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Dedicated Interval Timer

IP.com Disclosure Number: IPCOM000081435D
Original Publication Date: 1974-Jun-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Brannon, TL: AUTHOR [+3]

Abstract

System performance can be improved by dedicating an interval timer to the task dispatcher, for use in the time slicing and dynamic dispatching functions. In the cases of both time slicing and dynamic dispatching, the dispatcher must, before giving control to a task, set up a time interval that will cause a timer interrupt when the task has run for the specified amount of time.

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Dedicated Interval Timer

System performance can be improved by dedicating an interval timer to the task dispatcher, for use in the time slicing and dynamic dispatching functions. In the cases of both time slicing and dynamic dispatching, the dispatcher must, before giving control to a task, set up a time interval that will cause a timer interrupt when the task has run for the specified amount of time.

On systems that have the standard interval timer plus the Clock Comparator and CPU Timer, the standard interval timer is reserved for the exclusive use of the dispatcher. The Clock Comparator is used for all realtime intervals, while the CPU Timer is used for all task-time intervals other than the time slicing and dynamic dispatching intervals.

When a task is dispatched that is either time sliced or dynamically dispatched, the only logic necessary for the dispatcher to set up the time interval on the standard interval timer is one instruction, to move the time value into the interval timer. Without a dedicated timer, the dispatcher must have the request placed in a queue of requests. A significant amount of logic is required to search for the correct place in the queue, chain the element into the queue, and adjust the interval time based on the amount of time that any elements on the queue ahead of it have to run.

When the interval expires, no second level timer interrupt handler is needed. The first level timer interrupt handler can pass control directly to the dis...