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Testing Digital Solutions

Raspberry Pi Zero Time Servers Documentation

Now that TGU is selling Pi Zero NTP time servers as part of its packages online we thought we'd go ahead and test them. There's already allot of excellent documentation on the intertubes on how to setup a NTP server using Pi's so we wont go into to much detail here. We will however, provide some of basic info and some of the test results we've obtained.

Reference

See the Stratum-1-Microserver HOWTO by the ntpsec people to see how things are done properly.

Bill of Materials

System Details

        os-release: gcc version 12.2.0 (Raspbian 12.2.0-14+rpi1) 
        uname:      Linux .... 6.6.20+rpt-rpi-v6 #1 Raspbian
        ntpd:       ntpsec-1.2.2
        hostapd:    v2.10
        dnsmasq:    2.89
        shorewall:  5.2.8-2

Pin Out

        ---------------------          -------------
        | Pi Zero           |          | GPS Board |
        |-------------------|          |-----------|
        | Pin 2  5V Power   |          |           |
        | Pin 4  5V Power   |<-------->| VCC       |
        | Pin 6  Ground     |<-------->| GND       |
        | Pin 8  GPIO 14 TX |<-------->| RX        |
        | Pin 10 GPIO 15 RX |<-------->| TX        |
        | Pin 12 GPIO 18    |<-------->| PPS       |
        ---------------------          -------------

Configs

boot/firmware/config.txt

...
[all]
enable_uart=1
dtoverlay=pi3-disable-bt-overlay
dtoverlay=pi3-miniuart-bt
dtoverlay=disable-bt
dtoverlay=pps-gpio,gpiopin=18

boot/firmware/cmdline.txt

console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 fsck.repair=yes rootwaiti bcm2708.pps_gpio_pin=18

/etc/default/ntpsec

NTPD_OPTS="-g"
IGNORE_DHCP="yes"
NTPSEC_CERTBOT_CERT_NAME=""

/etc/ntpsec/ntp.conf

driftfile /var/lib/ntpsec/ntp.drift
leapfile /usr/share/zoneinfo/leap-seconds.list
refclock shm unit 1 prefer refid PPS
refclock shm unit 0 refid GPS
restrict -4 default kod nomodify limited
restrict 192.168.0.0/8
restrict 10.10.0.0/8
restrict 127.0.0.1
restrict ::1

Testing

For testing we will be using four GPS PPS stratum1 time servers. Two of which will be Pi zero's and the other two are Pi three's that serve network time in the office. For the sake of this test we will call these hosts PiZero1, PiZero2, PiThree1 and PiThree2. Below is some sudo python code demonstrating how the test data was obtained using to "ntprace" command. 

loops = 20
results = {}
for i in loops:
    for host in hosts:
        result = subprocess.checkout_output(["ntptrace", ip)
        results[host][distance] = result[distance]
        results[host][offset] = result[offset]

for host, data in results:
    print us -> host, offset: sum(data[offset])/loops, distance: sum(data[distance])/loops

The Test Results

From To Offset ( Secs ) Synch Distance ( Secs )
PiZero1 PiThree1 0.0000139 0.0011013
PiZero1 PiThree2 0.0000275 0.0011042
PiZero1 PiZero2 0.0000153 0.0011230
PiZero2 PiThree1 0.0000129 0.0011252
PiZero2 PiThree2 0.0000267 0.0010975
PiZero2 PiZero1 0.0000185 0.0010930
PiThree1 PiThree2 0.0000260 0.0011110
PiThree1 PiZero1 0.0000000 0.0011042
PiThree1 PiZero2 -0.0000055 0.0010998
PiThree2 PiThree1 0.0000150 0.0011230
PiThree2 PiZero1 0.0000010 0.0011185
PiThree2 PiZero2 -0.0000050 0.0010862

Conclusions

Not bad for a couple of Pi Zero's : )


In Memory

To those who gave us time.

Pi Zero Stratum 1

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