[time-nuts] Clock project request from IEEE

[Mark Sims]

Lady Heather has a feature designed just for this application.  The TS keyboard command (and the /ts? command line options) allow setting the system clock from the time message sent by a GPS receiver (assuming the program has permission to set the clock).  This typically gets the system time set to under 50-100 msecs.

There are several issues that had to be overcome to make this work properly... the main one was characterizing and compensating for the delay / offset between when the GPS  time message arrives at the computer and the actual time encoded in the message.   I characterized the "time sync offset" for all the receivers that Heather supports and the program applies those default values.  You can also set the value manually (/tsx=) if your receiver / configuration / system / serial port does not match the default value.

The TS keyboard command sets the clock on demand.  The various /ts? command line options let you set the clock on a scheduled basis or whenever the system clock and GPS time diverge by a specified amount.  

The big disadvantage of Heather's clock setting algorithm is that the time set is a rather dumb "jamsync:" of the time... there is none of the smooth, monotonic clock adjustment that things like NTP do.   Jamming the time in can screw up file system time stamps, etc (hey! new file write looks like it occurred before an older file write, etc).  But, if you in a place without internet access it works quite well.  I develop Heather on a Windows XP box that is NEVER connected to the internet... the system clock drifts around a second per day.

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> This does have an application that I've recently experienced, manually
setting the time on a PC that's used for amateur radio digital (FT8)
communications which require the computer's clock to be accurate
within 1 second.