[LinuxPPS] ntp: add hardpps implementation

[Udo van den Heuvel]

On 2010-10-10 17:19, Remco dB wrote:
> OK, 
> 
> I applied the latest Alex-patch on kernel-2.6.34 and got 'it' working 
> according to Udo's howto on the PPS wiki. 
> 
> Interestingly, when I perform a ntpdc -c kern <LinuxPPS machine with hardpps> 
> the PLL offset remains rock solid 0 sec. 
> Status now is 0x2107 instead of 0x2007 or 0x2001.
> 
> However, when I do a ntpq -p the offset remains .. rock solid 127 us. 
> When I do not use hardpps the system behaves more 'normal' and displays
> with a ntpq -p query to an offset of +/- 0.001 on the same system.

Hmmm:
[root at epia tor]# ntptime
ntp_gettime() returns code 0 (OK)
  time d05c5924.15be7f24  Sun, Oct 10 2010 17:24:20.084, (.084938024),
  maximum error 7239 us, estimated error 4 us, TAI offset 0
ntp_adjtime() returns code 0 (OK)
  modes 0x0 (),
  offset 0.000 us, frequency 3.669 ppm, interval 256 s,
  maximum error 7239 us, estimated error 4 us,
  status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
  time constant 4, precision 0.001 us, tolerance 500 ppm,
  pps frequency 3.662 ppm, stability 0.013 ppm, jitter 4.543 us,
  intervals 695, jitter exceeded 8, stability exceeded 0, errors 0.
[root at epia tor]# ntpq -pn
     remote           refid      st t when poll reach   delay   offset
jitter
==============================================================================
o127.127.20.0    .GPS.            0 l    6   16  377    0.000    0.006
 0.002
+194.109.22.18   193.79.237.14    2 u   15   64  377   21.115   -3.260
23.025
+194.109.20.18   193.79.237.14    2 u   55   64  377   21.114   -3.681
34.720
+193.67.79.202   .PPS.            1 u   24   64  377   21.120   -2.905
31.162
+193.79.237.14   .PPS.            1 u   66   64  377   21.108   -3.685
31.010
*83.163.219.98   .DCFa.           1 u   63   64  377   41.072   -9.059
 6.893
 134.221.205.12  .FLY.            1 u  169 1024    0    0.000    0.000
 0.000

Any conclusions yet? (VIA Epia LT10000)

> PLL freq without hardpps is 157 ppm and with hardpps 30 ppm.

http://pindarots.xs4all.nl/mrtg/ntppll.html shows a lower pll number.

> I remember that there was an issue with CONFIG_NO_HZ. 

I have NO_HZ

> In my current hardpps kernel CONFIG_NO_HZ is set (y). 
> Considering the 'rock solid' offset of 127 us, should I change this to 'n' ?

Any guru's?

Udo