Browse Prior Art Database

Cancelling Command Retry With Jump Function

IP.com Disclosure Number: IPCOM000081662D
Original Publication Date: 1974-Jul-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Cormier, RL: AUTHOR [+2]

Abstract

Control units are frequently shared between devices where one is an output device and the other is an input device. Sometimes only one device exists, but two separate functions are possible, namely input and output. The control unit must provide either two separate buffers (one for input and one for output) or use one buffer and serially accomplish the input and output functions. A performance problem develops when a single-channel program is utilized for both operations, and the control unit's microprocessor is unable to determine the buffer(s) state(s) within the time allowed on the interface between channel and control unit.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 58% of the total text.

Page 1 of 1

Cancelling Command Retry With Jump Function

Control units are frequently shared between devices where one is an output device and the other is an input device. Sometimes only one device exists, but two separate functions are possible, namely input and output. The control unit must provide either two separate buffers (one for input and one for output) or use one buffer and serially accomplish the input and output functions. A performance problem develops when a single-channel program is utilized for both operations, and the control unit's microprocessor is unable to determine the buffer(s) state(s) within the time allowed on the interface between channel and control unit. For example, when a "Write" command is received from the channel by the control unit interface adapter, the appropriate initial status is not known until the microprocessor is interrupted and the appropriate buffer is checked.

The conditions that may exist at the buffer are (1) the buffer is free to execute the write operation; (2) the buffer is in the middle of a previous write operation, or
(3) the buffer has just been asynchronously loaded with "read" data. Condition
(1) is the only allowable state that insures proper execution of the new "write" command. Since the time limit will more than likely be exceeded just to interrogate the buffer state, command retry status could be returned without device end. (See U. S. Patent 3,688,274--"Command Retry Control By Peripheral Devices" Cormier et al.)...