Guardian Procedure Calls Reference Manual (G06.25+)

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Guardian Procedure Calls (T-V)

Guardian Procedure Calls Reference Manual—522629-013

15-13

TIMESTAMP Procedure

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.

•

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.

•

The RCLK instruction ($READCLOCK in TAL) is another source of timestamps. It

returns a 64-bit timestamp representing the local civil time in microseconds since

midnight (00:00) on 31 December 1974. Note that this is not a Julian timestamp.

•

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.

•

All time and calendar units in this discussion are defined in The Astronomical

Almanac published annually by the U.S. Naval Observatory and the Royal

Greenwich Observatory.

Example

CALL TIMESTAMP ( TIMESTAMP^BUF );

Related Programming Manual

For programming information about the TIMESTAMP utility procedure, refer to the

Guardian Programmer’s Guide.