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Suspension and Restart While Command Chaining

IP.com Disclosure Number: IPCOM000088498D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Cormier, RL: AUTHOR [+2]

Abstract

If a delay condition occurs while an input/output channel is command chaining, for instance, a page fault in a virtual memory, the channel and device controller may be adapted to interact to induce a "Suspend" mode, delaying the associated input/output operation and maintaining device synchronism (rather than terminating the operation and having it restarted ab initio by a new Start I/O, etc.).

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Suspension and Restart While Command Chaining

If a delay condition occurs while an input/output channel is command chaining, for instance, a page fault in a virtual memory, the channel and device controller may be adapted to interact to induce a "Suspend" mode, delaying the associated input/output operation and maintaining device synchronism (rather than terminating the operation and having it restarted ab initio by a new Start I/O, etc.).

IBM System/360, 370 channels may be adapted to signal such occurences to associated device controllers via existing lines on the I/O interface. The sequence Service Out following Status In normally is interpreted by the controller as an "Accept Status" signal requiring the controller to disconnect after Select Out falls.

Coincident with the foregoing Service Out, the channel may present one of two "special' command signals (hexadecimal `00' or `01') on Bus Out. If the controller is adapted to respond to these command signals, it will interpret `00' as designating normal Accept Status mode and `01' as designating suspended mode of operation. In the normal (00) mode the controller operates conventionally and interprets this as a normal ending to a command chain. In the suspended (01) mode the controller must maintain allegiance to the channel and await reselection for the next command of the chain.

An unadapted controller would not recognize the foregoing special command signals and operate only in normal mode. If an `01' command...