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Asynchronous Channel To Channel Architecture

IP.com Disclosure Number: IPCOM000107297D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 3 page(s) / 112K

Publishing Venue

IBM

Related People

Wu, BH: AUTHOR

Abstract

This article describes an asynchronous channel-to-channel-adapter (CTC) operation. The adapter is an input/output (I/O) device that is normally used by the program in one system to communicate with the program in another system. The adapter provides the buffers and data path for a data transfer between two channels.

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

Asynchronous Channel To Channel Architecture

       This article describes an asynchronous
channel-to-channel-adapter (CTC) operation.  The adapter is an
input/output (I/O) device that is normally used by the program in one
system to communicate with the program in another system.  The
adapter provides the buffers and data path for a data transfer
between two channels.

      Unlike other CTC operation based on the synchronized combined
states and conditions of the adapter on both sides, the asynchronous
CTC operation removes the interdependence. Execution of each
operation depends solely upon the states and the conditions in effect
at the adapter on the side on which the operation is executed.  It is
no longer required for one side of an adapter to synchronize with the
other side in order to complete an operation.

      The adapter is selected and responds in the same manner as an
I/O device.  The two channels connected by the adapter are designated
in this article as channel x and channel y. Both sides of the adapter
perform the same functions.

      The adapter data transfer operations incorporate the "store and
forward" mechanism, whereby data associated with a write command is
stored in the data buffer of the side of the adapter on which the
command is issued, without the need for a dependent command or a
matching command on the other side.  The data is subsequently
forwarded to the data buffer on the other side.  If a read command is
issued on the other side after the data becomes available there, the
adapter performs the data transfer operation for the read command. If
a read command is issued on the other side before the data becomes
available, the adapter requests the deferred retry of the read
command by presenting channel end, status modifier, and unit check
status to the channel.  When the data associated with a write command
on this side becomes available on the other side, the adapter
presents device end status to allow the channel to retry the read
command.

      At a given instant, each side of the adapter can have any one
of three states:  available (A), interruption pending (I), or working
(W).

      The adapter enters the working state when the command is
accepted.

      For an accepted command, the adapter enters the interruption
pending state when device end status is generated.

      After channel end (without device end) status for a command
operation is presented to the channel, the adapter remains in the
working state until the time device end status is generated by the
adapter.

      When a given command is issued on the x side, the state of the
x side of the adapter determines how the command is handled.

      The following cases describe the ada...