[LinuxPPS] kernel 2.6.32 - ntpd-4.2.6 linuxpps experiences

[Remco dB]

Hello all, 

Having been an early LinuxPPS adaptor, it has been quiet for a while from this 
side. 

Today I decided to upgrade my kernel from 2.6.27.6 to 2.6.32 and had to figure 
out 'how on earth did I manage(d) to get LinuxPPS running after a kernel 
upgrade?'.

After downloading kernel 2.6.32, I applied the ntp-pps-v2.6.32-rc8.diff patch, 
compiled the kernel, and rebooted.

I followed the symlink circus (see LinuxPPS installation Wiki) as usual but 
when compiling the contents of the linux/Documentation/pps directory I got 
errors and did not pay much attention to it.

Before patching linux-utils with the ldattach patch, I tried my good old
ttyctrl -X -s 18 /dev/ttyS0 & , which worked, as could be determined with
watch -n1 cat /sys/class/pps/pps0/{clear,assert}.
(Can anyone tell me where the number 18 origins from??)

From my remembrance it was necessary to compile a new ntpd after a kernel 
upgrade, so this was the intuitive way to go forward. 

I discovered that the NANO option in timex.h is inserted as of kernel 2.6.30.
However, for whatever reason with this timex.h ntpd failed to compile. So I 
used the 'old' timex.h nano patch from the mid 2008s instead, which worked. 

I used ntpd-4.2.5-p113 and after starting the freshly compiled ntpd I could 
not find my Oncore (driver 30) in the peers list (ntpq -p). 

Having more things to do today than being busy with LinuxPPS I downloaded the 
latest stable ntp version (4.2.6) and compiled it. 

With this version GPS_ONCORE(0) appeared in the peers list, but no 
synchronization could be detected. 

Knowing that I had PPS stamps, I tried the ATOM driver (driver 22), and used a 
preferred time source from my local network. After a while ntpd-4.2.6 synced 
to my PPS signal ... WITH the ppsfreq, and ppstime bits set (!). 

remco at helium > ntpdc -c kern
pll offset:           -6.82e-07 s
pll frequency:        17.942 ppm
maximum error:        0.007736 s
estimated error:      0 s
status:               2007  pll ppsfreq ppstime nano
pll time constant:    4
precision:            1e-09 s
frequency tolerance:  500 ppm

remco at helium > ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
oPPS(0)          .PPS.            0 l   13   16  377    0.000   -0.001   0.002
*freebsd         .GPS.            1 u   63   64  377    0.211    0.000   0.012
+lithium         .DCFa.           1 u   42   64  377    0.157   -0.655   0.110
+ptbtime1.ptb.de .PTB.            1 u   46   64  377   49.874    0.244   0.198

The stability seems to be better than with the 2001 status (pll , nano) but I 
wonder why the Oncore driver fails to work. 

Remco