Re: Automatic time setting using NIST

[Vern Hamberg <vhamberg@xxxxxxxxxxxxxxxxxxxxxxxxx>]

The hardware clock is what you called the system clock. CHGSYSVAL changes 
the hardware clock. The SNTP client from ConsultLine changes the hardware 
clock. I suppose one problem with this is, history log entries, job start 
times, etc., are based on the hardware clock. Changing this back and forth 
can have odd effects, I believe. In extreme cases, time-dependent products 
like ROBOT and the built-in job scheduler may miss a scheduled job.

The software clock is related to Unix-style functions, and the SNTP 
"server" that is now part of the system sets this value.

Here's the text from IBM on:

Software Clock APIs
The Software Clock APIs are:

- adjtime() (Adjust software clock) makes small adjustments to the software 
clock, either advancing or retarding it by the time specified in the delta 
parameter.

- gettimeofday() (Get current software clock time) retrieves the 
software-clock-based system time and places it in the timeval structure 
pointed to by tp.

- settimeofday() (Set current software clock time) sets the software clock 
to the time contained in the timeval structure pointed to by tp.

Note: These functions use header (include) files from the library QSYSINC, 
which is optionally installable. Make sure QSYSINC is installed on your 
system before using any of the functions. See for the file and member name 
of each header file.

The Software Clock is a system facility that determines the current 
Universal Coordinated Time (UTC) in seconds and microseconds since 1 
January 1970, 00:00:00 (epoch-1970), and allows for time zone and daylight 
savings time information to be stored and retrieved. The current time is 
determined by keeping an internal 'time-delta', which is an offset from the 
machine clock (accessible by the mattod() API). When gettimeofday() is 
called to retrieve the software clock time, the time returned is calculated 
by taking the current machine time, subtracting the QUTCOFFSET system 
value, then adding the internal time-delta.

Calling the settimeofday() API sets or changes the time-delta (and 
optionally the time zone and the daylight savings time information), but 
does not affect the machine clock or the QUTCOFFSET system value. The 
adjtime() API slowly changes the time-delta, but does not affect the 
machine clock either. Adjustments are made at a rate of approximately 1 
second of adjustment for every 100 seconds of elapsed time.

Most system components do not base their timestamps on the software clock, 
but use the machine clock instead.
================================================================================
HTH

Vern

At 10:35 AM 10/14/2003 -0500, you wrote:
> What is the difference between the "hardware clock" and the "software
> clock"?  Which does CHGSYSVAL change?
>
>
> Jeff Carey
> Technical Specialist
> iSeries Technology