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Browse Prior Art Database

Method of Indirect Data Addressing

IP.com Disclosure Number: IPCOM000111339D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 75K

Publishing Venue

IBM

Related People

Arnold, ME: AUTHOR [+3]

Abstract

Current indirect data addressing methods apply various boundary alignment and/or length requirements. These requirements result in excessive data movement and inefficient I/O. Described is a method to allow for arbitrary boundary and lengths as embodied in a ES/370 specific implementation.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Method of Indirect Data Addressing

      Current indirect data addressing methods apply various boundary
alignment and/or length requirements.  These requirements result in
excessive data movement and inefficient I/O.  Described is a method
to allow for arbitrary boundary and lengths as embodied in a ES/370
specific implementation.

      CCW modified indirect data addressing permits a single channel
command word to control the transfer of data that spans noncontiguous
pages in real main storage, in much the same way as indirect data
addressing.  The use of CCW modified indirect data addressing also
allows the program to designate data addresses above 16M for both
format-0 and format-1 CCWs.

      CCW modified indirect addressing is specified by a flag in the
CCW (bit xx) which, when one, indicates that the data address is not
used to directly address data.  Instead, the address points to a
header and a list of double words.  Collectively, the addressed
structure is called a Modified-Indirect-Data-Addressing-List (MIDAL)
and the list of words as Modified-Indirect-Data-Addressing-Words
(MIDAWs), each of which contains an absolute address designating a
data area in main storage and a length of that storage.

      When the modified-indirect-addressing bit in the CCW is one,
the data-address field of the CCW designates the location of the
MIDAL to be used for data transfer for the command.  The count of the
number of MIDAWs is contained in the first word, with each MIDAW in
successive locations in storage.

      Each MIDAW is used for the transfer of up to 64K bytes, the
current CCW limitation.  The MIDAL designated by the CCW can be at
any location.  Data is then transferred, for read, write, control,
sense ID, a...