rtt-tools

name	rtt-tools
description	Use when debugging embedded firmware through SEGGER J-Link RTT - capture RTT output, send RTT console commands, or open an interactive RTT console.

RTT Tools

Use scripts/rtt.py for SEGGER J-Link RTT.

RTT is RTOS-independent. Do not assume Zephyr unless the project clearly uses Zephyr/NCS.

Requirements

Firmware must:

• include SEGGER RTT support
• expose an RTT control block
• configure an up-buffer for target output
• configure and consume a down-buffer if input is needed
• route its shell/console/log backend to RTT if shell/log access is expected

Setup

RTT=/path/to/skills/rtt-tools/scripts/rtt.py

Defaults:

Interface: SWD
Speed: 4000
GDB port: 2331
RTT port: 19021

Use --dev-id <serial> when multiple J-Links are connected.

Commands

Run one command:

python "$RTT" command -d <device> "help"

The tool suppresses J-Link startup noise by default. Use --verbose only when diagnosing the J-Link server itself.

Open console:

python "$RTT" console -d <device>

Capture reset logs:

python "$RTT" capture -d <device> --reset --seconds 10

Attach to an existing RTT server:

python "$RTT" command --attach "help"

Useful options:

--timeout <seconds>    command timeout
--seconds <seconds>    capture duration
--gdb <path>           explicit GDB path
--no-drain             keep old RTT buffered data
--no-strip-ansi        keep ANSI escapes in command output
--verbose              show JLinkGDBServer startup output

Procedure

1. Build and flash with the project’s normal workflow.
2. Use capture --reset for boot logs.
3. Use command for automated shell checks.
4. Use console only for human interaction.
5. Stop this tool before starting another tool that needs the same J-Link or ports.

Zephyr / NCS Notes

Only apply this section to Zephyr/NCS projects.

Shell over RTT usually needs:

CONFIG_USE_SEGGER_RTT=y
CONFIG_SHELL=y
CONFIG_SHELL_BACKEND_RTT=y

Logging over RTT usually needs:

CONFIG_LOG=y
CONFIG_LOG_BACKEND_RTT=y

If shell and logging share channel 0, check for RTT channel/buffer conflicts.

Example for nRF54L15:

python "$RTT" capture -d NRF54L15_M33 --reset --seconds 10
python "$RTT" command -d NRF54L15_M33 "help"
python "$RTT" console -d NRF54L15_M33

Troubleshooting

No output:

• check J-Link visibility
• check device name
• check flashed image is running
• check firmware initializes RTT
• check RTT up-buffer exists

Command has no response:

• first confirm output works
• check RTT down-buffer exists
• check shell reads from RTT
• try a simple known command: help, version, or status

Missing early logs:

python "$RTT" capture -d <device> --reset --seconds 10

Old logs before new boot logs:

• keep default drain behavior
• avoid --no-drain

Port conflict:

• stop other J-Link/RTT tools
• or use --attach

GDB not found:

python "$RTT" capture -d <device> --reset --gdb /path/to/gdb --seconds 10

Reporting

Report:

• command used
• reset or attach mode
• relevant output
• whether RTT output worked
• whether RTT input worked