Guardian Procedure Calls Reference Manual (G06.25+)

Guardian Procedure Calls (S)
Guardian Procedure Calls Reference Manual—522629-013
14-122
SETSYSTEMCLOCK Procedure
Stopping Clock Adjustment
•
If you call SETSYSTEMCLOCK with the mode parameter set to 8, the system
stops any ongoing adjustment.
•
If you call SETSYSTEMCLOCK twice in less than ten seconds, the system stops
any ongoing adjustment and sets the clock.
•
HP reserves the right to change, with proper customer notification, the
characteristics of system clock setting and adjustment. The only guaranteed
feature is that calling SETSYSTEMCLOCK twice in ten seconds causes the clock
to be set. The only exception is when the
mode parameter has the value 6. In this
case, the clock will not be set under any circumstances.
Types of Timestamps
•
A 48-bit timestamp is a quantity equal to the number of 10-millisecond units since
00:00, 31 December 1974. The 48-bit timestamp always represents local civil
time.
•
Procedures that work with the 48-bit timestamp are CONTIME, TIME, and
TIMESTAMP.
•
A 64-bit Julian timestamp is based on the Julian Date. It is a quantity equal to the
number of microseconds since January 1, 4713 B.C., 12:00 (noon) Greenwich
mean time (Julian proleptic calendar). This timestamp can represent either
Greenwich mean time, local standard time, or local civil time. There is no way to
examine a Julian timestamp and determine which of the three times it represents.
•
Procedures that work with the 64-bit Julian timestamp are COMPUTETIMESTAMP,
CONVERTTIMESTAMP, INTERPRETTIMESTAMP, JULIANTIMESTAMP, and
SETSYSTEMCLOCK.
•
All time and calendar units in this discussion are defined in The Astronomical
Almanac published annually by the U.S.þNaval Observatory and the Royal
Greenwich Observatory.
Timing and Processes
•
Process creation time is initialized by calling TIMESTAMP, which returns the local
civil time in centiseconds (0.01 second = 10 milliseconds) since midnight (00:00)
on 31 December 1974 in an array of three words. Only the two low-order words
are saved in the process control block (PCB); this is sufficient to make the
unnamed process ID unique.
•
Process timing uses 64-bit elapsed time counters with microsecond resolution;
these are not Julian timestamps either.
•
There is no way to generalize about internal timing using 64-bit Julian timestamps
or 48-bit timestamps. Each section of the operating system manages time using
the method most appropriate for its application.