Re: [chrony-users] Setting up Chrony with PPS

[Roel Schroeven]

Deven Hickingbotham schreef op 2016-04-11 22:10:

Yes, but I didn't expect that it would affect chrony.  The update rate
was increased from 1 per second to 10 time per second (since this didn't 
affect the PPS signal, I didn't expect it to impact chrony).


Changing the update rate back to 1 per second corrected the issue, but I
need an update rate of at least 5 per second (preferably 10).
  
Is the GPS connected with a serial link? What baudrate? Default for NMEA 
is 4800 bps AFAIK, but if I'm reading Adafruit's website correctly your 
Adafruit Ultimate GPS uses 9600 bps by default. Even that may not be 
enough for 10 position updates per second. Maybe the GPS simply has 
trouble sending all data in the available time.


Can you try increasing the baudrate of the serial connection? See 
https://learn.adafruit.com/adafruit-ultimate-gps/faq#faq-4


HTH

Best regards,
Roel

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Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh]

On Tue, 12 Apr 2016, Deven Hickingbotham wrote:


On 4/11/2016 10:41 PM, Miroslav Lichvar wrote:

That probably depends on the FW of the GPS. If with one update per
second the NMEA messages were only 0.1 second late, with 10 updates
per second that delay wouldn't have to change, it would still fit
between updates. But if it's 0.5 second late, that can't work with 10
updates per second.

I think you just need to change the offset of the SHM refclock to 0.1
second. The delay can stay as it was.


Setting offset to 0.1 works for 10, 5, 4, 3, and 2 updates per second.

Setting offset to 0.5 works for updates every 1 and 2.5 seconds.  It does not 
work for updates every 5 seconds.


If a future version of chrony could support a wide range of gps update rates 
without having to modify chrony.conf, that would be appreciated.


?? why the demand not to modify chrony.conf? It is there precisely to put in
configuration information.

Your update frequency is something you set once, and a bit of effort to get it
right is a good idea. It is somewhat hard for the program itself to know how
far off the time is since it is the only thing that tells it what the time is.



Thanks for the support, it has been very helpful and timely!

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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

On 4/12/2016 12:29 PM, Roel Schroeven wrote:

Is the GPS connected with a serial link? What baudrate? Default for NMEA
is 4800 bps AFAIK, but if I'm reading Adafruit's website correctly your
Adafruit Ultimate GPS uses 9600 bps by default. Even that may not be
enough for 10 position updates per second. Maybe the GPS simply has
trouble sending all data in the available time.

Can you try increasing the baudrate of the serial connection? See
https://learn.adafruit.com/adafruit-ultimate-gps/faq#faq-4



Yes, serial.  Baud rate is set to 115200.

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Re: [chrony-users] Setting up Chrony with PPS

[Miroslav Lichvar]

On Mon, Apr 11, 2016 at 01:10:30PM -0700, Deven Hickingbotham wrote:
> 
> On 4/10/2016 11:30 PM, Miroslav Lichvar wrote:
> >Hm, did the configuration of the GPS change? Maybe it's giving fewer
> 
> Yes, but I didn't expect that it would affect chrony.  The update rate
> was increased from 1 per second to 10 time per second (since this didn't
> affect the PPS signal, I didn't expect it to impact chrony).
> 
> Changing the update rate back to 1 per second corrected the issue, but I
> need an update rate of at least 5 per second (preferably 10).
> 
> Would it be correct to assume that different update rates require
> different chrony offsets and delays?  And if so, what values should I try?

That probably depends on the FW of the GPS. If with one update per
second the NMEA messages were only 0.1 second late, with 10 updates
per second that delay wouldn't have to change, it would still fit
between updates. But if it's 0.5 second late, that can't work with 10
updates per second.

I think you just need to change the offset of the SHM refclock to 0.1
second. The delay can stay as it was.

-- 
Miroslav Lichvar

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Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh]

On Mon, 11 Apr 2016, Deven Hickingbotham wrote:


On 4/11/2016 2:26 PM, Bill Unruh wrote:

So please tell us what it is you are trying to do that makes you think you
want more frequency updates.


The faster update rate is not to get GPS time more frequently, but to get GPS 
location data more frequently.  I'm working on an auto racing app where the 
car can be moving at 250 feet per second, so an update every second is not 
very accurate for my needs.


