# mcp210x

It's MCP. It's CP210x. It was right there the whole time.

An MCP server for customizing Silicon Labs CP210x USB-UART bridge devices — product strings, serial numbers, power config, udev rules, and device locking — through natural language in Claude Code.

Built on [FastMCP](https://gofastmcp.com/) with Python ctypes bindings to Silicon Labs' native `libcp210xmanufacturing` library.

## The problem

You plug in three CP2102 boards. They all enumerate as:

```
Bus 001 Device 004: ID 10c4:ea60 Silicon Labs CP2102 USB to UART Bridge Controller
Bus 001 Device 005: ID 10c4:ea60 Silicon Labs CP2102 USB to UART Bridge Controller
Bus 001 Device 006: ID 10c4:ea60 Silicon Labs CP2102 USB to UART Bridge Controller
```

Which one is which? Unplug, replug, guess. `/dev/ttyUSB0` becomes `/dev/ttyUSB2` after a reboot. You write udev rules that match on nothing unique. The Silicon Labs GUI customization tool is 32-bit only and hasn't been updated since 2015.

## The fix

```
> What CP210x devices are connected?

Two devices found:
  [0] RYLR998 0033001104645C0B00001130 (serial: 0001)
  [1] RYLR998 0033001104645C0B00000D27 (serial: 0001)

> Set up a udev rule for device 0 so it always appears at /dev/rylr998-1130
```

Each device gets a unique product string baked into its USB descriptor EPROM. Udev rules match on that string to create stable symlinks. Devices survive reboots, port reordering, and hub changes.

## Features

- **List and inspect** connected CP210x devices (part number, VID/PID, strings, power, lock state)
- **Write USB descriptors** — product string, manufacturer, serial number
- **Configure power** — max current draw, self-powered vs bus-powered
- **Generate udev rules** — stable `/dev/` symlinks based on product string
- **Reset device** — trigger USB re-enumeration after changes
- **Lock device** — permanently freeze configuration (with strict confirmation gate)

## Safety model

CP210x descriptor EPROM is one-time-programmable with limited write cycles. Writes can't be undone. Locks are permanent. The server enforces a tiered confirmation model:

| Operation | Confirmation |
|-----------|-------------|
| Reads | None |
| Writes (strings, power) | MCP elicitation if client supports it; proceeds otherwise |
| Lock | Elicitation **required**; hard-refuses without it |

The lock gate isn't just a warning — it returns an error and does not proceed if the MCP client can't present a confirmation dialog.

## Requirements

- Linux x86_64
- `libcp210xmanufacturing.so` — Silicon Labs CP210x manufacturing library
- Python 3.10+
- [uv](https://docs.astral.sh/uv/)

## Installation

### 1. Native library

**Arch Linux** (AUR package included):

```bash
cd aur/cp210xmanufacturing
makepkg -si
```

This installs the shared library, headers, and udev rules for non-root USB access.

**From source:**

```bash
cd AN721SW/Linux/LibrarySourcePackages/cp210xmanufacturing
make LIB_ARCH=64
sudo make install
sudo ldconfig
```

You'll also need udev rules for non-root device access — copy `aur/cp210xmanufacturing/SiliconLabs.rules` to `/usr/lib/udev/rules.d/` and reload.

### 2. MCP server

```bash
uv tool install .
```

### 3. Claude Code

```bash
claude mcp add cp210x -- uvx mcp210x
```

For development (runs from source):

```bash
claude mcp add cp210x-local -- uv run --directory /path/to/this-repo mcp210x
```

## Tools

| Tool | Description |
|------|-------------|
| `list_devices` | List connected CP210x devices with description and serial |
| `get_device_info` | Full device details — part number, VID/PID, strings, power, lock state |
| `set_product_string` | Write USB product string (max 126 chars) |
| `set_manufacturer_string` | Write USB manufacturer string (max 45 chars) |
| `set_serial_number` | Write USB serial number (max 63 chars) |
| `set_max_power` | Set max USB power draw in mA (0-500, rounded to nearest 2) |
| `set_self_powered` | Toggle self-powered vs bus-powered reporting |
| `reset_device` | USB disconnect/reconnect to apply changes |
| `lock_device` | Permanently freeze device configuration |
| `setup_udev_rule` | Generate and install a udev rule for a stable `/dev/` symlink |

## Architecture

```
Claude Code ──stdio──▶ FastMCP server (server.py)
                              │
                              ▼
                        Python ctypes (bindings.py)
                              │
                              ▼
                    libcp210xmanufacturing.so
                              │
                              ▼
                          libusb ──▶ CP210x device
```

The native library uses **libusb** for device access, separate from the kernel's `cp210x` serial driver. Both coexist — you can read/write UART data over `/dev/ttyUSB0` while customizing USB descriptors through this server.

## Project structure

```
mcp210x/
├── src/mcp210x/
│   ├── server.py          # FastMCP tool definitions and elicitation logic
│   ├── bindings.py        # ctypes wrapper for libcp210xmanufacturing.so
│   └── __init__.py
├── aur/cp210xmanufacturing/
│   ├── PKGBUILD           # Arch Linux package for the native library
│   └── SiliconLabs.rules  # udev rules for non-root USB access
├── AN721SW/               # Silicon Labs toolkit (library source)
├── docs/                  # Datasheets and application notes
└── pyproject.toml
```

## Complementary tools

This server handles **device customization** (USB descriptors, power config). For **serial communication** (sending/receiving data over UART), use [mcserial](https://git.supported.systems/MCP/mcserial).

## Reference

- [CP2102 Datasheet](https://www.silabs.com/documents/public/data-sheets/CP2102-9.pdf)
- [AN721: Device Customization Guide](https://www.silabs.com/documents/public/example-code/AN721SW.zip) — source for `libcp210xmanufacturing`
- [AN197: Serial Communication Guide](https://www.silabs.com/documents/public/application-notes/an197-serial-communications-guide-cp210x.pdf)

## License

MIT