openocd-mcp-debug

name	openocd-mcp-debug
description	[Mandatory develop-verify loop] Embedded firmware debug, flash, and RTT real-time log verification expert. When asked to change code, add features, fix bugs, or monitor runtime, must follow the "modify code → build → flash → RTT verify → analyze → fix → re-verify" closed loop until the task passes verification. Based on openocd-mcp MCP server, debugs STM32/ARM Cortex-M targets via OpenOCD + GDB.
allowed-tools	["Read","Write","Edit","Bash","Grep","Glob","mcp_openocd-mcp_set_project","mcp_openocd-mcp_refresh_debug_targets","mcp_openocd-mcp_flash_download","mcp_openocd-mcp_debug_start","mcp_openocd-mcp_debug_attach","mcp_openocd-mcp_debug_stop","mcp_openocd-mcp_debug_continue","mcp_openocd-mcp_debug_interrupt","mcp_openocd-mcp_debug_command","mcp_openocd-mcp_debug_state","mcp_openocd-mcp_debug_status","mcp_openocd-mcp_get_runtime_config","mcp_openocd-mcp_read_rtt","mcp_openocd-mcp_shutdown"]

openocd-mcp Embedded Debug Skill

Project Overview

openocd-mcp is a fastmcp-based MCP server that wraps OpenOCD flashing and GDB debugging workflows into AI-callable tools. It reuses the project's existing .vscode/launch.json as the debug target source, requiring no extra configuration.

Property	Description
Repository	D:\GitHub_Repository\openocd-mcp
Installation	uv tool install . or uv tool install git+https://github.com/luiox/openocd-mcp.git
Run mode	stdio (default, VS Code MCP) / SSE (--sse --host 127.0.0.1 --port 9000)
Protocol	GDB/MI2 async protocol (--interpreter=mi2), event-driven, no polling
Dependencies	OpenOCD + arm-none-eabi-gdb
Platforms	Windows / Linux / macOS

Core Architecture

AI Client → MCP Protocol → openocd-mcp
                               ├── ProjectConfigManager (parses launch.json)
                               ├── OpenOCDController (start/stop OpenOCD process)
                               ├── GDBMISession (MI2 async protocol communication)
                               ├── RTTClient (real-time log reading)
                               └── DebugSessionManager (coordinates lifecycle)

MCP Tool Complete Reference

All tools return strings by default. On failure, the response starts with "Error: ".

Project & Configuration

Tool	Description	Typical Usage
set_project(project_dir)	Load project .vscode/launch.json	set_project(project_dir="d:/path/to/project")
refresh_debug_targets()	Reload launch.json configurations	Use after modifying launch.json
get_runtime_config()	View current OpenOCD/GDB paths and their sources	Use when troubleshooting path issues

Flash & Debug Lifecycle

Tool	Description	Typical Usage
flash_download(config_name, firmware_path?)	One-time firmware flash (no debug session)	flash_download(config_name="Launch (DAP)")
debug_start(config_name, firmware_path?)	Start a debug session	debug_start(config_name="Launch (DAP)")
debug_stop()	Stop the debug session	debug_stop()

Runtime Control

Tool	Description	Key Notes
debug_continue()	Resume target execution	Async return, non-blocking. GDB remains responsive while target is running
debug_interrupt()	Pause target	Uses GDB/MI -exec-interrupt. On Windows, auto-fallback to OpenOCD telnet halt
debug_command(command)	Execute arbitrary GDB command	"continue"/"interrupt" are auto-mapped to MI async commands
debug_state()	Query target state	Returns `{"state": "running"
debug_status()	Get full session info	Includes PID, RTT connection status, etc.

