Browse Prior Art Database

Conditional Skip Control Elements

IP.com Disclosure Number: IPCOM000116956D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 8 page(s) / 323K

Publishing Venue

IBM

Related People

Bonevento, FM: AUTHOR [+3]

Abstract

Disclosed are several control elements, providing means for conditionally skipping the execution of move mode control elements within the Subsystem Control Block (SCB) architecture. The disclosed control elements are defined in Request, Reply, and Error types.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 21% of the total text.

Conditional Skip Control Elements

      Disclosed are several control elements, providing means for
conditionally skipping the execution of move mode control elements
within the Subsystem Control Block (SCB) architecture.  The disclosed
control elements are defined in Request, Reply, and Error types.

      The SKIP and SKIP IMMEDIATE control elements will be discussed
first, with particular reference being made to Figs. 1-5.  The
Request form of these control elements allows the executing entity to
operate on a set of SCB move mode commands under control of memory
locations shared between the requesting and executing entity.  For
example, this method can be used to control buffer access by an
adapter.  Using a value in buffer locations, this control element can
be used to avoid executing the next element in a chain when the
buffer is not ready to be read or written by the adapter.  Also, this
control element can be used to control virtual page stealing and
loading, testing the external page table of an operating system while
allowing the adapter to schedule paging operations dependent on field
settings in the table.  In this way, a page stealing loop is executed
by a intelligent adapter instead of in a control program, allowing
the system to run other tasks faster.

      Fig. 1 shows the format of the Request form of these control
elements.  In the SKIP control element, the last field is for the
Address of Comparand 2, while in the SKIP IMMEDIATE control element,
the last field is for the Immediate Value of Comparand 2.  The
function of these control elements is to allow a client to skip
execution of the next sequential control element if a specified
condition, defined in the Skip Relation (SR), is met.  The next
sequential control element may be an element of a current chain of
control elements or a next control element not in the chain.  If the
SKIP or SKIP IMMEDIATE request control element is an element other
than the last element of the chain, the next chain element is
skipped.  If this request control element is not part of a chain, or
if it is the last element of a chain, the next sequential control
element directed to the same entity is skipped.  In these formats, if
the I field is equal to zero, the byte count and pitch values are
contained within the control element.  If the I field is equal to
one, the fields for these values instead contain the locations of the
fields where the values are stored.

      Fig. 2 shows the encoding of the SR operand, defining the
logical relationship to be tested, using two comparands, in a
binary-encoded eight-bit field of the control element.  In the SKIP
control element, these comparands are located using two comparand
addresses given in the control element.  In the SKIP IMMEDIATE
control element, 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 Direction (S...