CAn you not tell the gps to deliver time and location at rates which are
independent of each other? And are you sure that the gps can really update the
position at 10 times per second? There are quite a lot of calculations and
measurements that need to be done to update the position. Is you receiver
capable of doing it. (Just because it says it does something 10 times per sec
does not mean it delivers anything meaningful that quickly).



Deven

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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

On 4/10/2016 11:30 PM, Miroslav Lichvar wrote:

Hm, did the configuration of the GPS change? Maybe it's giving fewer
NMEA sentences than before? It looks like the NMEA samples are now
~400 ms off from the expected offset and PPS can't lock to them.
You could try changing the SHM offset to 0.1 and maybe increase the
delay to 0.6 or so, but I'm not sure if that will be enough if the
NMEA offset is changing so much over time.



Yes, but I didn't expect that it would affect chrony.  The update rate
was increased from 1 per second to 10 time per second (since this didn't 
affect the PPS signal, I didn't expect it to impact chrony).


Changing the update rate back to 1 per second corrected the issue, but I
need an update rate of at least 5 per second (preferably 10).

Would it be correct to assume that different update rates require
different chrony offsets and delays?  And if so, what values should I try?

Thanks,

Deven



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Re: [chrony-users] Setting up Chrony with PPS

[Bryan Christianson]

> On 19/02/2016, at 1:08 PM, Deven Hickingbotham  wrote:
> 
> Now 10 minutes after restarting chronyc sources outputs:
> 
> pi@gps ~/SystemFiles $ chronyc sources
> 210 Number of sources = 7
> MS Name/IP address  Stratum Poll LastRx Last sample
> ===
> ^~ tock.usshc.com   16 41   -263ms[ -263ms] +/-   61ms
> ^~ pacific.latt.net 36 21   -323ms[ -323ms] +/-   82ms
> ^x leeloo.scurvynet.com 26 13   -317ms[ -317ms] +/-  127ms
> ^~ repos.lax-noc.com26 22   -326ms[ -326ms] +/-   63ms
> #x SHM0 04 21+18ms[  +18ms] +/- 3102us
> #? PPS  0410y +0ns[   +0ns] +/-0ns
> #? SOCK 0410y +0ns[   +0ns] +/-0ns
> 
> 
> So SHM0   does show up.  Still question the use of chrony.ttyAMA0.sock?
> 
> Deven
> 


OK _ are you stopping gpsd, restarting chronyd then restarting gpsd? Order 
matters (well it used to anyway)


Bryan Christianson
br...@whatroute.net




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Re: [chrony-users] Setting up Chrony with PPS

[Bryan Christianson]

> On 19/02/2016, at 12:07 PM, Tomalak Geret'kal  wrote:
> 
> On 18/02/2016 22:48, Deven Hickingbotham wrote:
>> 
>>> $cat /sys/class/pps/pps0/assert 
>>> 1455831692.018636856#178 
>>> 
>>> Are you seeing those? 
>>> 
>> 
>> Yes, but just one timestamp per execution: 
>> 
>> pi@gps ~ $ cat /sys/class/pps/pps0/assert 
>> 1455835119.289108505#4272 
>> pi@gps ~ $ cat /sys/class/pps/pps0/assert 
>> 1455835154.690359907#4305 
>> pi@gps ~ $ cat /sys/class/pps/pps0/assert 
>> 1455835157.936493770#4308 
>> pi@gps ~ $ cat /sys/class/pps/pps0/assert 
>> 1455835160.102904599#4310 
>> 
> 
> Okay so your PPS looks fine.
> 
> I think what's happening (and I'm half guessing but I did the following in 
> the past to solve the same problem) is that you have two separate refclocks. 
> One is your GPS NMEA (which is working), and the other is your PPS source ... 
> which is only providing timing, not time.
> 
> I believe you need to make it so that the PPS refclock is treated as a sort 
> of extension of the GPS refclock, then prevent the GPS refclock from being 
> selected on its own:
> 
> refclock SHM 0 refid GPS precision 1e-1 offset 0. delay 0.2 noselect
> refclock SOCK /var/run/chrony.ttyAMA0.sock refid PPS lock GPS
> 
> I'm not sure why you see "PP" in the "chronyc sources" output - double-check 
> your file on disk for dodgy line endings perhaps? Bit of a concern if the 
> trailing "S" now gets truncated in my example above.
> 
> Anyway, give that a try.
> 
> Cheers
> Tom

