API docs: https://crabel99.github.io/SerialRTT/

SerialRTT is an Arduino Stream implementation backed by SEGGER RTT.

It is intended as a fast debug-output alternative to USB CDC serial for Cortex-M/A/R, RISC-V, and ARMv8-AR projects where a J-Link debugger is available.

Features

Stream/Print compatible API (print, println, printf, read, available)
No USB stack dependency for debug logging
Works with SEGGER RTT Viewer and J-Link GDB workflows
Optional non-blocking write mode via SEGGER_RTT_MODE_NO_BLOCK_SKIP

Installation

Add as a library dependency in PlatformIO or copy into your lib/ folder.

Quick Start

#include <Arduino.h>
#include <SerialRTT.h>
 
void setup() {
  SerialRTT.begin();
  SerialRTT.println("SerialRTT online");
}
 
void loop() {
  static uint32_t counter = 0;
  SerialRTT.print("count=");
  SerialRTT.println(counter++);
  delay(500);
}

See examples/basic_serial_rtt/basic_serial_rtt.ino for a complete example.

Compatibility

Framework: Arduino
Primary target: ARM Cortex-M boards where SEGGER RTT is usable
Typical workflow: firmware + J-Link + RTT Viewer

PlatformIO Integration

Example platformio.ini snippet using J-Link RTT and the bundled pre-test helper script:

[env:test_samd]
platform = atmelsam
framework = arduino
board = adafruit_feather_m0
upload_protocol = jlink
debug_tool = jlink
test_port = socket://localhost:19021
extra_scripts = pre:$PROJECT_LIBDEPS_DIR/$PIOENV/SerialRTT/scripts/pre_test.py
lib_deps =
  https://github.com/crabel99/SerialRTT.git
 
build_flags =
  -DBUFFER_SIZE_UP=8192
  -DSERIALRTT_USE_SKIP_NO_LOCK

Notes:

scripts/pre_test.py starts JLinkGDBServerCLExe and opens the RTT socket.
When used as a lib dependency, reference it via $PROJECT_LIBDEPS_DIR/$PIOENV/SerialRTT/scripts/pre_test.py.
Set JLINK_DEVICE to a SEGGER-supported device name if auto-detection is not sufficient.

Standard PlatformIO options used by the pre-test script:

test_port = socket://localhost:19021
upload_protocol = jlink       ; SWD
; upload_protocol = jlink-jtag ; JTAG

SEGGER RTT Subtree

This repo vendors SEGGER RTT under src/SEGGER_RTT via git subtree.

One-time setup:

git subtree add --prefix src/SEGGER_RTT https://github.com/SEGGERMicro/RTT.git main --squash

Updates are handled by the scheduled workflow in .github/workflows/segger-subtree.yml.

Licensing

This repository includes code under multiple licenses:

Project wrapper/integration code: MIT (see LICENSE)
Bundled SEGGER RTT source files: SEGGER RTT license terms in file headers

See THIRD_PARTY_NOTICES.md for details.