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Browse Prior Art Database

Timing Algorithm for a High-Resolution Timer

IP.com Disclosure Number: IPCOM000117269D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Nigam, A: AUTHOR [+2]

Abstract

Disclosed is a method for enabling an High Resolution Timer (HRT) using two controllers, so that the timer, being disabled when it is not in use, is prevented from interrupting uselessly when it is not needed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 68% of the total text.

Timing Algorithm for a High-Resolution Timer

      Disclosed is a method for enabling an High Resolution Timer
(HRT) using two controllers, so that the timer, being disabled when
it is not in use, is prevented from interrupting uselessly when it is
not needed.

      Without the presently-disclosed method, the IBM PC AT*
architecture limits the abilities of an Intel 8254 HRT chip tied to
IRQ0 (Interrupt Request 0), driving the clock line at 1.193182 MHz.

      With the presently-disclosed method, when a process is present
requiring high-resolution timing, a main controller controls
operation of the HRT chip, programming the chip to interrupt
constantly, in a Rate Generator Mode, and handling interrupts as the
occur.  When no such process is present, a helper controller,
operating at each interrupt of the system clock (for example, every
32 ms), changes a number stored in the counter of the HRT chip to a
value greater than that which is decremented to zero before the next
system clock interrupt.  Since the number is therefore never
decremented to zero, no interrupts occur in this Interrupt on
Terminal Count Mode.

      When a first process calls for a fast interrupt rate, the
helper controller ceases operation, as the main controller programs
the chip for a fast rate and begins handling interrupts in the Rate
Generator Mode.  As more processes ask for a faster rate, they are
handled at a rate they require.  A process counter keeps track of all
the activ...