Jlink Rtt

J-Link RTT Log Reading

Invoke py_jlink_rtt.py to connect to target chip via J-Link and read SEGGER RTT terminal output in real-time. Supports auto-scan to locate RTT control block in memory, and also supports manually specifying the address.

Tool Script

Script Path: py_jlink_rtt.py Dependencies: Python 3.x + pylink library

pip install pylink

Usage

# Default parameters (GD32F303RC, auto-scan RTT address, 60 second timeout)
python py_jlink_rtt.py

# Specify chip model
python py_jlink_rtt.py -d STM32F103C8

# Manually specify RTT control block address (skip auto-scan, faster startup)
python py_jlink_rtt.py -a 0x20000B90

# Read channel 1, 30 second timeout, enable debug output
python py_jlink_rtt.py -c 1 -t 30 --debug

# Monitor logs while sending data at regular intervals (supports multiple --send)
python py_jlink_rtt.py -d GD32F303RC -t 10 --send 3:hello --send 6:test

Parameter Description

| Parameter | Short | Description | Default | | ------------- | ----- | ---------------------------------- | ------------- | | --device | -d | Target chip model | GD32F303RC | | --channel | -c | RTT channel number | 0 | | --timeout | -t | Running time (seconds) | 60 | | --rtt-addr | -a | RTT control block address (hex) | Auto-scan | | --send | -s | Send data at regular intervals (format see below) | Not send | | --debug | - | Print rtt_read return type | Off |

--send Parameter Format

--send seconds:content

• seconds: Time point to trigger sending (relative to when connection starts)
• content: String data to send
• Can use multiple --send for multiple sends

Example:

# Send "hello" at 3 seconds, send "start_test" at 7 seconds
--send 3:hello --send 7:start_test

RTT Control Block Address

• Auto-scan: The script uses a two-layer strategy: prioritize using J-Link SDK built-in rtt_start(0) to automatically locate the control block (more reliable); if SDK scan fails, fall back to Python manually scanning RAM area (starting from 0x20000000, 128KB range), searching for "SEGGER RTT" identifier. Recommended for first-time use.
• Manual specification: If the address is known (can be obtained from J-Link RTT Viewer or map file), use -a parameter to specify for faster startup.

> Note: After each firmware recompilation, the RTT control block address may change. It is recommended to re-auto-scan or check the new map file.

Working Principle

1. Connect J-Link to target chip via SWD interface
2. Locate RTT control block: prioritize J-Link SDK built-in auto-scan, fall back to Python manual scan on failure
3. Start RTT session, periodically call rtt_read() to read buffer
4. According to --send schedule, call rtt_write() to send data at regular intervals
5. Real-time output UTF-8 decoded content to terminal
6. Disconnect on Ctrl+C or when timeout is reached

Performance Tuning

The script has built-in batch read optimization (max 4096 bytes per read, 10ms refresh interval), suitable for high-frequency log scenarios. If garbled text appears, check if firmware RTT log uses UTF-8 encoding.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: changde-tang
• Source: changde-tang/embedded-skills
• License: MIT

Install and usage instructions live in the source repository linked above.