Browse Prior Art Database

Method of Keeping And Synchronizing Time in a Message-Passing Distributed System

IP.com Disclosure Number: IPCOM000100734D
Original Publication Date: 1990-May-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 4 page(s) / 150K

Publishing Venue

IBM

Related People

Harper, RW: AUTHOR

Abstract

This article describes integrating the reference time clock in the bus interface device in a message-passing distributed systems. The invention has application to message-passing distributed systems interconnected by a parallel bus and those systems interconnected by a local area network where the propagation delay is less than the clock resolution. The invention has little or no application to shared memory distributed systems.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 47% of the total text.

Method of Keeping And Synchronizing Time in a Message-Passing Distributed System

       This article describes integrating the reference time
clock in the bus interface device in a message-passing distributed
systems.  The invention has application to message-passing
distributed systems interconnected by a parallel bus and those
systems interconnected by a local area network where the propagation
delay is less than the clock resolution. The invention has little or
no application to shared memory distributed systems.

      In a loosely coupled, message passing distributed system, it is
desirable to maintain a synchronized reference time (i.e., Time of
Day or Time of Epoch) in each member.  This reference can be used,
for example, to time tag errors or external events or synchronize
execution of processes in different members.  In message-passing
distributed systems, each member is an autonomous processor.  Many
systems use bus interface devices which are commanded by the
processor to perform data transfers.  When one member wishes to share
data with another, it commands the bus interface device which, in
turn, requests mastership of the bus.  When the current transfer
completes, a bus arbitration sequence determines which member can
next control the bus.  The program commanding the bus interface can
continue executing and, upon completion, the device will notify the
member and return the status of the operation.

      By making the reference time clock an integral part of the bus
interface device, as shown in the figure, the bus interface device
will contain circuitry to increment the reference time value at the
proper interval.  When the reference time is required, a value is
returned.  When a processor is required to synchronize the reference
time in all the members, it issues a message causing all other clocks
to be set to its own.

      During Normal Operation a clock pulse supplied to the bus
interface device causes its reference's time value to be incremented
at the proper interval.  When the member's processor requires the
current reference time value, it issues a command to the bus
interface device which returns the current value.

      The preferred procedure for setting and resetting the reference
time would be as follows:
A)   The member given the  responsibility of setting or resetting of
the reference value loads a holding buffer in its bus interface
device with the desired reference time. This holding register is
incremented via the same clock pulse used to update the reference
time register.
B)   The process of loading the holding buffer causes the member's
bus interface device to issue a request for control of the bus.
C)   When mastership of the bus is obtained, the bus interface device
transfers the contents of the holding buffer to the reference time
register.  It also formats a bus command to broadcast its new
reference time value to the other members.
D)   The other members' bu...