Data Reading

Tool	Description	Typical Usage
read_rtt(max_lines=10)	Read RTT real-time logs	read_rtt(max_lines=20)
debug_command(command)	Read registers/variables	debug_command("info registers") / debug_command("print x")

Server Control

Tool	Description	Typical Usage
shutdown()	Gracefully exit the MCP server	Call before reinstalling to release file locks

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⚠️ Mandatory workflow: When asked to add features, fix bugs, or monitor runtime, you must follow the "Develop-Verify Loop" below. Do not skip verification steps and report completion directly.

---

Mandatory Develop-Verify Loop

This is the core workflow of this skill. Regardless of task type (new feature, bug fix, debug analysis), you must follow this closed loop.

Loop Overview

flowchart TD
    A[Understand requirements] --> B[Modify/write code]
    B --> C[Build firmware]
    C --> D[Flash & start debug]
    D --> E[Run program + RTT monitor]
    E --> F{Does result match expectations?}
    F -->|Yes| G[Stop debug]
    F -->|No| H[Analyze RTT / GDB output]
    H --> I[Diagnose root cause]
    I --> B
    G --> J[Report completion]

Step-by-Step Instructions

Step 1: Understand Requirements & Plan

• Identify the code files to modify (driver/HAL/application layer)
• Define verification criteria: what logs should appear in RTT? What behavior changes?

Step 2: Modify Code

• Modify source files according to requirements
• Document changes for later verification reference

Step 3: Build Firmware 🔨

xmake f -p cross -a arm -m debug
xmake build weather_station

• Build must succeed before proceeding to the next step
• Build failure → fix compilation errors → rebuild

Step 4: Flash & Start Debug 🚀

set_project(project_dir="d:/GitHub_Repository/weather-station")
debug_start(config_name="Launch weather_station (DAP)")

• Confirm output includes RTT connected on port 8888
• Confirm output includes Stopped at main (breakpoint hit)

Step 5: Run + RTT Verification 📡

debug_continue()
# Wait sufficient time for code logic to execute (varies by scenario: 2s/10s/20s)
debug_interrupt()
read_rtt(max_lines=20)

Step 6: Analyze Verification Results 🔍

• Expected behavior appears in RTT logs → verification passed → stop debug → report completion
• RTT logs abnormal or no output → analyze root cause:
  • Code logic error → go back to Step 2
  • Build issue → go back to Step 3
  • Debug issue → check GDB/RTT status

Step 7: Report Completion

• Summarize: which files were changed, what was verified, key RTT output
• Confirm all task requirements are met

Verification Criteria for Four Common Task Types

Task Type	Core Verification Method	Expected RTT Output Example
New feature (e.g., adding sensor driver)	Observe if new sensor data logs appear in RTT	[INFO] ACQ: ... NEW_SENSOR=123 ...
Bug fix	Confirm the bug-related error disappears, normal logs appear	Original [ERROR] xxx failed disappears, [INFO] xxx OK appears
Logic change (e.g., adjusting acquisition period)	Verify RTT log interval/behavior matches new logic	Logs change from every 2s to every 5s, etc.
Runtime monitoring (e.g., stability analysis)	Check RTT for anomalies after extended runtime	30+ consecutive ACQ records with no errors

Complete Example: Self-Verification After Adding a Feature

User: "Add a wind speed sensor alarm to weather-station"

Agent executes the loop:

① Understand requirements → Need to add threshold alarm in anemometer driver
② Modify code → Edit src/driver/anemometer.c
③ Build → xmake build weather_station (success)
④ Flash & debug → set_project + debug_start
⑤ Run & verify → debug_continue → wait 10s → debug_interrupt → read_rtt
⑥ Analyze → RTT shows "⚠️ Wind speed exceeded: 18.5m/s"
               → Matches expectation ✅
⑦ Report completion → Summarize changes and verification results

If RTT shows no alarm → go back to ② fix logic → ③~⑥ re-verify

Complete Example: Self-Verification After Bug Fix

User: "LoRa sending keeps failing, help me check"

Agent executes the loop:

