RTT output is missing

[jakobjung10]

Describe the bug

When I use the Cortex-Debug extension, I don't get RTT output.

However, when I use the Probe-rs VSCode-extension, RTT output works.
This means that there is no problem in the code itself.

Expected behavior

I expect to see RTT messages in a terminal or some kind of output window.

Screenshots

Environment (please complete the following information):

[comment]: <> Whenever possible, please make sure you are using the latest versions of VSCode and our extension

• Cortex-Debug Version 1.12.1
• OS: Windows 10
• GDB Version: GNU gdb (Arm GNU Toolchain 15.2.Rel1 (Build arm-15.86)) 16.3.90.20250906-git
• Compiler Toolchain Version: rustc 1.91.1 (ed61e7d7e 2025-11-07)
• Target: "thumbv6m-none-eabi"
• Device: "STM32F072VBTx"

Please include launch.json

{
            "name": "Debug: Cortex-Debug",
            "type": "cortex-debug",
            "request": "launch",
            "rttConfig": {
                "enabled": true,
                "address": "auto",
                "decoders": [
                    {
                        "label": "RTT",
                        "port": 0,
                        "type": "console"
                    }
                ]
            },
            "breakAfterReset": false,
            "servertype": "stlink",
            "device": "STM32F072VBTx",
            "interface": "swd",
            "cwd": "${workspaceFolder}",
            "executable": "${workspaceFolder}/target/thumbv6m-none-eabi/debug/apus-rs-demo",
            "svdFile": "${workspaceFolder}/device/STM32F0x2.svd",
            "preLaunchTask": "rust: cargo build",
            "showDevDebugOutput": "raw",
        },

Attach text from Debug Console

`[2025-12-28T19:52:23.369Z] SERVER CONSOLE DEBUG: onBackendConnect: gdb-server session connected. You can switch to "DEBUG CONSOLE" to see GDB interactions.
"C:\ST\STM32CubeIDE_1.17.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.stlink-gdb-server.win32_2.2.0.202409170845\tools\bin\ST-LINK_gdbserver.exe" -p 50000 -cp "C:\ST\STM32CubeIDE_1.17.0\STM32CubeIDE\plugins\com.st.stm32cube.ide.mcu.externaltools.cubeprogrammer.win32_2.2.0.202409170845\tools\bin" --swd --halt

STMicroelectronics ST-LINK GDB server. Version 7.9.0
Copyright (c) 2024, STMicroelectronics. All rights reserved.

Starting server with the following options:
Persistent Mode : Disabled
Logging Level : 1
Listen Port Number : 50000
Status Refresh Delay : 15s
Verbose Mode : Disabled
SWD Debug : Enabled

Waiting for debugger connection...
Debugger connected
Waiting for debugger connection...
-------------------------------------------------------------------
STM32CubeProgrammer v2.18.0
-------------------------------------------------------------------

Log output file: C:\Users\Jakob\AppData\Local\Temp\STM32CubeProgrammer_a40332.log
ST-LINK SN : 35FF71064E42363247392143
ST-LINK FW : V2J45S7
Board : --
Voltage : 3.24V
SWD freq : 4000 KHz
Connect mode: Under Reset
Reset mode : Hardware reset
Device ID : 0x448
Revision ID : Rev Z
Device name : STM32F07x
Flash size : 128 KBytes
Device type : MCU
Device CPU : Cortex-M0
BL Version : 0xA1

Opening and parsing file: ST-LINK_GDB_server_a40332.srec

Memory Programming ...
File : ST-LINK_GDB_server_a40332.srec
Size : 103.51 KB
Address : 0x08000000

Erasing memory corresponding to segment 0:
Erasing internal memory sectors [0 51]
Download in Progress:

File download complete
Time elapsed during download operation: 00:00:04.959`

Additional context
Add any other context about the problem here.

[haneefdm]

probe-rs does not support RTT like other probes do. They use a formatter (defmt) that we do not support, as it is not standard practice. However, there is a plugin that can be used to decode probe-rs RTT. You are on your own using that plugin. But, why not use the VSCode extension made for probe-rs instead of cortex-debug

https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger#:~:text=probe%2Drs%20Debug%20Adapter%20for%20VS%20Code.&text=Launch%20VS%20Code%20Quick%20Open,following%20command%2C%20and%20press%20enter.

If you google it, it says you should not mix cortex-debug and probe-rs

probe-rs is a standalone, native Rust embedded debugging toolkit that provides its own integrated Visual Studio Code extension with built-in Real-Time Transfer (RTT) functionality, rather than functioning as a plugin for the separate  extension. [[1](https://probe.rs/docs/), [2](https://probe.rs/docs), [3](https://probe.rs/), [4](https://probe.rs/docs/tools/debugger/#:~:text=probe%2Drs%20and%20the%20VS%20Code%20extension%20supports%20using%20RTT%20in%20your%20target%20application.), [5](https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger#:~:text=A%20VS%20Code%20(%20Visual%20Studio%20Code,of%20ARM%20Cortex%2DM%2C%20ARM%20Cortex%2DA%2C%20and%20RISC%2DV.)]  
 VS Code Extension for RTT [[6](https://probe.rs/docs/tools/debugger/#:~:text=Configuring%20RTT%20to%20transfer%20data.%20probe%2Drs%20and,under%20the%20cargo%2Dembed%20section%20of%20this%20guide.)]  
The primary way to use  with RTT in VS Code is through the official Debugger for probe-rs extension. This extension is designed for seamless debugging of embedded Rust applications and includes fully integrated RTT log capabilities. 

