Re: GPS Mac OS challenges

[Gary E. Miller]

Yo Marc!

On Fri, 10 Dec 2021 16:42:52 -1000
Marc Rosen <marc.rosen@me.com> wrote:

> clarification
> 
> this - I tried, doesnt work on the new OS
> 
> As root:
> Marcs-2020-MacBook-Pro-2:~ root#  ln -s /dev/cu.usbmodem1203 /dev/gps0
> ln: /dev/gps0: Operation not permitted

Ouch.

> I am running gpsd

Of course.

> I am running ntpd with a reference to the “127.127.28.0” magic
> numbers - I thought that allows ntpd to access the gpsd shared memory

Yes, but the newer syntax is clearer:

refclock shm unit 1 refid PPS minpoll 3 maxpoll 3 prefer
refclock shm unit 0 refid PTP minpoll 3 maxpoll 3


> time.apple,com is an ntp server correct?

I thought so, but no.  Easy to see that:

 # nmap  time.apple.com
Starting Nmap 7.92 ( https://nmap.org ) at 2021-12-10 18:48 PST
Nmap scan report for time.apple.com (17.253.24.125)
Host is up (0.052s latency).
Other addresses for time.apple.com (not scanned): 17.253.24.253 17.253.6.125 
17.253.20.125 17.253.20.253
rDNS record for 17.253.24.125: uschi5-ntp-001.aaplimg.com
All 1000 scanned ports on time.apple.com (17.253.24.125) are in ignored states.
Not shown: 1000 filtered tcp ports (no-response)

Nmap done: 1 IP address (1 host up) scanned in 53.89 seconds

For comparison, my pool server:

# nmap pi4.rellim.com
Starting Nmap 7.92 ( https://nmap.org ) at 2021-12-10 18:49 PST
Nmap scan report for pi4.rellim.com (204.17.205.24)
Host is up (0.0016s latency).
Other addresses for pi4.rellim.com (not scanned): 2001:470:e815::24
Not shown: 996 closed tcp ports (reset)
PORT    STATE SERVICE
22/tcp  open  ssh
80/tcp  open  http
111/tcp open  rpcbind
443/tcp open  https
MAC Address: B8:27:EB:0E:ED:29 (Raspberry Pi Foundation)

Nmap done: 1 IP address (1 host up) scanned in 0.19 seconds

> so apple’s time/date dialog
> references that to set the system time,

Yes.  But when?  How often?  I'm guessing only at startup.

> how will me running a local
> ntpd instance outcompete that ?

Good question.  If time set only at startup, then no problem.  BUt if
teim reset every so often, then they will fight.

> do I just shut down the mac’s timed
> process?

That would be my guess.

This says timed ix a PITA:

https://apple.stackexchange.com/questions/414088/macos-timed-wont-keep-accurate-time

> PPS:/dev/cu.usbmodem1203  cycle: 0, duration: 0 @ 0.000000000

As I expected, that say you have no PPS.

Otherwise, looks good.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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