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Automatic Correction of Cyclic Realtime Intervals

IP.com Disclosure Number: IPCOM000080000D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Brannon, TL: AUTHOR [+3]

Abstract

One timer queue element can be used to cause repeated interrupts at fixed intervals. This program is used to automatically factor out the interrupt processing time, which would otherwise be added to the interval specified when calculating the time of the next interrupt. The interval can be set up to cycle a specific number of times or indefinitely. Without automatic correction, the significance of the accumulated delay caused by interrupt processing time is directly proportional to the number of interrupts and inversely proportional to the size of the interval.

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Automatic Correction of Cyclic Realtime Intervals

One timer queue element can be used to cause repeated interrupts at fixed intervals. This program is used to automatically factor out the interrupt processing time, which would otherwise be added to the interval specified when calculating the time of the next interrupt. The interval can be set up to cycle a specific number of times or indefinitely. Without automatic correction, the significance of the accumulated delay caused by interrupt processing time is directly proportional to the number of interrupts and inversely proportional to the size of the interval.

The figure is a flow diagram of the steps necessary to implement the automatic correction function in a timer interrupt handler. The address of the timer queue element (TQE) associated with the interrupt is part of the input to the logic in the figure. The TQE contains information necessary for interrupt processing. If the TQE is cyclic and the interrupt does not represent the last interval, the automatic correct logic is entered. The interval specified in the TQE is added to the time of expiration (TOX) of the previous interval and placed in the TQE as the "next time of expiration".

This process continues until the cycle count goes to 0, or the "next time of expiration" is greater than the current time of day (TOD) in the clock. One or more entire cycles can be skipped in the correction process. However, the use of the cycles function is defined so that th...