Browse Prior Art Database

Distribution and Synchronization of Time Data for Flexible Subsystem Access

IP.com Disclosure Number: IPCOM000119016D
Original Publication Date: 1997-Oct-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Hamilton II, RA: AUTHOR [+4]

Abstract

Disclosed is a method for distributing Time-of-Day data throughout a computer system, for the purpose of maximizing system flexibility and time data access.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Distribution and Synchronization of Time Data for Flexible Subsystem
Access

      Disclosed is a method for distributing Time-of-Day data
throughout a computer system, for the purpose of maximizing system
flexibility and time data access.

      Note: for this disclosure, the term "Time-of-Day" (TOD) refers
to an internal clock used for marking time within a computer system.

      Within a computer system, it is often desirable to allow
disparate and physically-removed components to access the timestamp,
which is derived from the TOD value.  These components may be
hardware, software, or firmware in nature, and may use the TOD for a
variety of reasons.  Germane examples of such usage include setting
up a timed-power-on function for the overall computer, or the
inclusion of a timestamp in firmware error reports for subsequent
problem diagnosis.  A fundamental problem is that the TOD may be
accessible only by the Operating System (OS) and a small subset of
the components which need such time data.  As system complexity
increases, this limited accessibility creates functional lapses,
where subsystems which might use time information cannot gain access
to it.  This disclosure will discuss a physical mechanism and
innovative methodology for distributing synchronized TOD information
within a Common Hardware Reference Platform (CHRP) system, resulting
in greater availability of the data and a corresponding increase in
functionality for the computer system as a whole.

      The approach taken on the RS/6000* Model S70 has been to
utilize a redundant TOD clock to increase timestamp availability.
This second clock is maintained in a physically-remote location from
the first, and a path and methodology have been established to permit
synchronization and distribution of the data.  Reference the Figure
for the example embodiment.  The actual distribution is achieved
through the following procedure, subject to the CHRP constraints
mentioned below.  Note that the Service Processor, in this
configuration, does not  have access to the System (primary) TOD
while the system is running.
  1.  Upon power-on, the Service Processor checks the System
       TOD and performs a resynchronization of its own TOD,
       ensuring that they reflect the same time value.  This
       resynchronization occurs before the boot firmware is
       loaded, which is the only time that the Service Processor
       has access to the System TOD.
  2.  The system boots, and the Service Processor is able to
       provide timestam...