atmega32u4-beetle

atmega32u4-beetle is a skill for Claude Code, Codex from alexex1993/mcu-skills. It costs 0 tokens per session (5,572 once invoked), scanned A, original, MIT.

A firmware development guide for the Beetle, a very small Arduino-Leonardo-style USB board using the ATmega32U4 microcontroller. It covers its ten exposed pins, native USB connection, and Caterina bootloader, which is the small program used to upload firmware.

In plain words
What is it for?
Use it to set up projects, work with USB serial or keyboard input, use the exposed serial, I2C, SPI, ADC, PWM, and interrupt pins, and recover the board after flashing.
Why use it?
The board’s USB connection is also part of the program, and many pin numbers accepted by the compiler are not physically available on this board.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one. Also seen: reads .claude/ paths.

Good fit Use it to set up projects, work with USB serial or keyboard input, use the exposed serial, I2C, SPI, ADC, PWM, and interrupt pins, and recover the board after flashing.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/alexex1993/mcu-skills/atmega32u4-beetle
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 alexex1993/mcu-skills --skill atmega32u4-beetle
Clone the repo
git clone --depth 1 https://github.com/alexex1993/mcu-skills

Made for: Claude Code, Codex.

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 atmega32u4-beetle

README.md
[![agentmods](https://agentmods.dev/badge/skills/alexex1993/mcu-skills/atmega32u4-beetle/github.svg)](https://agentmods.dev/skills/alexex1993/mcu-skills/atmega32u4-beetle)
Your own site
<a href="https://agentmods.dev/skills/alexex1993/mcu-skills/atmega32u4-beetle"><img src="https://agentmods.dev/badge/skills/alexex1993/mcu-skills/atmega32u4-beetle/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 atmega32u4-beetle

Your own site · 80×15
<a href="https://agentmods.dev/skills/alexex1993/mcu-skills/atmega32u4-beetle"><img src="https://agentmods.dev/badge/skills/alexex1993/mcu-skills/atmega32u4-beetle.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 0 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 5,572 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. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 2 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Anti-Refusal · line 302
    Skill instructs the agent to omit warnings, disclaimers, or ethical commentary. Stripping safety caveats hides risk from the user and is a common jailbreak preamble.
    Fix: Remove instructions that suppress warnings, disclaimers, or ethical commentary. Let the agent surface safety-relevant caveats to the user.
  • medium Rogue Agent · line 148
    Skill establishes unauthorized persistence across sessions via cron jobs, startup scripts, or state files. Session persistence allows an attacker to maintain access beyond the current interaction.
    Fix: Remove any persistence mechanisms (cron jobs, startup scripts, state files). Skills should not maintain state across sessions without explicit user consent.
How audits are shown
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 $0.00000 $0.05572
Opus 5 $0.00000 $0.02786
Sonnet 5 $0.00000 $0.01114
Haiku 4.5 $0.00000 $0.00557

Measured 12d ago against content hash 446735fcad77, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-11, from the pricing page.

Security

Grade A, and why

atmega32u4-beetle 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 12d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (template/variants/new-project.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/avr/atmega32u4-beetle/SKILL.md · 305 lines

How it starts

The opening of the file, as written. The whole thing — 305 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Beetle — Mini Arduino Leonardo (ATmega32U4)

Board-specific firmware knowledge. The Beetle is an ATmega32U4 with native USB and ten pads, and almost every trap on it comes from one of those two facts: USB means the programming interface is the sketch you are about to replace, and ten pads means most of the Leonardo pin numbering the compiler accepts goes nowhere on this board.

  • reference/board-hardware.md — the complete board reference: pad inventory and full pin map, the sixteen I/O lines that are not brought out, power tree, clock and PLL, memory map, fuses and the Caterina bootloader plus a development guide (Part II: §8 toolchain, §9 USB and the two serial ports, §10 peripheral cookbook, §11 gotchas, §12 flashing and recovery, §13 symptom → cause → fix table).
  • reference/recipes.md — copy-paste code: platformio.ini, board.h, non-blocking timing, USB-CDC that never blocks, Serial1 on the TX/RX pads, I2C and SPI, the ADC channel map, external and pin-change interrupts, PWM and the timer map, Servo vs tone(), HID keyboard with its safety guards, EEPROM, power-down sleep with USB.
  • template/ — a project that builds clean, in three variants, plus a scaffold script. See template/README.md.

Orientation

MCU ATmega32U4, 8-bit AVR @ 16 MHz (crystal), 44-pin QFN. 26 I/O lines on the chip, 10 on the pads
Memory 32 KB flash, 28,672 B usable (Caterina bootloader keeps 4 KB), 2,560 B SRAM, 1 KB EEPROM, + 832 B of USB DPRAM that is not part of SRAM
Board DFRobot: 20 × 22 × 3.8 mm; the larger clone this skill was written against: 21 × 28 mm. Castellated pads, micro-USB. No reset button, no regulator, no VIN, no 3V3
Exposed pads RX(D0) TX(D1) SDA(D2) SCL(D3) 9 10 11 A0 A1 A2 + + (VCC) and - (GND) — DFRobot's own pad↔pin table
LED D13 = PC7, on = HIGH, no pad. DFRobot advertise a "magic light blue soft BLINK indicator" — the blue LED is D13
PWM 4 pads: D3, D11 on Timer0 (the millis() timer, ~977 Hz) · D9, D10 on Timer1 (the Servo timer, ~490 Hz)
ADC 5 × 10-bit: A0 (PF7/ADC7), A1 (PF6/ADC6), A2 (PF5/ADC5), and D9 = A9 (ADC12), D10 = A10 (ADC13)
Interrupts 4 external: D3→INT0, D2→INT1, D0→INT2, D1→INT3 · pin-change on D9/D10/D11 (PCINT5/6/7)
USB Native, on-chip. Serial = USB CDC (no baud rate). HID keyboard/mouse/joystick supported
UART Serial1 on TX/RX (D1/D0) — a genuinely free hardware UART, unlike on an Uno/Nano
I2C / SPI SDA=D2, SCL=D3 (SCL doubles as a PWM pad) · SPI on unlabelled test pads: MISO=D14/PB3, SCK=D15/PB1, MOSI=D16/PB2, SS=D17/PB0
Power 4.5–5 V reliable · 3–4.5 V "may work, not guaranteed" · 6 V destroys it (DFRobot). + is unregulated. Motor/relay loads need ≥ 10 µF and their own supply feed
Debug No SWD/JTAG in practice — the JTAG pins are A0–A3 and the Arduino fuse set disables them. 6-dot ICSP pad array on the back = SPI + RESET
Toolchain PlatformIO 6.1 + atmelavr 5.3.0 + Arduino AVR core, board = leonardo (there is no beetle board in PlatformIO)

Read the full file on GitHub · 305 lines

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. 12d ago First seen · 305 lines · 0 tokens per session scan A 446735fcad77

Subscribe to this mod's changes

atmega32u4-beetle is a skill published in the GitHub repository alexex1993/mcu-skills (17 stars, last pushed yesterday), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 5,572 tokens. 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 2026-08-30.

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