Re: NetBSD as an NTP stratum 1 server

[Greg Troxel <gdt%lexort.com@localhost>]

Brad Spencer <brad%anduin.eldar.org@localhost> writes:

>> There is actually support for PPS with USB devices that put the pps
>> signal on one of the modem pins, and I'm using it.  I think that I added
>> it a few years ago, and it was pretty easy.  However, there are two

I did, and it's been 9 years.

>> issues:
>>
>>   almost no USB GPS receivers bring PPS out on DCD.  I have a GR-601W or
>>   some model number like that, with a ublox 6, that was a special run
>>   that wired PPS to DCD inside.  If you have wired up a USB/serial chip
>>   and a GPS chip, then you may have this too.  But if you just bought a
>>   "gps mouse" or dongle, it is highly unlikely.
>>
>>   There is 1 ms of fuzz on timing.
>
> Oh, very nice to hear that and I was unaware that support existed.  My
> last test on this matter was with gpsd and it didn't seem to find the
> defines needed to make that work and my quick look at the source was not
> in the USB tty code so I missed seeing the support.

Sounds like you found it, but in case anybody else is looking:
  src/sys/dev/usb/ucom.c
  revision 1.106 from 2014-07-25

and the 1 ms fuzz is noted in ucom(4).

> The use of DCD in this manor is like a GPIO pin, but as you say, the USB
> fuzz may get in the way as the signal is transported via a USB packet.

AIUI, gpsd does not work with PPS on NetBSD at all because it is written
to the linux extension of the PPS API, not the RFC-specified version
that NetBSD implements.  These issues are about TIOCMWAIT not being
implemented in pps code in general, not about any particular pps
provider.

ntpd's pps code works with with the ucom pps, or at least it did pretty
recently.  (My ntp setup has decayed, likely due to other issues, not
this.)