Re[2]: NTPsec reports excessive jitter from GPSD/KPPS SHM

[Nick Burkitt]

Hi Gary.

ntpshmmon is what tipped me off that PPS only appears to get one SHM unit.

gpsd command line:

gpsd -n /dev/pps0 /dev/ttyACM4

ntp configuration:

 # GPS Serial data reference (NTP0) 
refclock shm unit 1 refid GPS noselect 

 # GPS PPS reference (NTP1)
 refclock shm unit 0 minpoll 3 maxpoll 3 refid PPS prefer 

Output of ntpshmmon . Note SHM(0) and SHM(1), not SHM(2).

ntpshmmon: version 3.20

# Name Seen@ Clock Real L Prc

sample NTP0 1583778758.001081415 1583778757.999987360 1583778758.000000000 0 -20

sample NTP1 1583778758.085489797 1583778758.084407717 1583778758.000141035 0 -20

sample NTP0 1583778759.000212073 1583778758.999987443 1583778759.000000000 0 -20

sample NTP1 1583778759.092011896 1583778759.091448546 1583778759.000140814 0 -20

sample NTP0 1583778760.000063259 1583778759.999986945 1583778760.000000000 0 -20

sample NTP1 1583778760.086485810 1583778760.085459975 1583778760.000140593 0 -20

sample NTP0 1583778761.000370340 1583778760.999986648 1583778761.000000000 0 -20

sample NTP1 1583778761.081385024 1583778761.081222007 1583778761.000140373 0 -20

sample NTP0 1583778762.000288135 1583778761.999986620 1583778762.000000000 0 -20

sample NTP1 1583778762.088922000 1583778762.087842742 1583778762.000140152 0 -20

-Nick

------ Original Message ------

From: "Gary E. Miller" <address@hidden>

To: address@hidden

Sent: 3/9/2020 11:31:13 AM

Subject: Re: NTPsec reports excessive jitter from GPSD/KPPS SHM

Yo Nick!

 

On Mon, 09 Mar 2020 18:13:10 +0000

"Nick Burkitt" <address@hidden> wrote:

 

Although it appears that gpsd assigns only one shared memory unit for

PPS devices. So if I declare my PPS device before my GPS device on

the gpsd command line, I have to configure ntpd to use SHM(0) as the

PPS and SHM(1), not SHM(2), as the GPS.

 

Nope. SHM(0) as the PPS, and SHM(2) as the GPS.

 

Just run ntpshmmon to see it.

 

RGDS

GARY

---------------------------------------------------------------------------

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703

address@hidden Tel:+1 541 382 8588

 

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