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Termination Status Blocks as Defined in the Subsystem Control Block for Micro Channel

IP.com Disclosure Number: IPCOM000121323D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 8 page(s) / 283K

Publishing Venue

IBM

Related People

Bonevento, FM: AUTHOR [+6]

Abstract

This article describes the structure and function of termination status blocks (TSBs) which are areas in shared memory address space used by a device or subsystem to report the ending status of a control block command to the software in a computer system unit. The location of the TSB is contained in the TSB address field of the control block for MICRO CHANNEL* in which it is used.

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This is the abbreviated version, containing approximately 23% of the total text.

Termination Status Blocks as Defined in the Subsystem Control Block
for Micro Channel

      This article describes the structure and function of
termination status blocks (TSBs) which are areas in shared memory
address space used by a device or subsystem to report the ending
status of a control block command to the software in a computer
system unit.  The location of the TSB is contained in the TSB address
field of the control block for MICRO CHANNEL* in which it is used.

      Fig. 1 shows the structure of a TSB in block diagram. It is
structured so that the status information it contains may be read and
interpreted by software in the system unit in a uniform manner,
regardless of the control block command executed.  This generic
formatting provides the following benefits:
@    Software in the system unit can determine before storing a TSB
the maximum amount of memory to be allocated for the TSB
independently of the subsystem.
@    As a result of knowing the maximum size of a TSB, software in
the system unit can define TSB memory allocated boundaries before
actual storing takes place, thus preventing a subsystem or device
from overwriting non-TSB memory areas.

      The TSB area must not be modified by software in the system
unit when its associated control block has been delivered to the
subsystem for execution and remains incomplete.  The system software
should initialize the End Status Word 1 field in the TSB to zero
prior to delivering the control block to the subsystem.  This allows
the Software to do a simple non-zero check of the End Status Word 1
field in the TSB to determine whether or not TSB status was stored on
control block command completion.

      Any control block in a chain may request the storing of TSB
status on normal completion of the associated control control block
command.  TSB Status is always to be stored when a control block is
suspended, terminated by an error, reports a suppressed error or
follows a conditional command chain.  TSB status when associated with
subsystem interrupts of the system unit allows a program to monitor
progress of a device through a chain of control block commands.

      In Locate mode, the subsystem control block logical I/O
architecture supports two TSB structures, base and extended. The
difference between them is in the format, content, meaning and usage
of the information contained in the individual fields of each.  The
following sections describe these TSBs.
BASE TERMINATION STATUS BLOCK STRUCTURE

      The base TSB structure is shown in Fig. 2.  It is used by a
device or subsystem to report the ending status of a base control
block command to the software in the system unit.  A base TSB is
always 32 bytes in length.

      A description of the format, content, meaning and usage of each
of its individual fields follows.
End Status Word 1

      End Status Word 1 is a 16-bit structured field used to hold
status flags indicating how a...