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Uniform Control Block Format for Computer Systems

IP.com Disclosure Number: IPCOM000102284D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17

Publishing Venue

IBM

Related People

Mandese, EN: AUTHOR [+3]

Abstract

A technique is described whereby a uniform control block format enables devices and subsystems to interface to the Micro Channel* of computer systems. The concept reduces software development time and also structures the input/output command process.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 18% of the total text.

Uniform Control Block Format for Computer Systems

       A technique is described whereby a uniform control block
format enables devices and subsystems to interface to the Micro
Channel* of computer systems.  The concept reduces software
development time and also structures the input/output command
process.

      The format described encodes the field usage within a subsystem
control block (SCB) to allow the system software to determine how the
fields are to be used.  First, it allows an implementation to ensure
that the command word view of field usage in the SCB matches that
which was coded by the program in the SCB enable word.  Second, it
provides an understanding of how the SCB fields are intended to be
used which is independent of the SCB command code.

      Command Control Blocks (CCBs) are used to exchange control and
status information between a client in a system unit and a server in
a feature adapter.  CCBs are variable length areas (up to 256 bytes)
in shared memory address space containing the commands and arguments
passed to a device or subsystem.  These arguments describe the self-
contained operation to be performed.

      When in locate mode, the SCB logical I/O architecture supports
two control block 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 base
control block format is described below:

      Some important characteristics of the CCB are:
      -    CCBs can be chained to other control blocks using memory
addresses.
      -    CCBs are read only to software in the system unit and by a
device or subsystem in a feature adapter, when submitted for
execution.
      -    CCBs can be modified by software in the system unit before
submission or after completion by a device or subsystem.  CCBs are
not modified by a device or subsystem in a feature adapter
      -    CCBs must be aligned on a double-word memory boundary.
      -    Any memory addresses contained within a CCB must be
specified as physical addresses.
      -    A device or subsystem in a feature adapter is only
required to read those control block fields that it needs.

      The base CCB, as shown in Fig. 1, is a variable length
structure created and maintained in shared memory by software in the
system unit. It is used to convey requests to a subsystem or device
in a feature adapter.  These requests are used to direct the
operation of the subsystem or device.  The structure of the base CCB
format, content, meaning and usage of each of its individual fields
is described as follows:
      The Command Word is a 16-bit structured field used to identify
the operation to be performed by a subsystem or device.  The format
of the Command Word is shown in Fig 2.  It is followed by a
description of the content, meaning and usage of each individual
subfiel...