jlink-rtt

name

jlink-rtt

description

Read SEGGER RTT log output in real-time via J-Link debugger, supporting auto-scan of RTT control block addresses, applicable for debugging GD32/STM32 and other ARM Cortex-M microcontrollers. Trigger scenarios: (1) Read RTT debug logs from microcontroller, (2) User mentions "RTT", "view logs", "read serial" (RTT scenario), "real-time logs", (3) Need to view output information when debugging microcontroller programs, (4) Using features similar to SEGGER RTT Viewer. Even if user just says "see what the microcontroller prints" or "read RTT", this skill should be used.

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.