LNode Firmware: USB Serial Ports

A flashed LNode presents two USB CDC-ACM serial ports to the host. Knowing which is which is the difference between reading a debug log and talking the Reticulum transport protocol.

The two ports

The firmware exposes two CDC-ACM serial ports. The lower-numbered port is the debug log output; the higher-numbered port is the Reticulum transport interface that carries HDLC frames. The actual /dev/ttyACM* numbers depend on what else is plugged into USB.

The firmware exposes two USB CDC-ACM serial ports. The lower-numbered port is the debug log output. The higher-numbered port is the Reticulum transport interface that carries HDLC frames. The actual /dev/ttyACM* numbers depend on other connected USB devices. (reticulum-nrf/README.md:44-46)

Each CDC-ACM class occupies two USB interfaces (a Communication interface plus a Data interface), so the two ports map onto four USB interface numbers:

(reticulum-nrf/udev/99-leviculum.rules, header comment.)

Stable device paths via udev

Because the /dev/ttyACM* enumeration order is not stable, install the shipped udev rules to get fixed symlinks:

sudo cp udev/99-leviculum.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules

(reticulum-nrf/README.md:50-53)

After the next plug-in, the symlinks point at the correct ports regardless of enumeration order. The names are board-family specific, keyed off the per-board USB PID:

(Symlink names and PIDs: reticulum-nrf/udev/99-leviculum.rules. The firmware-side USB VID/PID constants: reticulum-nrf/src/boards/t114.rs:139-140 for 1209:0001, reticulum-nrf/src/boards/rak4631.rs:126-127 for 1209:0002.)

Multiple boards of the same kind. The short symlinks (/dev/leviculum-transport) land on whichever device udev sees first. The rules also emit per-serial-number symlinks (/dev/leviculum-transport-<SERIAL>); use those when more than one board of the same family is attached. (reticulum-nrf/udev/99-leviculum.rules, header comment and SYMLINK+="leviculum-transport-%s{serial}" lines.)

Reading the debug port

The debug port is plain text at 115200 baud:

picocom /dev/leviculum-debug -b 115200

(reticulum-nrf/README.md:59-60)

On the debug port you will see the boot banner, the firmware git SHA, the node identity, and the periodic diagnostics the firmware emits — for example the LNode started -- identity: … line and the [FW_BUILD] banner re-emitted every few seconds. (reticulum-nrf/src/bin/t114.rs:164-168, :323-333.) Do not point lnsd at the debug port; it carries log text, not HDLC frames.

Pointing lnsd at the transport port

The transport port speaks the RNode LoRa framing protocol over HDLC, the same wire protocol lnsd/rnsd use for an RNode. Configure it as an RNodeInterface (the dedicated single-radio RNode driver) with its port set to the transport symlink.

The radio parameters in the config must match the firmware’s compiled-in defaults (the EU medium profile), otherwise the two sides talk past each other on the air. (reticulum-nrf/README.md:8; reticulum-nrf/src/lora.rs:124-138.)

[interfaces]

  [[LNode T114]]
    type = RNodeInterface
    enabled = yes
    port = /dev/leviculum-transport
    frequency = 869525000
    bandwidth = 125000
    txpower = 17
    spreadingfactor = 7
    codingrate = 5

The key names and types come from the [[RNode Interface]] config schema (port, frequency, bandwidth, txpower, spreadingfactor, codingrate; docs/src/rnode-protocol.md:674-684). The values above are the firmware’s compiled defaults: 869.525 MHz, BW 125 kHz, 17 dBm, SF7, CR4/5 (reticulum-nrf/src/lora.rs:124-138).

For a RAK4631 / WisMesh Pocket V2 the only change is the port:

  [[LNode Pocket V2]]
    type = RNodeInterface
    enabled = yes
    port = /dev/leviculum-rak-transport
    frequency = 869525000
    bandwidth = 125000
    txpower = 17
    spreadingfactor = 7
    codingrate = 5

After editing /etc/reticulum/config, restart the daemon so it picks up the new interface:

sudo systemctl restart lnsd

(Same restart flow as any config change; see the lnsd Quickstart.)

Confirming the link came up

Run the standard health-check and look for the new interface in the interface_stats section with status=up and non-zero counters once LoRa traffic flows:

lns diag --config /etc/reticulum

(lns diag usage and the interface_stats reading are described in the lnsd Quickstart.)

For the full key-by-key reference of the [[RNode Interface]] section and the meaning of the optional keys (flow_control, airtime_limit_*, callsign beaconing), see the Configuration chapter and docs/src/rnode-protocol.md.