I have this config working on a RP 2 - different PPP device but substituting 
your device for mine and adjusting the offsets to suit your device may work. I 
got this config from the gpsd web site

# SHM0 from gpsd is the NEMA data at 4800bps, so is not very accurate
refclock SHM 0  precision 1e-1 offset -0.135 delay 0.5 refid NEMA

# SHM1 from gpsd (if present) is from the kernel PPS_LDISC
# module.  It includes PPS and will be accurate to a few ns
refclock SHM 1 offset 0.00135 delay 0.1 refid PPS

# SOCK protocol also includes PPS data and 
# it also provides time within a few ns
refclock SOCK /var/run/chrony.ttyUSB0.sock offset 0.00135 delay 0.0 refid SOCK

Bryan Christianson
br...@whatroute.net




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Re: [chrony-users] Setting up Chrony with PPS

[Yan Seiner]

On 2/18/2016 8:19 PM, Deven Hickingbotham wrote:


GPS is an Adafruit Ultimate GPS Hat on a Raspberry Pi 2 B.  I have two 
identical units and have had PPS working with ntp.


Is it possible to bring the PPS signal in on a serial port?  I'm doing 
something similar but with different hardware; using an internal TTL 
level serial port rather than GPIO.  I had no luck with GPIO.  Also, 
I've found that it's best to have a time delay before starting gpsd:


root@AP1:~# cat /etc/rc.local
$( sleep 60 ; /etc/init.d/gpsd start ) &
exit 0

That 60 second delay apparently gives enough time to chrony to do 
whatever it needs to do.  Make sure you delete SXXgpsd from rc.d if 
that's how it's starting.


root@AP1:~# chronyc sources
210 Number of sources = 6
MS Name/IP address Stratum Poll Reach LastRx Last sample
===
#- NEMA  0   4   37711   +141ms[ +141ms] 
+/-  251ms
#* PPS   0   4   377 9   +403us[ +404us] 
+/-   50ms
^+ vexx.wtfismyip.com2   6   37713   +317us[ +320us] 
+/-   81ms
^- ntp2.tranzeo.com  2   6   37710  -2895us[-2893us] 
+/-  565ms
^? mirror3.rafal.ca  0   6 0   10y +0ns[   +0ns] 
+/-0ns
^+ zero.gotroot.ca   2   6   377 9  -1172us[-1171us] 
+/-   64ms



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Re: [chrony-users] Setting up Chrony with PPS

[Tomalak Geret'kal]

On 19/02/2016 03:08, Bryan Christianson wrote:
My understanding is that chrony.ttyAMA0.sock is a socket 
created by chronyd and listened to by chronyd When gpsd 
starts, it checks to see if the socket exists and writes 
the PPS data to it.
Isn't that backwards? How would gpsd know what socket to 
write to?
Generally the model is the writer (which doesn't know what 
wants to receive) creates the file and the receiver (which 
knows what it wants to receive) opens it.

We can see that here by the presence of gpsd.sock.
Right?

Tom

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Re: [chrony-users] Setting up Chrony with PPS

[Tomalak Geret'kal]

On 18/02/2016 22:48, Deven Hickingbotham wrote:



$cat /sys/class/pps/pps0/assert
1455831692.018636856#178

Are you seeing those?



Yes, but just one timestamp per execution:

pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835119.289108505#4272
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835154.690359907#4305
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835157.936493770#4308
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835160.102904599#4310



Okay so your PPS looks fine.

I think what's happening (and I'm half guessing but I did 
the following in the past to solve the same problem) is that 
you have two separate refclocks. One is your GPS NMEA (which 
is working), and the other is your PPS source ... which is 
only providing /timing/, not /time/.


I believe you need to make it so that the PPS refclock is 
treated as a sort of extension of the GPS refclock, then 
prevent the GPS refclock from being selected on its own:


refclock SHM 0 refid GPS precision 1e-1 offset 0. delay 
0.2 *noselect*

refclock SOCK /var/run/chrony.ttyAMA0.sock refid PPS *lock GPS*

I'm not sure why you see "PP" in the "chronyc sources" 
output - double-check your file on disk for dodgy line 
endings perhaps? Bit of a concern if the trailing "S" now 
gets truncated in my example above.


