RTT Console over J-Link

tip

The RTT console gives you the Zephyr shell plus a live firmware log stream, so it is the recommended console for development and debugging. For day-to-day configuration, use the AT Console over USB-C instead. It requires no special hardware.

This page shows you how to attach to GLIDER through a Segger J-Link debug probe using the RTT (Real-Time Transfer) protocol. RTT gives you the full Zephyr shell plus live firmware logs, so it is the recommended console for development and debugging.

When to use this console

	RTT (rttt)	AT over USB-C (west serial-console)
Path	J-Link → SWD → RTT	USB-C → FT234XD → UART0
What you see	Zephyr shell + logs	AT commands + @LOG: messages
Hardware required	J-Link probe + SWD wires	Just a USB-C cable
Best for	Development, debugging, flashing, reset	Day-to-day provisioning

info

If you do not need full developer access, use the AT console over USB-C instead. It requires no special hardware.

Prerequisites

You need three things on your computer:

1. System packages (Python, venv, Git):

sudo apt update
sudo apt install python3 python3-venv git

2. Segger J-Link software pack installed. Verify with:

which JLinkExe
# /usr/bin/JLinkExe

If JLinkExe is missing, download the J-Link software from Segger's website and install it.

3. The rttt CLI available in your active Python virtual environment:

source .venv/bin/activate
which rttt
rttt --version

If rttt is missing inside the venv, install it:

pip install rttt

Hardware

• J-Link probe (external Segger probe or the on-board J-Link of a Nordic devkit).
• USB cable from the J-Link to your computer.
• SWD wires wired to the GLIDER debug header: SWDIO, SWCLK, GND, VTref.
• A powered GLIDER (from its own power supply or via VTref from the probe).

Launching the console

With the venv active:

rttt --device nRF9151_xxCA

caution

The device identifier must be nRF9151_xxCA, with lowercase xx and uppercase CA. The default identifier xxAA collides with J-Link DLL versions ≥ V9.42 and the connection will silently fail.

If you have more than one J-Link plugged in, select one by its serial number:

rttt --device nRF9151_xxCA --serial 123456789

To reset the device on attach (useful if the firmware crashed):

rttt --device nRF9151_xxCA --reset

What you get

An interactive Zephyr shell with prompt uart:~$:

• Live logs stream past as they happen.
• Shell commands can be typed and executed directly.

A few useful commands to get started:

help # list all commands
device list # list Zephyr devices
kernel uptime # time since last boot
kernel reboot cold # cold restart
log disable # silence logs for a clean shell
log enable wrn # show only warnings and above
info show # device info: serial number, claim token, version

GLIDER-specific commands include app, inputs, therm, alarm, modbus, and led. See the Shell Commands reference for the full list.

Exiting

Press Ctrl+C or simply close the terminal window.

Troubleshooting

Failed to open J-Link

Another process is holding the probe (nrfjprog, another rttt session, Segger Ozone, a VS Code debugger, etc.). Find and close it:

ps aux | grep -i jlink

Could not find requested device

• Check the device identifier: it must be nRF9151_xxCA (lowercase xx, uppercase CA).
• Confirm the GLIDER is powered.
• Verify SWD wires (SWDIO, SWCLK, GND, VTref) are connected correctly.
• Run JLinkExe interactively and connect to confirm the probe can see the target.

Console attaches but the prompt uart:~$ never appears

The firmware is not running or has crashed. Reset the device on attach:

rttt --device nRF9151_xxCA --reset

pylink-square complains about libjlinkarm.so.X

The J-Link software pack version installed does not match the library version pylink-square expects. Reinstall the latest J-Link pack, or point LD_LIBRARY_PATH to it:

export LD_LIBRARY_PATH=/opt/SEGGER/JLink:$LD_LIBRARY_PATH