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Summary (version 0.1-3)

This package installs an automatic PPP network link on an RPi900 via its DNT900 radio.

When the RPi900 is serving as a network-connected base station, the package provides an automatic network connection to any remote RPi900s which connect to the base radio. This includes the necessary setup of routing and DNS so that the remote radio may be fully networked using only the DNT900 radio link.

When the RPi900 is serving as a remote radio, the package provides an automatic network connection via the base radio to which the remote radio is connected. For a remote RPi900, the connection can be made with or without the DNT900 line discipline installed.


Prior to building and installing this package, you should first install the rpirtscts dependency. You can also install the rpi900 package, which is required for an RPi900 base station and optional for a remote station.


You must be root to make changes to the /etc/rpi900-ppp.conf configuration file. First, choose a static IP address for the RPi900 on your local network. (This may also require you to put aside some static IP address space in your router.) For the base radio, the IP address should be that already in use. Edit the configuration file, setting the IPADDRESS variable to the chosen IP address:

nano /etc/rpi900-ppp.conf

If the RPi900 is operating as a base station, you'll also need to set PROXY to the name of the network interface being used to connect to the local network. (This will be eth0 for ethernet, or wlan0 for a wifi adapter.) This is required for the base station to act as a proxy for address resolution.

If the RPi900 is operating as a remote station, and you don't intend to use the DNT900 line discipline (the rpi900 package), you should also set SPEED to the serial rate you're using with the radio.

Next, configure PPP authentication, which is enabled in Linux by default. It may be preferable to control access using one of the DNT900's authentication methods. In this case, disable PPP authentication by adding OPTIONS=noauth to /etc/rpi900-ppp.conf.

Alternatively, add lines to /etc/ppp/chap-secrets to configure passwords for various connections. For example, to add a universal password of sesame for all PPP clients:

echo "* * sesame" >> /etc/ppp/chap-secrets

With replaced by your local subnet in CIDR notation.

By default the RPi900 base station will start a PPP link for every radio which connects. If you wish to restrict PPP services to certain radio MAC addresses, whitelist them as follows:

touch /etc/rpi900-ppp.d/0x00165E.allow  # only start PPP for radio with MAC 0x00165E ...
touch /etc/rpi900-ppp.d/0x000E3F.allow  # ... or with MAC address 0x000E3F

Alternatively, you can blacklist specific MAC addresses and run PPP on all others:

touch /etc/rpi900-ppp.d/0x0022A6.deny   # don't start PPP for radio with MAC 0x0022A6

(Don't mix .allow and .deny configurations; it won't work!)


Once the package is installed, reboot the RPi900(s). Udev rules provided by the package will automatically start a PPP connection as the radio TTYs appear. If configured correctly, you should be able to ping the remote RPi900 via its IP address. Then login to the remote via ssh and ping google.com to check full network connectivity including DNS. Finally, try rebooting the remote and base RPi900s to confirm that the network connections come back up automatically.

You can observe the status of the PPP connection:

systemctl status rpi900-ppp*

Or observe the log:

sudo journalctl -b -u rpi900-ppp*

Operation in Transparent Mode

On a remote RPi900, it is possible to use this package without using the DNT900 line discipline provided by the rpi900) package. (In this case, the radio is operated in transparent mode.) This may be desirable to reduce computational load, and if the remote Raspberry Pi has no need to access its own radio's registers. If you choose this option, enable the rpi900-ppp service as follows:

sudo systemctl enable rpi900-ppp

(You will need to disable this service if you decide to install the rpi900 service, since they conflict.)

Certain DNT900 register values must be set correctly in order to use transparent mode. In particular, ProtocolMode should have a value of 0x00 and RmtTransDestAddr should be 0x000000 to allow transparent-mode communication to the base station. (These values are the factory defaults.) To prevent inadvertent activation of protocol mode, you'll probably also want to set ProtocolSequenceEn to a value of 0x01.

Package Contents

The package installs the following files:

  • /usr/lib/systemd/system/rpi900-ppp-base@.service: this systemd service is a PPP daemon for use by a remote radio connectedn to a base station. The connection is set up as the default route and obtains DNS from the base.
  • /usr/lib/systemd/system/rpi900-ppp-remote@.service: this systemd service is a PPP daemon for use by a base radio and provides a PPP service to a remote radio. Proxy address resolution is provided for the remote via the internet-facing network interface.
  • /usr/lib/systemd/system/rpi900-ppp.service: this systemd service is also a PPP daemon for use by a remote radio, however it attaches directly to ttyAMA0 and requires the radio to be in transparent mode.
  • /usr/lib/udev/rules.d/99-rpi900-ppp.rules: this udev rules file monitors the DNT900 service for the connection of new radios. The first rule triggers when ATTRS{DeviceMode}=="0x01", correspondinging to the connection of the base radio, and launches the base PPP service. The second rules triggers when ATTRS{local/DeviceMode}=="0x01"--in other words, when the RPi900 is acting as the base (and the connecting radio therefore a remote). In this case, the remote PPP service is launched.
  • /etc/rpi900-ppp.conf: edit this configuration file to set the static IP address for the RPi900, and other parameters.
  • /etc/rpi900-ppp.d/: for a base station, add 0xXXXXXX.allow or 0xXXXXXX.deny files to this directory to allow or deny PPP for specific radio MAC addresses.

Release History

  • 2014/04/22: version 0.1-1: initial release.
  • 2014/04/28: version 0.1-2: add rpi900 package as a dependency.
  • 2014/04/29: version 0.1-3: add rpi900-ppp.service for use without DNT900 line discipline.