• Integrated RTT: RTT logs are directed to a VS Code terminal within the integrated debugging experience. 
• No Separate Plugin Needed: You do not need an extra "plugin" for RTT; it is a core feature of the  toolkit and its dedicated extension. 
• Ease of Use: It aims to simplify the configuration process compared to other solutions, with configuration often handled via an  file or launch configurations. [[1](https://probe.rs/docs/), [3](https://probe.rs/), [8](https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger#:~:text=probe%2Drs%20Debug%20Adapter%20for%20VS%20Code.&text=Launch%20VS%20Code%20Quick%20Open%20(%20Ctrl+P,paste%20the%20following%20command%2C%20and%20press%20enter.), [11](https://google.github.io/comprehensive-rust/bare-metal/microcontrollers/probe-rs.html), [12](https://www.eevblog.com/forum/microcontrollers/rust-tools-and-resources-for-embedded/#:~:text=probe%2Drs%2Ddebugger:%20a%20vscode%20extension%20that%20allows%20seamless,and%20how%20the%20can%20be%20automatically%20saved).)]  

You can install the official extension directly from the marketplace: 

• Debugger for probe-rs on Visual Studio Marketplace 
 
cortex-debug and probe-rs Interaction:

The  cortex-debug extension is a separate, well-established extension primarily designed to work with GDB servers like OpenOCD or J-Link GDB server, and it has its own support for RTT/SWO when configured correctly. [[15](https://marketplace.visualstudio.com/items?itemName=marus25.cortex-debug), [16](https://github.com/Marus/cortex-debug)]  
It is generally not recommended to try and use probe-rs as the GDB server for the  extension if you require RTT simultaneously. Historically, there have been limitations or difficulties in running the  GDB server and RTT channels at the same time within that specific configuration. The  team developed their own native VS Code extension to overcome such limitations and provide a more integrated experience. [[17](https://github.com/probe-rs/cargo-embed/issues/169), [18](https://embedded-trainings.ferrous-systems.com/gdb)]  
In summary, for the best experience with  and RTT, use the dedicated Debugger for probe-rs VS Code extension. 

AI responses may include mistakes.

[1] https://probe.rs/docs/
[2] https://probe.rs/docs
[3] https://probe.rs/
[4] [https://probe.rs/docs/tools/debugger/](https://probe.rs/docs/tools/debugger/#:~:text=probe%2Drs%20and%20the%20VS%20Code%20extension%20supports%20using%20RTT%20in%20your%20target%20application.)
[5] [https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger](https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger#:~:text=A%20VS%20Code%20(%20Visual%20Studio%20Code,of%20ARM%20Cortex%2DM%2C%20ARM%20Cortex%2DA%2C%20and%20RISC%2DV.)
[6] [https://probe.rs/docs/tools/debugger/](https://probe.rs/docs/tools/debugger/#:~:text=Configuring%20RTT%20to%20transfer%20data.%20probe%2Drs%20and,under%20the%20cargo%2Dembed%20section%20of%20this%20guide.)
[7] [https://open-vsx.org/extension/probe-rs/probe-rs-debugger](https://open-vsx.org/extension/probe-rs/probe-rs-debugger#:~:text=The%20official%20VS%20Code%20extension%20for%20probe%2Drs,of%20ARM%20Cortex%2DM%2C%20ARM%20Cortex%2DA%2C%20and%20RISC%2DV.)
[8] [https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger](https://marketplace.visualstudio.com/items?itemName=probe-rs.probe-rs-debugger#:~:text=probe%2Drs%20Debug%20Adapter%20for%20VS%20Code.&text=Launch%20VS%20Code%20Quick%20Open%20(%20Ctrl+P,paste%20the%20following%20command%2C%20and%20press%20enter.)
[9] [https://probe.rs/docs/tools/debugger/](https://probe.rs/docs/tools/debugger/#:~:text=Debugger%20The%20probe%2Drs%20VS%20Code%20extension%20uses,currently%20in%20pre%2Dproduction/Alpha%20stage%2C%20with%20limited%20functionality.)
[10] [https://www.circuitdojo.com/posts/debugging-the-nrf9151-feather-w-probe-rs](https://www.circuitdojo.com/posts/debugging-the-nrf9151-feather-w-probe-rs#:~:text=1.%20Install%20the%20probe%2Drs%20Debugger%20Extension%20Start,debugging%20system%2C%20making%20stepping%20through%20firmware%20straightforward.)
[11] https://google.github.io/comprehensive-rust/bare-metal/microcontrollers/probe-rs.html
[12] [https://www.eevblog.com/forum/microcontrollers/rust-tools-and-resources-for-embedded/](https://www.eevblog.com/forum/microcontrollers/rust-tools-and-resources-for-embedded/#:~:text=probe%2Drs%2Ddebugger:%20a%20vscode%20extension%20that%20allows%20seamless,and%20how%20the%20can%20be%20automatically%20saved).)
[13] [https://dbtips.substack.com/p/get-the-ultimate-developer-experience](https://dbtips.substack.com/p/get-the-ultimate-developer-experience#:~:text=I%20am%20a%20big%20fan%20of%20the,latter%20will%20write%20pre%2Dcommit%20configuration%20to%20the)
[14] [https://github.com/maziac/DeZog](https://github.com/maziac/DeZog#:~:text=All%20of%20these%20extensions%20can%20be%20easily%20installed%20directly%20from%20the%20marketplace.)
[15] https://marketplace.visualstudio.com/items?itemName=marus25.cortex-debug
[16] https://github.com/Marus/cortex-debug
[17] https://github.com/probe-rs/cargo-embed/issues/169
[18] https://embedded-trainings.ferrous-systems.com/gdb

[jakobjung10]

Thanks for your response!
I actually use the probe-rs extension that you mentioned but it tends to be buggy sometimes, so i looked for an alternative...