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New I/O Subsystem Command: Read Command Set

IP.com Disclosure Number: IPCOM000122400D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04

Publishing Venue

IBM

Related People

Wagner, RE: AUTHOR

Abstract

From time to time one software development group or another requests some indication from a subsystem whether a given command or subcommand is supported. When these questions arise, there are always two questions that are raised. The first question deals with the command or subcommand itself in terms of its inclusion on exclusion from a given architecture. The second question deals with the use of the limited real estate (space) within a Read Device Characteristics type data field. This problem can be avoided in the future by defining a new subsystem command that is all inclusive.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 22% of the total text.

New I/O Subsystem Command: Read Command Set

      From time to time one software development group or
another requests some indication from a subsystem whether a given
command or subcommand is supported.  When these questions arise,
there are always two questions that are raised.  The first question
deals with the command or subcommand itself in terms of its inclusion
on exclusion from a given architecture.  The second question deals
with the use of the limited real estate (space) within a Read Device
Characteristics type data field.  This problem can be avoided in the
future by defining a new subsystem command that is all inclusive.

      This new command should have the following characteristics.
      *  Include all commands that are supported per subsystem per
device type.
      *  Extendable to include new commands as well as new
subcommands or orders for individual commands.
      *  Flexibility in terms of further describing a given command
in greater detail.

      The new command returns data about the commands supported by
the subsystem for the attached addressed device.  The data returned
by this command is divided into two major areas.

      The first area is a bit map which has an assigned bit for each
possible command code.  If a given command is supported by the
subsystem for the addressed device, the bit is set to binary one;
else, it is set to binary zero.  Using this technique, the command
codes for a one-byte command code value can be represented in 32
bytes (256 bits) by using the relative bit position to implicitly
identify the command code.

      The second area is composed of a further description of one or
more of the commands in further detail.  Commands that would be
further described include those commands which have subcommands or
orders as well as commands with multiple options.  The general
structure of this area is similar to that of the primary command area
in that it has a bit map that signals the availability of a
subcommand or an option. In addition, a header is required to
indicate what command is being described and how it is being
described.  With this header it is possible to describe a given
command in one or more areas.  For example, it can be used to
describe a command such as Perform Subsystem Function in terms of its
orders, as well as being able to describe suborders of a specific
order.

      The general format of the data returned is given in Table 1.
      Implementation:

      A new command, Read Subsystem Command Set, would return a data
field that would indicate what commands and subcommands are supported
for the addressed device via the attaching subsystem.  The format for
the data return is as follows.
x'00-01'
      The length of the data returned.  The decimal length of the
data field is 34*(c + 1), where c is the number of commands with
extended definitions.
x'02-21'
      This field defines which commands ar...