Discussion: Interesting fixed latency on Pi Zero W

[BlipRanger]

Hi, I know you recommend a Pi 4/5 but I tried this out on a Pi Zero W and did manage to get stratum 1 with it, which is cool. However, I noticed something interesting which is that when checking the sources, PPS will always have exactly +/-1000ns of latency. Is this a hardware limitation you think? Just a curiosity and not a real issue. Feel free to close whenever.

210 Number of sources = 10
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
#x NMEA                          0   4   377    11    -70ms[  -70ms] +/-  397us
#* PPS                           0   4   377     9    -32ns[  -36ns] +/- 1000ns
^- 192.168.1.1                   3   5   377    16    -25ms[  -25ms] +/-   40ms
^- 65.73.197.211                 3   6   277    48  -9501us[-9501us] +/-   80ms
^- 152.70.159.102                2   6   337    48    -11ms[  -11ms] +/-  112ms
^- 104.167.241.197               2   6   377    49  +5777us[+5777us] +/-   26ms
^- 135.148.100.14                2   6   377    49  -4120us[-4120us] +/-   41ms
^- 168.61.215.74                 3   6   377    54    -24ms[  -24ms] +/-   92ms
^- 17.253.20.125                 1   6   337    56    +57ms[  +57ms] +/-   74ms
^- 132.163.96.1                  1   6   277    50  +9676us[+9677us] +/-   38ms

chronyc> tracking
Reference ID    : 50505300 (PPS)
Stratum         : 1
Ref time (UTC)  : Sat Jan 13 02:44:03 2024
System time     : 0.000000122 seconds slow of NTP time
Last offset     : -0.000000128 seconds
RMS offset      : 0.001089404 seconds
Frequency       : 6.724 ppm fast
Residual freq   : +0.000 ppm
Skew            : 0.023 ppm
Root delay      : 0.000000001 seconds
Root dispersion : 0.000013824 seconds
Update interval : 16.0 seconds
Leap status     : Normal