① Understand requirements → LoRa send returns error, need to troubleshoot
② Locate code → Find timeout handling issue in lora_port.c
③ Modify code → Fix timeout retry logic
④ Build → Success
⑤ Flash & verify → debug_continue → wait 10s → read_rtt
⑥ Analyze → RTT shows "[INFO] LoRa send OK (46B)"
               → Previously was "[ERROR] LoRa send failed"
               → Bug fixed ✅
⑦ Report completion → Explain root cause and fix

If failure still appears → Continue analyzing driver code → Fix → Re-flash & verify

RTT Output Quick Reference

RTT Log Pattern	Meaning
[INFO] ACQ: T=.. H=.. P=..	Normal data acquisition (every ~2s)
[ERROR] ... failed	Sensor or communication failure, needs troubleshooting
[INFO] System ready	System initialization complete
[INFO] LoRa send OK	LoRa send successful
No RTT output	Check RTT connection; or firmware hasn't reached log output point
rtt: Control block not available	RTT control block not initialized (log_init() not called)

RTT Log Details

RTT works through an automatic startup process:

debug_start → GDB monitor rtt server start 8888 0
            → GDB print &_SEGGER_RTT (get control block address)
            → GDB monitor rtt setup <address> 1024
            → GDB monitor rtt start
            → TCP connection 127.0.0.1:8888 ← RTTClient

Key points:

• Firmware must include SEGGER RTT implementation (SEGGER_RTT_Conf.h, SEGGER_RTT.c)
• RTT initialization occurs after log_init(), rtt setup pre-sets address but doesn't block
• RTT failure does not block the debug session; it degrades silently
• Check debug_status() rtt_connected field to determine if RTT is working
• Default port 8888, changeable via --rtt-port / RTT_PORT env var / config.json rtt_port field

Configuration

Parameter priority: CLI args > Environment variables > config.json > Built-in defaults

config.json (workspace root)

{
  "openocd_path": "C:/Program Files (x86)/xpack-openocd-.../bin/openocd.exe",
  "gdb_path": "C:/Program Files (x86)/Arm GNU Toolchain/.../bin/arm-none-eabi-gdb.exe",
  "openocd_scripts": "",
  "rtt_port": 8888,
  "adapter_speed": 1000
}

Environment Variables

Variable	Purpose
OPENOCD_PATH	OpenOCD executable path
GDB_PATH	GDB executable path
OPENOCD_SCRIPTS	OpenOCD scripts directory (-s argument)
RTT_PORT	RTT server port

CLI Arguments

openocd-mcp --openocd-path openocd --gdb-path arm-none-eabi-gdb --rtt-port 8888
openocd-mcp --sse --host 127.0.0.1 --port 9000  # SSE/HTTP mode

VS Code MCP Configuration (.vscode/mcp.json)

{
  "servers": {
    "openocd-mcp": {
      "type": "stdio",
      "command": "openocd-mcp",
      "args": [],
      "cwd": "${workspaceFolder}"
    }
  }
}

Platform Differences

Windows

• Interrupt mechanism: GDB/MI -exec-interrupt pipe interrupt is unreliable; auto-fallback to OpenOCD telnet halt (connect to 127.0.0.1:4444, send halt\n)
• Paths: OpenOCD requires forward slashes; code handles this automatically
• Process management: GDB launched with CREATE_NEW_PROCESS_GROUP flag

Unix (Linux/macOS)

• Interrupt mechanism: GDB/MI -exec-interrupt works reliably
• MI method preferred, telnet fallback as degradation option

Fixing "MCP Tool Disabled by the User" Error

If you see ERROR while calling tool: Tool mcp_openocd-mcp_xxx is currently disabled by the user:

