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Browse Prior Art Database

Deriving Exact Timing Information for Synchronization of Real Time Processes

IP.com Disclosure Number: IPCOM000107942D
Original Publication Date: 1992-Apr-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 103K

Publishing Venue

IBM

Related People

Medan, Y: AUTHOR [+2]

Abstract

Disclosed is a new software approach for deriving exact timing information for maintaining real-time synchronization between two related tasks, while each works at a different clock rate. A process such as sampling rate conversion can exploit such an exact timing information. Benefits arise in a multimedia environment where multiple real-time processes have producer-consumer task pairs that are working at different rates and are required to remain in synchronization with respect to each other. An example is audio sampling rate conversion process where an A/D task samples audio at a given input rate and a D/A task needs to output the data at a different rate in real-time, without causing overflow or overrun of samples.

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Deriving Exact Timing Information for Synchronization of Real Time Processes

       Disclosed is a new software approach for deriving exact
timing information for maintaining real-time synchronization between
two related tasks, while each works at a different clock rate.  A
process such as sampling rate conversion can exploit such an exact
timing information.  Benefits arise in a multimedia environment where
multiple real-time processes have producer-consumer task pairs that
are working at different rates and are required to remain in
synchronization with respect to each other.  An example is audio
sampling rate conversion process where an A/D task samples audio at a
given input rate and a D/A task needs to output the data at a
different rate in real-time, without causing overflow or overrun of
samples.

      The scheme is based upon the observation that, typically, the
ratio between the clock rates of the tasks that comprise a real-time
process can be expressed as a rational number M/N which is less than
or equal to 1.  This means that N corresponds to the higher clock
rate of the two clocks.  The novelty is that it exploits the fact
that this number is rational in order to efficiently derive exact
timing information that can be used to synchronize the two tasks.
Timing derivation involves a simple counter that gets updated at the
higher clock rate by an increment of (M Modulo N).  The value of the
counter div ided by N represents the exact timing of the fast clock
tick relative to the most recent slow clock tick instant.  In this
manner exact timing information is derived without any drift which is
typical in prior-art techniques.

      In many multimedia and communication systems, data is produced
at one rate but should be consumed, in real-time, at a different rate
because the producer and consumer tasks are controlled by separate
clocks.  Prior-art techniques used to solve this problem express the
rate of each of the tasks involved using a common denominator clock
rate.  The problem associated with this approach is that the common
clock interval cannot, in many cases, be expressed precisely by a
finite word-length fraction.  Due to...