Anyway, give that a try.

Cheers
Tom

Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh]

William G. Unruh   |  Canadian Institute for| Tel: +1(604)822-3273
Physics  | Advanced Research  | Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology | un...@physics.ubc.ca
Canada V6T 1Z1 |  and Gravity   |  www.theory.physics.ubc.ca/

On Thu, 18 Feb 2016, Deven Hickingbotham wrote:



On 2/18/2016 6:57 PM, Bill Unruh wrote:

Is this more in line with what you expected?


Nope. Those are huge uncertainties for network timing. 134ms uncertainty
corresponds to light travel time around the earth uncertainty. I would
expect
more like +- 100 microseconds, not milliseconds.

What is your network link?


I have cable network.  Ping 41ms, 20mb downloads speed, 5mp upload.



Should still be a lot better than what you are getting. I also have cable
(Shaw cable in Vancouver) 
^* info.physics.ubc.ca   1   6   37757   -422us[ -465us] +/- 5975us


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Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh]

William G. Unruh   |  Canadian Institute for| Tel: +1(604)822-3273
Physics  | Advanced Research  | Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology | un...@physics.ubc.ca
Canada V6T 1Z1 |  and Gravity   |  www.theory.physics.ubc.ca/

On Thu, 18 Feb 2016, Deven Hickingbotham wrote:

First off, thanks for all of the responses!  I'm testing your suggestions as 
fast as I can and if I apologize if  I don't directly reply to a suggestion.




Does /var/run/chrony.ttyAMA0.sock exist? If not, then it is hard to read
from
it. Your gpsd does not seem to be writing to SHM0



Yes, it does exist:

pi@gps /var/run $ ls -l *.sock
srwxr-xr-x 1 root root 0 Feb 18 16:23 chrony.ttyAMA0.sock
srw-rw 1 root root 0 Feb 18 15:43 dhcpcd.sock
srw-rw-rw- 1 root root 0 Feb 18 15:43 dhcpcd.unpriv.sock
srwxr-xr-x 1 root root 0 Feb 18 16:23 gpsd.sock


OK, not sure what it does 


But I don't think it existed before I configured chrony.


I suspect it is a socket that chrony listens to, but there needs to be
something that actually writes to that socket as well. 
But I have never used sockets on chrony so have no idea.






I am also concerned that your outside clocks are way off ( hundreds of ms )
and have HUGE variances -- the network, unless you are using smoke
signals for
your network, should not be out by a hundred ms. Mind you telling your
system
that  your SHM0  is out by 135ms is probably all wrong, and is part of the
problem.

So, I would first suggest that you get rid of the nmea, and just use the
external clocks as your reference. and get PPS working. Then  you can
try to
get nmea working.  One thing at a time.




After removing the refclock references from chrony.conf I get:

pi@gps ~/SystemFiles $ chronyc sources
210 Number of sources = 4
MS Name/IP address Stratum Poll LastRx Last sample
==
^+ gopher.fart.website 37 43+16ms[  +14ms] +/-   89ms
^? mirror  37 41+17ms[  +17ms] +/-  134ms
^~ com1243.eecs.utk.edu   166 59+71ms[  +55ms] +/-   55ms
^* tock.usshc.com  16 59+15ms[ -696us] +/-  122ms

Is this more in line with what you expected?


Nope. Those are huge uncertainties for network timing. 134ms uncertainty
corresponds to light travel time around the earth uncertainty. I would expect
more like +- 100 microseconds, not milliseconds.

What is your network link?




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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

Bill,

On 2/18/2016 4:06 PM, Bill Unruh wrote:

pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835119.289108505#4272


Yes, as should be, assuming that it was about 33 sec between the one
above and
below, and then about 3 sec. However I am worried that you are getting
such differences in ms. What GPS
device are you using? Are you sure its PPS is working? Or is your computer
really that far off in its clock rate?


GPS is an Adafruit Ultimate GPS Hat on a Raspberry Pi 2 B.  I have two 
identical units and have had PPS working with ntp.


