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Browse Prior Art Database

External Time Reference Synchronization Facility

IP.com Disclosure Number: IPCOM000104818D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 6 page(s) / 174K

Publishing Venue

IBM

Related People

Mall, MG: AUTHOR [+7]

Abstract

Disclosed is a method for synchronizing time-of-day (TOD) clocks of Central Processing Complexes (CPCS) at remote locations with nanosecond accuracy. The invention uses an external device, called External Time Reference (ETR). The ETR has an internal reference clock to provide necessary signals for establishing and maintaining synchronization between TOD clocks of a CPC and the reference clock of the ETR. When TOD clocks of different CPCs are synchronized to the reference clock of the ETR, the clocks are running in synchronism with respect to each other.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 34% of the total text.

External Time Reference Synchronization Facility

      Disclosed is a method for synchronizing time-of-day (TOD)
clocks of Central Processing Complexes (CPCS) at remote locations
with nanosecond accuracy.  The invention uses an external device,
called External Time Reference (ETR).  The ETR has an internal
reference clock to provide necessary signals for establishing and
maintaining synchronization between TOD clocks of a CPC and the
reference clock of the ETR.  When TOD clocks of different CPCs are
synchronized to the reference clock of the ETR, the clocks are
running in synchronism with respect to each other.

      An ETR provides a number of ports which can be connected to
CPCs.  Two ETRs may be connected (coupled) together to form a highly
available time reference; these two ETRs must be synchronous to each
other.  A unique ETR ID is assigned to each ETR in the installation,
and a unique ETR port number is assigned to each port of an ETR.  The
combination of ETR ID and ETR port number uniquely identifies an ETR
port in the installation, and is used by the control program running
on each connected CPC to identify link connection for problem
determination.

      More than one ETR network may exist in an installation.  Each
ETR network is assigned a unique ETR network ID.  The ETR network ID
is used to identify the synchronization source from which all
synchronized ETR signals are derived.

      Each CPC has at least two ports for availability; each CPC port
can be connected to an ETR.  At any time, ETR signals received from
one CPC port are used within the CPC for clock synchronization.
Automatic port selection is provided so that if the CPC port,
currently used, becomes not operational, the CPC can automatically
select ETR signals from another port without losing synchronization.
High availability can be achieved by using a coupled ETR and by
connecting each CPC port to a different ETR in the same network.
This typical ETR connection, as shown, does not have any single point
of failure.  The control program can verify this high-availability
connection by using ETR ID and ETR network ID.

      The ETR provides three signals at all ETR ports: ETR oscillator
signal, ETR data, and ETR on-time event (OTE).

      The ETR oscillator signal is used by each connected CPC to
derive the stepping signal to advance all TOD clocks in the system.

      The ETR data includes ETR time at next OTE, ETR network ID, ETR
ID, ETR port number, ETR status, and information for the conversion
between various standards.

      An ETR OTE occurs once every 1.048576 seconds and corresponds
to a carry out of bit position 32 of a TOD clock.

The ETR OTE is used in two ways:

1.  To start the stopped primary TOD clock in the connected CPC,

    and

2.  To test that the ETR and the primary TOD clock are running in
    synchronism.  If they are not in synchronism, an ETR-sync-check
    interruption condition is repo...