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Input/Output Control Block Restart Command

IP.com Disclosure Number: IPCOM000038459D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Bourke, DG: AUTHOR [+3]

Abstract

This article describes a technique for use in the input/output (I/O) subsystem of a data processing system which eliminates the necessity for I/O devices to refetch control blocks for restarting an I/O operation. The command that normally initiates an I/O operation is a Start command. The drawing illustrates a representative set of essential I/O command parameters for starting an I/O operation. The size of fields chosen for the illustration is arbitrary. The parameters are: The command byte . The I/O address, 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 the I/O device on the appropriate I/O bus by the processor program.

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Input/Output Control Block Restart Command

This article describes a technique for use in the input/output (I/O) subsystem of a data processing system which eliminates the necessity for I/O devices to refetch control blocks for restarting an I/O operation. The command that normally initiates an I/O operation is a Start command. The drawing illustrates a representative set of essential I/O command parameters for starting an I/O operation. The size of fields chosen for the illustration is arbitrary. The parameters are: The command byte . The I/O address, 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 the I/O device on the appropriate I/O bus by the processor program. On receipt of the command 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 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 control, data and status. It has a fixed length of eight words and is read-only by the device. Provision is made for an I/O operation to be restarted by the following means.

The I/O device holds the image of the IOCB in execution. The IOCB ca...