# cp210x-mcp

MCP server for customizing Silicon Labs CP210x USB-UART bridge devices. Read and write USB descriptor strings, power configuration, and device lock state — all through natural language in Claude Code.

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

## Why

CP210x chips (CP2102, CP2102N, CP2104, etc.) store USB descriptor strings in one-time-programmable EPROM. Silicon Labs provides a GUI tool and a C library for customization, but both are clunky to use — especially when managing multiple identical devices that need unique identifiers.

This MCP server lets you customize devices conversationally:

```
> What CP210x devices are connected?
> Change the product string of device 0 to "RYLR998 0033001104645C0B00001130"
> Set up a udev rule so it always appears at /dev/rylr998-1130
```

## 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)
- **Elicitation support** — write operations request confirmation when the MCP client supports it; graceful fallback otherwise. Lock is the exception: it *requires* explicit confirmation and will refuse if elicitation is unavailable.

## Requirements

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

## Installation

### 1. Install the native library

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

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

**From source:**

```bash
# Extract AN721SW toolkit (included in docs/)
cd AN721SW/Linux/LibrarySourcePackages/cp210xmanufacturing
make LIB_ARCH=64
sudo make install
sudo ldconfig
```

The library installs to `/usr/lib/libcp210xmanufacturing.so` and uses libusb to communicate with devices. You'll need udev rules for non-root access — the AUR package installs these automatically, or copy `aur/cp210xmanufacturing/SiliconLabs.rules` to `/usr/lib/udev/rules.d/`.

### 2. Install the MCP server

```bash
uv tool install .
```

### 3. Add to Claude Code

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

Or for development (runs from source):

```bash
claude mcp add cp210x-local -- uv run --directory /path/to/cp2102-uart cp210x-mcp
```

## 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, which is separate from the kernel's `cp210x` serial driver. Both can coexist — you can read/write UART data over `/dev/ttyUSB0` while simultaneously customizing USB descriptors through this server.

### Safety model

CP210x EPROM writes are one-time-programmable with limited write cycles. The server uses a tiered confirmation model:

- **Reads** — no confirmation needed
- **Writes** (strings, power) — requests confirmation via MCP elicitation; falls back to proceeding if the client doesn't support it
- **Lock** — *always* requires elicitation; hard-refuses without it

## Complementary tools

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