swd-tracer

swd-tracer is a skill for Claude Code from CrossPad/crosspad-mcp. It costs 150 tokens per session (2,757 once invoked), scanned A, original, MIT.

A workflow for tracing and plotting STM32 firmware variables in real time through SWD on a CrossPad r20 board. STM32 is a family of microcontrollers, and SWD is a debugging connection used to inspect running firmware.

In plain words
What is it for?
It is for checking firmware signals on the specified STM32 board through ST-Link and pyOCD, including configuring symbols, starting and stopping traces, and viewing readings.
Why use it?
It provides a defined way to set up or repair the tracing environment and move from diagnosis to live readings and a user interface.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: reads .claude/ paths.

Part of the crosspad plugin — 3 skills, 2 MCP servers shipped together

Good fit It is for checking firmware signals on the specified STM32 board through ST-Link and pyOCD, including configuring symbols, starting and stopping traces, and viewing readings.

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Install with agentmods
npx agentmods add skills/crosspad/crosspad-mcp/swd-tracer
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add CrossPad/crosspad-mcp --skill swd-tracer
Clone the repo
git clone --depth 1 https://github.com/CrossPad/crosspad-mcp

Made for: Claude Code.

Or install crosspad, the plugin that ships this one along with the rest of its 3 skills, 2 MCP servers.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for swd-tracer

README.md
[![agentmods](https://agentmods.dev/badge/skills/crosspad/crosspad-mcp/swd-tracer/github.svg)](https://agentmods.dev/skills/crosspad/crosspad-mcp/swd-tracer)
Your own site
<a href="https://agentmods.dev/skills/crosspad/crosspad-mcp/swd-tracer"><img src="https://agentmods.dev/badge/skills/crosspad/crosspad-mcp/swd-tracer/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for swd-tracer

Your own site · 80×15
<a href="https://agentmods.dev/skills/crosspad/crosspad-mcp/swd-tracer"><img src="https://agentmods.dev/badge/skills/crosspad/crosspad-mcp/swd-tracer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 150 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,757 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00150 $0.02757
Opus 5 $0.00075 $0.01378
Sonnet 5 $0.00030 $0.00551
Haiku 4.5 $0.00015 $0.00276

Measured 9d ago against content hash 7233d4464f27, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

swd-tracer scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

The scan reads SKILL.md. This mod also ships 3 executable files (scripts/detect-env.sh, scripts/install-udev-rules.sh, scripts/setup-venv.sh), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/swd-tracer/SKILL.md · 184 lines

How it starts

The opening of the file, as written. The whole thing — 184 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CrossPad SWD real-time tracer

Live, non-halting plotting of firmware variables read straight from MCU RAM over an ST-Link, à la ST-Studio / CubeMonitor — but driven by the agent. The MCP server already lists which tools exist; this skill encodes how to set the tracer up and drive it, and how to recover when the probe misbehaves.

Target: CrossPad r20 = STM32G0B1xx (Cortex-M0+) firmware in the CrossPad_STM32_r20 repo. Variables are resolved from the Debug ELF DWARF; pyOCD polls their RAM addresses while the core keeps running. (Cortex-M0+ has no ITM/SWO/DWT, so SWO/ITM "printf" is impossible — RAM polling is the mechanism.)

All operations go through one MCP tool, crosspad_trace, via its action: doctor · config_set · symbols · start · add · remove · status · read · save · device_state · ui · stop.

First move: always doctor

crosspad_trace action=doctor

It reports issues[] and whether a probe is connected. Resolve blocking issues (below) before start. If you're unsure what's configured, also run the read-only environment probe:

bash scripts/detect-env.sh

The helper scripts are bundled next to this SKILL.md in scripts/. Resolve them relative to the skill directory — e.g. ~/.claude/skills/swd-tracer/scripts/… (global skill) or <crosspad-mcp>/skills/swd-tracer/scripts/… (repo / plugin).

Configuring the four environments

The tracer needs four things in place. doctor / detect-env.sh tell you which are missing; fix only those.

  1. pyOCD venv — the daemon runs in a Python venv (system Python is usually PEP-668 locked). Create it and point config at it:
    bash scripts/setup-venv.sh
    crosspad_trace action=config_set key=pyocd_python value=$HOME/.local/share/crosspad-mcp/venv/bin/python
    
  2. User config paths — persisted to ~/.config/crosspad-mcp/config.json. Keys: stm_elf_path (the Debug ELF), pyocd_python, probe_serial (optional; only if multiple ST-Links), trace_dir (where .cptrace/CSV go).
    crosspad_trace action=config_set key=stm_elf_path value=<repo>/build/Debug/CrossPad_STM32_r20.elf
    
  3. ST-Link udev rules (Linux) — needed for libusb access without root:
    bash scripts/install-udev-rules.sh   # sudo; then replug the ST-Link
    
  4. Debug ELF with symbols — build it in the firmware repo so DWARF exists:
    cmake --preset Debug && cmake --build build/Debug
    

Read the full file on GitHub · 184 lines

Files

What ships with it

4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 184 lines · 150 tokens per session scan A 7233d4464f27

Subscribe to this mod's changes

swd-tracer is a skill published in the GitHub repository CrossPad/crosspad-mcp (1 stars, last pushed 5d ago), licensed MIT. It adds 150 tokens to every session and 2,757 once invoked, about $0.0007 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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