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Input/Output Operation Asynchronous STATUS Reporting Technique

IP.com Disclosure Number: IPCOM000038456D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Bourke, DG: AUTHOR [+4]

Abstract

This article describes a technique for use in the input/output (I/O) subsystem of a data processing system that provides for status reporting in line with an asynchronous I/O operation to eliminate additional status reporting operations. Fig. 1 illustrates a representative set of essential I/O command (Image Omitted) parameters for starting and I/O operation. The size of fields chosen for the illustration is arbitrary. The parameters are: .The command byte; The I/O address showing a field for specifying up to four main I/O; busses which may be attached to a processor and a field for specifying the address of the target device. A storage address pointing to an I/O control block (IOCB) in the main storage of the processor.

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Input/Output Operation Asynchronous STATUS Reporting Technique

This article describes a technique for use in the input/output (I/O) subsystem of a data processing system that provides for status reporting in line with an asynchronous I/O operation to eliminate additional status reporting operations. Fig. 1 illustrates a representative set of essential I/O command

(Image Omitted)

parameters for starting and I/O operation. The size of fields chosen for the illustration is arbitrary. The parameters are: .The command byte; The I/O address showing a field for specifying up

to four main I/O; busses which may be attached to a

processor and a field for specifying the address of the

target device.

A storage address pointing to an I/O control block

(IOCB) in the main storage of the processor. These parameters are passed to a specified device on the appropriate I/O bus, and are called the immediate command parameters (ICPs). On receipt of the ICP by the device, the processor disconnects and the device proceeds in a manner asynchronous to the processor, fetching the IOCB and carrying out the operation. When the operation is complete, the device reconnects to the processor program by means of an end interrupt. The IOCB depicted in Fig. 1 is located in the main storage of the processor and specifies the asynchronous part of the I/O operation.

It contains more specific definitions of the operation to be performed, such as definitions of main storage areas for data and status reports, and so forth. It has a fixed length of eight words and is read-only by the device. The IOCB contains two parameters relevant to the asynchronous status reporting mechanism. They are:
.the status address, and THE STATUS COUNT. The status address pointer specifies the beginning storage location where the device is to store all completion status of the operations. The status count specifies the maximum size of the status area allocated by the program for the operation. All status is posted to storage in the status area prior to posting the interrupt signaling completion of the I/O operation.

This allows the IOCB to be of a fixed length, while lifting limitations on the amount of status that can be reported. It provides for both normal and exception status reporting inline with the execution of one I/O operation, thus eliminating the necessity for the program to initiate another I/O operation with its attendant interrupt to specifically read exception status. Consequently, for environments where the data characteristics or course of an I/O operation is not well known a priori by the program (e.g., communications), a dramatic decrease in interrupt activity will result. It makes the device more available to the program, because it lifts the constraint that the device is a serially reusable resource until the operation to specifically read status is completed. Fig. 2 presents...