International Business Machines Corporation

John H Sorg, Jr

Martin W Sachs

Fernando A Luiz

Daniel Francis Casper

Joseph C Elliott

Kenneth R Lynch

John A deVeer

Harlan C Snyder

Edward Loizides

Phillip R Mills

A method and system for pipelining the processing of channel command words is provided. The channel is permitted to send commands and data to the control unit for several channel command words associated with a channel program without having to wait for responses from the control unit for prior commands sent. The channel can pipeline several commands to the control unit and the control unit can then process the commands in the order it receives them. The control unit sends responses to the channel for each command it receives acknowledging receipt of the commands.

Method and system for pipelining the processing of channel command words

Retrying a command from a CCW in a data processing I/O system having a channel connected to a control unit in which the channel detects an error condition and requests the control unit to retry the current command of an I/O operation. The control unit then determines if the requested retry can be accomplished, and, if it can, sends a response back to the channel requesting the channel to initiate a retry. After receiving the response, the channel checks to determine if conditions are still present which allow a retry, and if they are, executes the current command to perform the retry. If the control unit determines that a retry cannot be accomplished, the control unit has the option to perform a unit check procedure. If the control unit determines that neither a retry nor a unit check can be accomplished, the control unit has the option to perform a selective reset function.

Channel-initiated retry and unit check for peripheral devices

Means are provided to prevent the failure of an Initial Program Load (IPL) command in a data processing system because of a 'busy' indication from a Direct Access Storage Device (DASD) control device which is executing the command. An IPL operation from a Central Processing Unit (CPU) involves the issuance of a System Reset signal to all channels and control units connected to the CPU, followed a short time later by a READ IPL command to the DASD control device controlling the DAS device which contains the program to be loaded. The present invention enables the system to distinguish between when a control device is busy with a System Reset procedure and when it is busy on other matters, and to permit the queueing of the READ IPL command when the control unit is busy and there is a System Reset operation pending so that the READ IPL command will not be rejected.

Preventing initial program load failures

A method and means for path independent reservation and reconnection of devices to CPU's operating in a multi-CPU and shared device access system environment. The multi-CPU and shared device access system comprises a plurality of sets of fan out paths (channels), each set coupling a corresponding CPU as a source node; a plurality of input/output devices; and a plurality of control nodes (control units), each node including means for accessing the devices, for selectively intercepting the paths in order to complete a signal path connection to a single destination device. Each control node further includes means (FIG. 2, element 25') for storing a table of independent path sets of CPU's and reserved devices and means (FIGS. 2-5) for managing the connection of CPU's to devices such that for any given selection, reservation or reconnection indication, the table is accessed by at least one control node for ascertaining whether the CPU is a member of a set of interfaces to which the device is reserved, if so, an available path is selected. The control nodes thus allocate dynamically dissimilar path sets to devices and CPU's on an allegiance basis in order to increase the signal path connection probability by the devices to counterpart CPU's involved in the reservation, release, or reconnection of the device and the CPU.

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Los Gatos, CA, United States of America

John H Sorg, Jr