Browse Prior Art Database

Scheduling of Display Buffer Program Execution

IP.com Disclosure Number: IPCOM000062088D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 4 page(s) / 54K

Publishing Venue

IBM

Related People

Haigh, DC: AUTHOR

Abstract

In a display system with several buffers, a buffer program is executed for each display sequentially to generate a picture on each display. To avoid flicker, all programs should ideally be executed in a fixed time which is less than the flicker threshold time. An algorithm is disclosed which ensures that any spare time is distributed between displays. The programs are run in a fixed time unless the total execution time of the program's time exceeds the fixed time, when they are run as often as possible. The algorithm has applications in directed beam and raster displays. This article discloses an improved way of scheduling the execution of display buffer programs of several directed beam displays, so as to reduce the possibility of flicker.

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Scheduling of Display Buffer Program Execution

In a display system with several buffers, a buffer program is executed for each display sequentially to generate a picture on each display. To avoid flicker, all programs should ideally be executed in a fixed time which is less than the flicker threshold time. An algorithm is disclosed which ensures that any spare time is distributed between displays. The programs are run in a fixed time unless the total execution time of the program's time exceeds the fixed time, when they are run as often as possible. The algorithm has applications in directed beam and raster displays. This article discloses an improved way of scheduling the execution of display buffer programs of several directed beam displays, so as to reduce the possibility of flicker. It is also applicable to raster systems where one display buffer update system is shared between several display buffers (devices), and could be used to improve the smoothness of animation of such displays. The description will concentrate on the directed beam case. In a directed beam display system with several displays, to avoid flicker, it is necessary to ensure that all the programs are executed within a certain time Tr. It is also desirable to ensure that the buffer programs are not executed more frequently than a certain rate, because this would cause the pictures to become excessively bright. Usually the fastest re-execution time for the buffer programs is made just less than the flicker threshold time. The technique that is used in the prior art (e.g., the 3250 system) to schedule the starting of the buffer programs for each display is to have a continuously running timer of period Tr. The program for the first display is started at time 0, and as soon as this program has finished, the program for the second display is started and so on, until the buffer programs for all the displays have been executed one after the other. If the total time taken to execute all the buffer programs was less than Tr, then the scheduler waits until the timer has reached time 0 again, when it restarts the program for the first display, and then the others in sequence, as before. This wait ensures that the programs are not executed too frequently (i.e., with a shorter period than Tr). If the total time to execute all the programs was greater than or equal to Tr, then the scheduler restarts the first program immediately. This ensures that when the total execution time is greater than Tr the programs are executed as fast as possible in an attempt to reduce the flicker as much as possible. This scheduling technique suffers from the problem that under certain circumstances some of the displays may appear to flicker even though the total program execution time is less than Tr. This happens when the execution time of one or more of the programs varies, in particular when, on successive executions of a program, it takes alternately more, then less time than the previou...