Browse Prior Art Database

Dynamic Filtering of Digitizer Points for Pen-Based Computers

IP.com Disclosure Number: IPCOM000106378D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 81K

Publishing Venue

IBM

Related People

Kannan, K: AUTHOR [+5]

Abstract

Described is an architectural implementation to provide dynamic filtering of digitizer points, as used with pen-based computers, to minimize the number of interrupts.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Dynamic Filtering of Digitizer Points for Pen-Based Computers

      Described is an architectural implementation to provide dynamic
filtering of digitizer points, as used with pen-based computers, to
minimize the number of interrupts.

      Typically, pen-based computers rely on complex software to
process digitizer points through their recognition algorithms.  Large
numbers of digitizer interrupts will reduce the time available for
character recognition, thereby making real time character recognition
time consuming.  Generally, a digitizer will generate two hundred
samples/second at approximately five bytes/sec.  If an interrupt is
generated for each byte, a considerable amount of system time can be
spent on interrupt overhead.

      The concept described herein provides a means of minimizing the
number of system interrupts related to the digitizer points by
filtering the data through a dynamic discard window in the digitizer
controller and only reporting data that survives the filtering.  By
dynamically varying the digitizer sampling rate, interrupting the
system processor only occurs when one or more complete points have
been assembled by the digitizer controller.

      Digitizer points are typically classified as 'pen down',
'proximity', and 'out of proximity' points.  A pen down point is a
digitizer x,y coordinate pair generated while the stylus is touching
the screen.  A proximity point is a digitizer x,y coordinate
generated while the stylus is hovering above the screen within
proximity distance.  An 'out of proximity' point is a point detected
by the digitizer, but the digitizer is out of range.  Another method
in a digitizer subsystem relates to the 'transition point' which is a
digitizer point whose type is different than the type of the previous
point, such as a pen down point that follows a proximity point.

      In order to reduce the number of reported interrupts, a service
processor (SP) is used in conjunction with the central processing
unit (CPU) to generate a square discard window within which the
digitizer points will not report to the host CPU.  The host may
activate or deacti...