read Completion Status Command (RCSB) Overview

      This command is proposed as the means for a host program to
retrieve data concerning a command's completion status.  The
subsystem control block (SCB) architecture requires that the data be
provided from device dependent storage in two instances:
      1.   A device wishes to provide more completion status data to
the host program than can be contained in the 18-byte device
dependent area in the termination status block (TSB).  Data will be
returned for either an SCB or Non-SCB command.  The data area
provided to the host program indicates the command type being
reported.
      2.   The device has encountered a hardware error in completing
a command and can operate to a level where it can provide device
dependent status about the command at the device.  No data needs to
be retained at the device when the device is so damaged that it is
placed in the non-available state.  When data is provided, the format
will be the same as case 1 (more device dependent than can be held in
a TSB). Status data can be for either an SCB or non-SCB command.

      In addition to the two required cases, the architecture allows
an implementation to define the RCSB so that it may be issued after
any command issued to the device or subsystem.  In the case where the
command completed with no error, there is little motivation for using
the new command. When a non-SCB completes with an error, it provides
a means for an implementation to provide details on command failure.
Read Completion Status Detailed Definition

      The Read Completion Status control block command allows a
program in the system unit to retrieve the completion status of an
immediate or control block command from a device.  The data is moved
from the device to an area pointed to by the MA2 field of the control
block command (Memory Address of Completion Status Data).

      Completion status data is transferred to the system unit using
the same semantics as the Read control block command.

      This command must be implemented if a device has the potential
to report more status than can be presented in the TSB, or if the
device has the potential to report status in response to immediate
commands.

      The Read Completion Status command has the opti...