[LinuxPPS] Recommendation / Re: Stats & architectures

[Remco den Besten]

In order to reduce uncertainties whether Rodolfo's PPS API works, I STRONGLY 
recommend
the following:

Use the ATOM (driver22) for PPS --in _conjunction with another driver_ which 
is
able to handle Rodolfo's PPS-API/kernel patch-- (i.e. Motorola Oncore 
(driver31) or
NMEA (driver20 with the patch from Udo) with ntpd-4.2.4p2).

Of course, prior to all doing this: follow the LinuxPPS-wiki.

Do NOT activate the PPS option for the ONCORE or NMEA driver (flag3 = 0), 
i.e. in ntp.conf :
#NMEA 4800 bps on ttyS1 no PPS enabled, low stratum because NMEA is used as 
'enabler'/dummy
server 127.127.20.1 prefer # <- necessary for the ATOM driver to lock on
fudge 127.127.20.1 time1 0.0 stratum 15 flag2 1 flag3 0 refid NMEA

but activate the ATOM driver instead:
#ATOM PPS on ttyS1 (falling edge flag2 1)
server 127.127.22.1
fudge 127.127.22.1 time1 0.0 flag2 1 flag3 1 stratum 0 refid PPS

Restart ntpd and after a while ntpd is locked onto the NMEA driver (mostly
after 4 cycles, i.e. with a reach of '17' (<- octal 1111) GPS_NMEA(1) gets a 
'*')
When the NMEA time is within (I thought) 500 ms of the 'real' time, the ATOM
driver will take over and a 'o' (i.e. oPPS(1) in this example) is visible 
when querying with 'ntpq -p'.
After that the PLL will converge to its value. You will always experience 
jitter and deviations,
depending upon the load of the system and/or temperature variations, etc. 
This a whole science
in itself (aka timekeeping ;-)

When you see no 'o', the PLL does not have a PPS lock. <- period ;-)

With no PPS lock you can not say anything about the quality, precision
or stability of the system / PPS-API.

First get an 'o', then worry later ;-)

>> > I'm still having tremendous problems trying to get PPS to
>> work properly on
>> > my new server..
>> >
>> > Two questions:
>> > In the present PPS implementation (V5.x), what should
>> ntptime show when PPS
>> > is in lock? On my system it has never shown anything other
>> than 'status 0x1
>> > (PLL)' where older PPS versions (on my previous system)
>> used to somewhat
>> > different info?
>>

*** SNIP***