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Extending Control Blocks Used in the Micro Channel

IP.com Disclosure Number: IPCOM000101369D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 9 page(s) / 375K

Publishing Venue

IBM

Related People

Bonevento, FM: AUTHOR [+2]

Abstract

Described is a uniform methodology to interface devices and subsystems to a MICRO CHANNEL* in a computer system through the use of a uniform extension to the subsystem control blocks. The format and definitions used in the extended control blocks are described.

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

Extending Control Blocks Used in the Micro Channel

       Described is a uniform methodology to interface devices
and subsystems to a MICRO CHANNEL* in a computer system through the
use of a uniform extension to the subsystem control blocks.  The
format and definitions used in the extended control blocks are
described.

      The extended system control block (SCB) format has the
following additional attributes:
        - Two buffer addresses and two buffer lengths
        - Extended Enable Word to provide additional function
        - Chain identification field

      There are two formats for a control block: basic and extended.
The basic format is shown in Fig. 1, and the extended format is shown
in Fig. 2.  The extended format consists of the basic format with
some additional fields added at the end.

      With the exception of the SCB words, all words in the extended
SCB remain as defined in the Base SCB word definitions.  A brief
definition of the various fields shown in Figs. 1 and 2 is as
follows:
  Command Word - Used to define the type of command.  It consists of
three fields.
  Enable Word 1 - The format of this field, as shown in Fig. 3, is
the same for both the extended and the base control block.  The
content, meaning and usage of affected flags are as follows:
            Flag - Name and Function:
            CNE  Chain No Error - The content, meaning and usage of
this flag is the same for both the extended and the base control
block.
            CC   Conditional Chaining - The content, meaning and
usage of this flag is the same for both the extended and the base
control block.
            CCS  Chain Condition Specification - The format, content,
meaning and usage of this sub-field is the same for both the extended
and the base control block.
   MA1  Memory Address 1 selected - The MA1 selected flag (bit

      5) is used to indicate whether or not the contents of the MA1
field of the control block is to be used as the physical address for
the operation defined by the control block.  If the MA1 selected flag
is set to one, MA1 is to be used.  When set to zero, MA1 may
be used as a device-dependent field.  The table shows the usage and
restrictions for the MA1 selected flag when used in conjunction with
the memory address 2 (MA2) selected flag, the extended structure
(EXT) flag, and the indirect list 1 (IL1) flag.  The table shows
details of usage of Enable Word 1 flag settings.
   MA2  Memory Address 2 selected - The MA2 selected flag (bit 6) is
used to indicate whether or not the contents of the MA2 field of the
control block is to be used as the physical address for the operation
defined by the control block.  If the MA2 selected flag is set to
one, MA2 is to be used.  When set to zero, MA2 may be used as
a device-dependent field.  The table shows the usage and restrictions
for the MA2 selected flag when used in co...