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Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh]

On Thu, 18 Feb 2016, Deven Hickingbotham wrote:


On 2/18/2016 4:12 PM, Bryan Christianson wrote:
OK _ are you stopping gpsd, restarting chronyd then restarting gpsd? Order 
matters (well it used to anyway)


Yes, I did that.  No change in the chronyc sources output.  GPS apps like 
cgps -s work.


How can I tell what order the services load during startup?

--



You can start them and stop them while it is running. 
killall chronyd

killall gpsd

I do not know how what  you are using starts them up, or whether your system
uses systemd or init. 
service  gpsd start

service  chronyd start

might work.




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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

First off, thanks for all of the responses!  I'm testing your 
suggestions as fast as I can and if I apologize if  I don't directly 
reply to a suggestion.




Does /var/run/chrony.ttyAMA0.sock exist? If not, then it is hard to read
from
it. Your gpsd does not seem to be writing to SHM0



Yes, it does exist:

pi@gps /var/run $ ls -l *.sock
srwxr-xr-x 1 root root 0 Feb 18 16:23 chrony.ttyAMA0.sock
srw-rw 1 root root 0 Feb 18 15:43 dhcpcd.sock
srw-rw-rw- 1 root root 0 Feb 18 15:43 dhcpcd.unpriv.sock
srwxr-xr-x 1 root root 0 Feb 18 16:23 gpsd.sock

But I don't think it existed before I configured chrony.


I am also concerned that your outside clocks are way off ( hundreds of ms )
and have HUGE variances -- the network, unless you are using smoke
signals for
your network, should not be out by a hundred ms. Mind you telling your
system
that  your SHM0  is out by 135ms is probably all wrong, and is part of the
problem.

So, I would first suggest that you get rid of the nmea, and just use the
external clocks as your reference. and get PPS working. Then  you can
try to
get nmea working.  One thing at a time.




After removing the refclock references from chrony.conf I get:

pi@gps ~/SystemFiles $ chronyc sources
210 Number of sources = 4
MS Name/IP address Stratum Poll LastRx Last sample
==
^+ gopher.fart.website 37 43+16ms[  +14ms] +/-   89ms
^? mirror  37 41+17ms[  +17ms] +/-  134ms
^~ com1243.eecs.utk.edu   166 59+71ms[  +55ms] +/-   55ms
^* tock.usshc.com  16 59+15ms[ -696us] +/-  122ms

Is this more in line with what you expected?

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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

Bryan,

I changed chrony.conf to include:

refclock SHM 0  precision 1e-1 offset -0.135 delay 0.5 refid NEMA
refclock SHM 1 offset 0.00135 delay 0.1 refid PPS
refclock SOCK /var/run/chrony.ttyAMA0.sock offset 0.00135 delay 0.0 
refid SOCK


Now 10 minutes after restarting chronyc sources outputs:

pi@gps ~/SystemFiles $ chronyc sources
210 Number of sources = 7
MS Name/IP address  Stratum Poll LastRx Last sample
===
^~ tock.usshc.com   16 41   -263ms[ -263ms] +/-   61ms
^~ pacific.latt.net 36 21   -323ms[ -323ms] +/-   82ms
^x leeloo.scurvynet.com 26 13   -317ms[ -317ms] +/-  127ms
^~ repos.lax-noc.com26 22   -326ms[ -326ms] +/-   63ms
#x SHM0 04 21+18ms[  +18ms] +/- 3102us
#? PPS  0410y +0ns[   +0ns] +/-0ns
#? SOCK 0410y +0ns[   +0ns] +/-0ns


So SHM0 does show up.  Still question the use of chrony.ttyAMA0.sock?

Deven



On 2/18/2016 3:23 PM, Bryan Christianson wrote:

I have this config working on a RP 2 - different PPP device but substituting 
your device for mine and adjusting the offsets to suit your device may work. I 
got this config from the gpsd web site

# SHM0 from gpsd is the NEMA data at 4800bps, so is not very accurate
refclock SHM 0  precision 1e-1 offset -0.135 delay 0.5 refid NEMA

# SHM1 from gpsd (if present) is from the kernel PPS_LDISC
# module.  It includes PPS and will be accurate to a few ns
refclock SHM 1 offset 0.00135 delay 0.1 refid PPS

# SOCK protocol also includes PPS data and
# it also provides time within a few ns
refclock SOCK /var/run/chrony.ttyUSB0.sock offset 0.00135 delay 0.0 refid SOCK


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Re: [chrony-users] Setting up Chrony with PPS

[Bill Unruh]

William G. Unruh   |  Canadian Institute for| Tel: +1(604)822-3273
Physics  | Advanced Research  | Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology | un...@physics.ubc.ca
Canada V6T 1Z1 |  and Gravity   |  www.theory.physics.ubc.ca/

On Thu, 18 Feb 2016, Deven Hickingbotham wrote:


Rob,

Thanks for replying.

