Browse Prior Art Database

Streamlined Software Channel to Control Unit Interface

IP.com Disclosure Number: IPCOM000103949D
Original Publication Date: 1993-Feb-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Chan, S: AUTHOR [+4]

Abstract

Disclosed are improvements to the protocols between the channel and control unit, which make communication efficient while keeping the function split unchanged. These improvements apply to an S/390* computer with an integrated I/O subsystem, where the S/370* Channel to Control Unit OEMI Interface is replaced by a software interface between a channel task and a control unit task.

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Streamlined Software Channel to Control Unit Interface

      Disclosed are improvements to the protocols between the channel
and control unit, which make communication efficient while keeping
the function split unchanged.  These improvements apply to an S/390*
computer with an integrated I/O subsystem, where the S/370* Channel
to Control Unit OEMI Interface is replaced by a software interface
between a channel task and a control unit task.

      The protocols on the S/370 Channel to Control Unit OEMI
Interface are designed to occur over a hardware bus.  These same
protocols are not efficient when implemented in software with each
item of control data communicated in an intertask message.  The
following paragraphs describe improvements to these protocols for
this software environ- ment.  Refer to the Figure for a typical
example of the improved channel to control unit protocol.

      One improvement to the protocols is in the initiation of data
transfer.  When the control unit task receives a new Channel Command
Work (CCW) command, which requires data to be transferred (1), it is
allowed to accept the command and immediately request a data transfer
in a single intertask message (2).  The channel task processes the
message, as if initial unit status was presented indicating command
acceptance, followed by a request for data transfer.

      Another improvement is related to the performance of a command
chain operation.  When the control unit task presents primary or
secondary status (4), and the conditions are present so...