# 1. Clear MCP cache and pre-approve tools
python -c "
import sqlite3, json
ws = sqlite3.connect('C:/Users/xxx/AppData/Roaming/Code/User/workspaceStorage/<workspace_id>/state.vscdb')
for key in ['mcpToolCache', 'mcp.extCachedServers']:
    ws.execute('DELETE FROM ItemTable WHERE key = ?', (key,))
tools = ['set_project','refresh_debug_targets','flash_download','debug_start','debug_attach','debug_stop',
         'debug_command','debug_continue','debug_interrupt','debug_status','debug_state',
         'get_runtime_config','read_rtt','shutdown']
autoconfirm = {f'mcp_openocd-mcp_{t}': True for t in tools}
ws.execute('INSERT OR REPLACE INTO ItemTable (key, value) VALUES (?, ?)',
           ('chat/autoconfirm', json.dumps(autoconfirm)))
ws.commit(); ws.close()
"
# 2. Reload VS Code window (Ctrl+Shift+P → Developer: Reload Window)

Common Troubleshooting

1. OpenOCD Startup Failure

Error: OpenOCD failed to start: [WinError 2] The system cannot find the specified file.

• Cause: openocd_path in config.json doesn't exist or wrong config file was read
• Diagnosis: Call get_runtime_config() to check the actual path and its source
• Fix: Ensure config.json in workspace root contains the correct path

2. GDB Connection Failure

Error: GDB connection failed: Remote communication error.

• Cause: OpenOCD failed to start GDB server within 15 seconds (port 3333)
• Diagnosis: Check debugger physical connection; check OpenOCD scripts; reduce adapter_speed
• Fix: Add "adapter_speed": 500 to config.json

3. Flash Failure

Error erasing flash with vFlashErase packet

• Cause: SWD clock speed too high, unstable communication
• Fix: Reduce adapter_speed (common stable values: 1000kHz, 500kHz)

4. No RTT Data

RTT: (no new RTT output)

• Cause: Firmware doesn't include SEGGER RTT, or log_init() not called
• Diagnosis: Check rtt_connected in debug_status() result
• Fix: Confirm firmware integrates SEGGER RTT library and calls log_init() at startup

5. debug_interrupt Timeout

Error: GDB command timed out after 30s: -exec-interrupt

• Cause: GDB pipe signal unreliable on Windows
• Diagnosis: OpenOCD telnet halt is already an auto-fallback and shouldn't appear. If still timing out, manually check via telnet:

  python -c "import socket;s=socket.socket();s.settimeout(3);s.connect(('127.0.0.1',4444));s.sendall(b'halt\n');s.close()"
  

6. File Lock Error on Reinstall

error: failed to remove directory ... Scripts: Access denied

• Cause: Old MCP process still running, holding file locks
• Fix: Call shutdown() to stop the current MCP process first, or manually taskkill //F //IM openocd-mcp.exe

Standard MCP Reinstallation Procedure

# 1. Let the current MCP process exit
# Call shutdown() in the AI chat

# 2. Ensure process is terminated (optional)
taskkill //F //IM openocd-mcp.exe

# 3. Update code and reinstall
cd D:/GitHub_Repository/openocd-mcp
git pull  # or after modifying code
uv tool install --reinstall .

# 4. Reload VS Code window
# Ctrl+Shift+P → Developer: Reload Window

Important Notes

1. Single session model: At most one debug session at a time; debug_start auto-stops previous sessions
2. launch.json compatibility: Supports C-style comments and trailing commas (parser auto-cleans)
3. Timeout control: Normal GDB commands 30s timeout, load 120s, flash 180s
4. Path resolution: ${workspaceRoot} and ${workspaceFolder} are auto-replaced with project directory
5. config.json reading: Based on CWD (current working directory), reads CWD/config.json
6. Async continue: debug_continue() returns immediately via MI ^running, doesn't block waiting for target to stop

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Workflow Enforcement Reminder

⚠️ After every code change, you must go through "build → flash → RTT verification" before reporting completion.

⚠️ When verification fails, you must analyze RTT output, diagnose root cause, fix code, and re-verify to form a closed loop.

⚠️ Do not skip verification steps because it "looks fixed." RTT logs are the sole basis for judging task completion.