[ntp:questions] Setting the COM port for the NMEA driver

Dave Hart davehart at gmail.com
Sat May 9 10:05:24 UTC 2009

> Does NTP even allow COM4?

I don't think so.  The unit numbers are limited to 0-3, I believe, but
I don't have any concept of why.  Windows never has a COM0:, so
arguably it was a poor choice to map unit number to com port number
without adding 1, but it's far too late to change that.  At the cost
of additional documentation complexity, ntpd could easily enough
interpret unit 0 as COM4:

Two solutions come to mind, either of which would probably work.
Somewhere in the registry there lurks a mapping, obviously named by
someone very young and self-impressed, known as the "COM port
database".  I got your database right here, buddy.  There's a tiny
little API used by serial port drivers to claim COM port numbers, but
I suspect you can ignore the API and fiddle the registry directly.

Quite possibly easiest would be to disable or renumber COM1:, COM2: or
COM3:.  I think there might even be an easy mousy way to choose the
COMx: assignment via device manager properties dialogs.  Try changing
an unused 1-3 to a higher port and your USB adapter will likely claim
the lowest-numbered available port next boot.

Good luck,
Dave Hart

P.S.  I predict you'd be able to get better time over the internet
than over USB, but I'd love to be wrong.   But then, you might end up
the first to have tried PPS over serial USB and get much better
results than your predecessors.  Thanks for taking the time to
investigate this.

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