A little more info: my system is a Raspberry Pi 2 B.  I have been able to get 
ntp to work with pps via GPIO pin 4.  Had to recompile ntp to activate the 
pps support.


Don't let the above fool you into thinking I know what I am doing.  I have 
some level of expertise with programming, but system level Linux stuff is a 
mystery to me.  IOW, real clear step by step instructions are greatly 
appreciated!



If either module is being loaded, you should see a device (e.g. pps0) in
/sys/class/pps. If your GPS has a lock and the pps kernel module is
configured properly, you should see timestamps updating every second, e.g.



Yes, the /sys/class/pps/pps0 path exists and contains these files: subsystem 
(folder), assert, clear, dev, echo, mode, name, path, and uevent.



$cat /sys/class/pps/pps0/assert
1455831692.018636856#178

Are you seeing those?



Yes, but just one timestamp per execution:

pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835119.289108505#4272


Yes, as should be, assuming that it was about 33 sec between the one above and
below, and then about 3 sec. 
However I am worried that you are getting such differences in ms. What GPS

device are you using? Are you sure its PPS is working? Or is your computer
really that far off in its clock rate?



pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835154.690359907#4305
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835157.936493770#4308
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835160.102904599#4310


Have a look at the clear line to see if it is more regular (the ms should be
more or less the same 


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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

Tom,



refclock SHM 0 refid GPS precision 1e-1 offset 0. delay 0.2 noselect
refclock SOCK /var/run/chrony.ttyAMA0.sock refid PPS lock GPS



I made the above changes, restarted chrony, waited 10 minutes and:

pi@gps ~/SystemFiles $ chronyc sources
210 Number of sources = 6
MS Name/IP address   Stratum Poll LastRx Last sample

^~ 1.time.dbsinet.com26 25  +2169ms[+2169ms] +/-80ms
^~ nist.netservicesgroup.com 16  7  +2168ms[+2168ms] +/-50ms
^~ pacific.latt.net  36  5  +2169ms[+2169ms] +/-77ms
^~ clock.trit.net26  3  +2163ms[+2163ms] +/-28ms
#? GPS   0410y +0ns[   +0ns] +/- 0ns
#? PPS   0410y +0ns[   +0ns] +/- 0ns

This did fix PPS in that it now appears as 'PPS' and not 'PP'.

I'm beginning to think that the reference to chrony.ttyAMA0.sock may not 
work for three reasons:  isn't that serial access and I need GPIO?; 
LastRx indicates no connection; and this looks like it may be messing up 
gpsd as it uses ttyAMA0 as a source.


Deven


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Re: [chrony-users] Setting up Chrony with PPS

[Deven Hickingbotham]

Rob,

Thanks for replying.

A little more info: my system is a Raspberry Pi 2 B.  I have been able 
to get ntp to work with pps via GPIO pin 4.  Had to recompile ntp to 
activate the pps support.


Don't let the above fool you into thinking I know what I am doing.  I 
have some level of expertise with programming, but system level Linux 
stuff is a mystery to me.  IOW, real clear step by step instructions are 
greatly appreciated!



If either module is being loaded, you should see a device (e.g. pps0) in
/sys/class/pps. If your GPS has a lock and the pps kernel module is
configured properly, you should see timestamps updating every second, e.g.



Yes, the /sys/class/pps/pps0 path exists and contains these files: 
subsystem (folder), assert, clear, dev, echo, mode, name, path, and uevent.



$cat /sys/class/pps/pps0/assert
1455831692.018636856#178

Are you seeing those?



Yes, but just one timestamp per execution:

pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835119.289108505#4272
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835154.690359907#4305
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835157.936493770#4308
pi@gps ~ $ cat /sys/class/pps/pps0/assert
1455835160.102904599#4310

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