RTT ARM Cortex SWD/JTAG Logging GUI

Table of Contents

• Overview
• Features
• Prerequisites
  • Host Software
  • Embedded Target Setup
• Installation
  • Download Executable
  • Manual Installation
• Usage
  • Demo Mode
  • Connecting to an MCU
  • Log Tab
  • Data Series Tab
  • Plot Tab
• Configuration
• License

Overview

This project provides a Python-based GUI to display, filter and highlight real-time ARM Cortex microcontroller log messages received via SEGGER's Real-Time Transfer (RTT) debug protocol.

This debug protocol provides direct communication with ARM Cortex-based microcontrollers via J-Link debug probes. RTT removes the need for additional debug channels during development (like UART) by using the ARM Cortex SWD/JTAG interface. Unlike the slower and clunkier UART debug channel the SWD, JTAG interface provides lean and mean RTT debug messages for ARM MCUs.

This project interfaces directly with the J-Link debug probe drivers, using the Python library pylink which wraps the JLink drivers to interact with a J-Link debug probe. It does NOT require any other intermediary software like Segger's RTT Viewer.

The pylink library was written by Square Inc. (Now Block Inc.), open sourced https://github.com/square/pylink and uploaded to PyPI https://pypi.org/project/PyLink/.

The official documentation and examples for the pylink library are somewhat lacking when it comes to using the RTT channel, so this project may also serve as a practical guide for leveraging pylink for RTT communication.

Features

• Direct J-Link connection using native drivers (no other software required)
• Real-time log display with filtering and message highlighting
• Data Series — define named patterns with <N> capture groups to extract numeric values from log lines
• Pattern Generator — auto-generate patterns from sample log lines
• Real-time plotting — plot up to 3 data series simultaneously with modern dark charts
• Activate/Deactivate series independently
• Pause/Resume log display
• Save logs to file
• MCU history — remembers recently used MCUs
• Config persistence — MCU history, interface selection, and data series are saved automatically
• Demo mode — test without hardware using --demo-messages

Prerequisites

Host Software

• Python 3.8+ (https://www.python.org/)
• SEGGER J-Link Software (Download)
• Required Python packages (see requirements.txt):
  • FreeSimpleGUI
  • pylink-square
  • platformdirs
  • matplotlib

Embedded Target Setup

Include the SEGGER RTT library in your embedded application. See: https://www.segger.com/products/debug-probes/j-link/technology/about-real-time-transfer/

#include "SEGGER_RTT.h"

void main() {
    SEGGER_RTT_Init();
    SEGGER_RTT_SetTerminal(0);
    SEGGER_RTT_printf(0, "System started\n");
}

Installation

Download Executable

Download the matching executable (Windows or Linux) from the releases page: https://github.com/SaturnIC/RTT-ARM-Cortex-GUI/releases

Manual Installation

1. Clone the repository:

   git clone https://github.com/SaturnIC/RTT-ARM-Cortex-GUI.git
   cd RTT-ARM-Cortex-GUI

2. Install dependencies:

   pip install -r requirements.txt

3. Ensure J-Link drivers are installed on your system.
4. Launch:

   python rtt_python_gui.py

Usage

Demo Mode

Test the application without hardware using the built-in demo mode:

python rtt_python_gui.py --demo-messages

This replays a sample log file so you can explore filtering, highlighting, data series, and plotting.

Connecting to a real MCU

1. Connect MCU via J-Link to your PC
2. Select your target MCU from the dropdown. Type to filter the list.
3. Select the interface (SWD or JTAG).
4. Click Connect. The status dot turns green when connected.
5. Click Disconnect to terminate the connection.

Log Tab

• Filter — type a substring to show only matching log lines
• Highlight — type a substring to highlight matching text in the log
• Pause — freeze the log display while data continues to be received
• Clear — reset the log display
• Save — export the log to a text file

Data Series Tab

Define named data series that extract numeric values from log lines using patterns.

Defining a series:

1. Enter a Name for the series.
2. Define a Pattern — use <N> to capture a number and * to match any text.
3. Click Add to create the series.

Pattern examples:

Log line	Pattern	Captured value
ADC value: 3.14 V	ADC value: <N> V	3.14
Sensor1=100 Sensor2=200	Sensor1=<N> *	100
Temperature: 25.6	*: <N>	25.6

Pattern Generator: Click Pattern Generator to open a dialog where you can paste a sample log line, type the number to capture, and the pattern is generated automatically.

Activate/Deactivate: Select a series in "Defined Series" and click Activate to start capturing data. Use Deactivate to stop. Only active series are plotted.

Clear Data: Click Clear Data next to "Recorded Values" to clear all captured values.

Plot Tab

Select up to 3 data series from the dropdowns to plot them in real-time. All series share the same time origin. The chart features:

• Smooth line interpolation
• Glow effect and gradient fill under lines
• Auto-scaling Y-axis
• Custom toolbar (Home, Back, Forward, Pan, Zoom, Save)

Configuration

The application stores configuration (MCU history, interface selection, data series definitions) in a JSON file at the platform-appropriate user data directory. This is saved automatically on exit or when settings change.

Development

For development setup, testing, and building executables, see docs/DEVELOPMENT.md.

License

This project is licensed under the Apache License, Version 2.0. See LICENSE for more details.