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I/O Event Synchronization With an Express Dispatch/Descend Mechanism

IP.com Disclosure Number: IPCOM000078820D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 60K

Publishing Venue

IBM

Related People

Edel, TR: AUTHOR

Abstract

All user tasks in IBM OS/360, voluntarily suspended as a result of their waiting for an external event, relinquish CPU control by issuing a WAIT service that results in a task switch. When the event occurs, the interrupt is processed by a common interrupt service routine before invoking the POST service. POST checks to see if the event just completed is sufficient to warrant the owning event task's return to execution status (i.e., a task switch). The following steps occur in OS/360 for event synchronization and task activation/deactivation. (Image Omitted)

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I/O Event Synchronization With an Express Dispatch/Descend Mechanism

All user tasks in IBM OS/360, voluntarily suspended as a result of their waiting for an external event, relinquish CPU control by issuing a WAIT service that results in a task switch. When the event occurs, the interrupt is processed by a common interrupt service routine before invoking the POST service. POST checks to see if the event just completed is sufficient to warrant the owning event task's return to execution status (i.e., a task switch). The following steps occur in OS/360 for event synchronization and task activation/deactivation.

(Image Omitted)

In contrast, an Express Dispatch/Descend Mechanism designed for direct association of user tasks with external events performs the following functions:
A. Directly connects a problem program user task to an interrupt

source (may be shared). The event is uniquely described by

an SCP address that is specified at I/O request time, and

returned at interrupt completion to directly locate the

correct user task. This is schematically portrayed below:

(Image Omitted)

The SCP Pointer is used to eliminate the randomness of the

Completed, event by directly associating it with an internal

SCP Control Block. Searching a device table to find a

matching entry is thus eliminated.
B. Merges the interrupt priority with the priority of a user

task. Thus Interrupts are no longer higher in priority

than any enabled problem program task, since each user

Task Control Block contains a mask field which is loaded

into a Control Register upon Task Dispatch Time.

The setting of the Har...