Browse Prior Art Database

Move Mode Subsystem Control Block Commands with Conditional Execution

IP.com Disclosure Number: IPCOM000115142D
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 100K

Publishing Venue

IBM

Related People

Bonevento, FM: AUTHOR [+3]

Abstract

Disclosed is a facility allowing the execution of a command to be skipped if a specified condition is met. Typically, the condition is indicated by the value stored at a location in computer memory. Such a facility provides for the conditional execution of Control Elements by a subsystem without the execution of instructions in the host computer.

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This is the abbreviated version, containing approximately 52% of the total text.

Move Mode Subsystem Control Block Commands with Conditional Execution

      Disclosed is a facility allowing the execution of a command to
be skipped if a specified condition is met.  Typically, the condition
is indicated by the value stored at a location in computer memory.
Such a facility provides for the conditional execution of Control
Elements by a subsystem without the execution of instructions in the
host computer.

      Since the conventional SCB (Subsystem Control Block) move mode
command set does not provide such a facility, two new Control
Elements, SKIP and SKIP IMMEDIATE, are defined, in Request, Reply,
and Error types.  The functions of the Request form of these Control
Elements are to execute a test defined in the (SKIP RELATION) and to
skip the next Control Element accessed if the (SKIP DIRECTION) given
in the Control Element is met.

      The Figure shows the formats of the Request types of these
Control Elements.  If the I field is equal to one in the Request
format, the Byte Count and Pitch values are not contained in the
Control Element, which instead contains the location of these fields.
The Skip Relation is tested using two comparands.  In the Skip
Immediate case, one comparand is given an immediate value in the
Control Element, and the other is located using a comparand address
given in the Control Element.

      The Skip Relation (SR) is a binary encoded 8-bit field in the
Control Element, which defines the logical relationship to be tested.
Codes in this field indicate whether this relationship is equal (=),
not equal (<>), less than (<), greater than (>), less than or equal
(<=), or greater than or equal (>=).

      The Skip Direction (SD) is an 8-bit value which is encoded as
'01'x to indicate a Skip True (ST) condition or as '00'x to indicate
a Skip false (SF) condition.  With the ST condition the next control
word is skipped if the Skip Relation is true.  With the SF condition,
the next control word is skipped if the Skip Relation is false.

      The type of comparison performed between the comparands is
determined by the 8-bit Comparison Type (CT) field in the Control
Element.  If this field is encoded as '00x' a string comparison is
performed on a byte by byte basis using the compara...