Skip to content

NTPServer.md

Latest commit

 

History

History
101 lines (65 loc) · 5.31 KB

NTPServer.md

File metadata and controls

101 lines (65 loc) · 5.31 KB

Raspberry Pi NTP Server

I've been running a couple GPS-based Raspberry Pi NTP servers for a while. Here are the steps I follow to set up a new one.

Credit

The following pages helped with this process

I'm using Jessie Lite (2015-11-21-raspbian-jessie-lite.img) as I document this.

Hardware Requirements

I'm using the following hardware:

Life would have been a lot easier if I'd just waited and instead acquired:

In order to simplify construction I soldered four pins of the GPS board to the perma-proto board. In order to get the PPS to pin 18 on the Raspberry Pi I snuck a wire in underneath that you can sort-of see in the edge-on picture (sorry about the mess on that GPS board, I'd soldered the full header in during prior experimentation and had to remove it).

Overview of board Edge-on view

Initial Setup

I follow my own guide for the initial setup but note the following change and detail:

  • On raspi-config step 9, I use the "Serial" option to disable the serial console.
  • If you use dhcp, ensure you perform the last step on that page to stop the dhcp server from overwriting your ntp configuration file.

Configuration as NTP server

According to David Taylor's user-mode configuration instructions, we've already achieved the top 5 bullet points! Next we'll set up GPSD.

gpsd setup

  1. Install gpsd: sudo apt-get install gpsd gpsd-clients

  2. Edit /etc/default/gpsd as root to set things up:

    • Change the DEVICES line to read: DEVICES="/dev/ttyAMA0"
    • Change the GPSD_OPTIONS line to read GPSD_OPTIONS="-n"

  3. Restart gpsd sudo service gpsd restart

  4. Verify gps stuff is working: cgps -s - we're mostly looking for Status: 3D FIX.

  5. q to exit cgps.

  6. Due to what seems to be a systemd configuration problem, we have to tell Raspbian to start gpsd on boot. Edit /lib/systemd/system/gpsd.service and find the [Install] section and insert a line between that section header and the Also=gpsd.socket line:

     [Install]
 WantedBy=multi-user.target
 Also=gpsd.socket

    Then run sudo systemctl enable gpsd.service.

  7. If you want, do a sudo reboot to restart and then log in and run ps auxw |grep gpsd to ensure gpsd is starting on boot and cgps -s again to make sure everything continues to work.

Get ntpd talking to the gps

  1. Edit /etc/ntpd.conf and add this section so we can figure out an appropriate fudge value to use for your configuration:

     # Server to be monitored only, not selected for syncing
 server 127.127.28.0 minpoll 4 maxpoll 4 noselect
 fudge 127.127.28.0 time1 0.000 refid GPSD

    You can add a couple other servers if you'd like (or leave some pool servers enabled), as well. Restart ntpd with sudo service ntp restart.

  2. Wait a bit. You should see when you run ntpq -p that it's getting good updates (there'll be an offset and your reach column will ultimately read 377).

  3. Once you see a reach value of 377, start running ntpq -p every minute or two and check out the offset column. You'll want to come up with an average of these numbers.

  4. Edit your /etc/ntpd.conf and update the value after time1 to be the average number you got from the offset column multiplied by -0.001 (e.g. if your average value was -477 you'll enter 0.477 as your fudge value. You can also remove the noselect so that ntpd will start using this time source when we restart it next.

Get PPS coming from the gps

  1. Download the latest rpi_gpio_ntp software from www.vanheusden.com - currently that's version 1.5 (curl -O https://www.vanheusden.com/time/rpi_gpio_ntp/rpi_gpio_ntp-1.5.tgz).

  2. Decompress it (tar -zxvf rpi_gpio_ntp-1.5.tgz). Change into the directory (cd rpi_gpio_ntp-1.5).

  3. Build the software and install it to /usr/local/bin/ with sudo make install.

  4. Verify PPS operation with sudo /usr/local/bin/rpi_gpio_ntp -g 18 -d - this command assumes GPIO pin 18 (see the Hardware Requirements above).

  5. You should see some interrupts coming in. If so, hit Control-C to get out of this software.

  6. Edit /etc/rc.local and add the following line before exit 0 at the bottom of the file:

     /usr/local/bin/rpi_gpio_ntp -N 1 -g 18

  7. Edit your /etc/ntp.conf again to add the PPS source:

     server 127.127.28.1 minpoll 4 prefer
 fudge 127.127.28.1 refid UPPS

  8. sudo reboot to make sure everything comes up properly on boot.

  9. Use ntpq -p to see if you are getting time updates and how they compare to other servers.