Browse Prior Art Database

Timing Dependencies and Command Retry

IP.com Disclosure Number: IPCOM000081198D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Dugan, RJ: AUTHOR

Abstract

In U. S. Patent 3,688,274, Command Retry Control by Peripheral Devices, Cormier et al., there is described a data channel in which a control word containing a command is retained in a backup register. Upon the occurrence of a signal from an attached control unit, a retry of the retained command is accomplished without interrupting the computer to retry the original initializing command, even though intervening control words were executed.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 66% of the total text.

Page 1 of 2

Timing Dependencies and Command Retry

In U. S. Patent 3,688,274, Command Retry Control by Peripheral Devices, Cormier et al., there is described a data channel in which a control word containing a command is retained in a backup register. Upon the occurrence of a signal from an attached control unit, a retry of the retained command is accomplished without interrupting the computer to retry the original initializing command, even though intervening control words were executed.

In the present IBM System/370 interface all selection sequences, whether channel or control unit initiated, cannot take longer than 32 microseconds of delay at the control unit. The command retry function can be utilized to enable the design of control units, which exceed the 32 microsecond time limit. This is accomplished by indicating command retry status, without device end, whenever a start I/O command is executed. condition code of zero (indicating that the I/O operation has been initiated and the channel is proceeding with its execution) is returned to the central processor. When the control unit is ready to return the proper status, the device end status is returned signalling the channel that retry is now to be performed. Since the control unit has already handled the initial selection sequence, the time interval is maintained well within the 32 microsecond limit.

The flow chart shows the modification necessary to Fig. 5A of the above- mentioned patent to accommodate the added functi...