mcp210x-uart

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, GPIO port config, baud rate tables, udev rules, and device locking — through natural language in Claude Code.

Built on FastMCP with Python ctypes bindings to all 45 functions in Silicon Labs' native libcp210xmanufacturing library. Covers the full CP210x family: CP2101, CP2102, CP2102N, CP2103, CP2104, CP2105, CP2108, and CP2109.

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.

Tools

Read-only (no confirmation)

Tool	Description
list_devices	List all connected CP210x devices
get_device_info	Full device details — part number, VID/PID, strings, power, lock state, firmware version (CP2102N), flush config, device mode
get_firmware_version	Firmware version (CP2102N only)
get_flush_buffer_config	Flush buffer configuration (CP2104/CP2105/CP2108)
get_device_mode	Device mode — ECI/SCI assignment (CP2105 only)
get_interface_string	USB interface string (CP2105/CP2108 only)
get_baud_rate_config	Baud rate alias table (32 entries)
get_port_config	GPIO port configuration (auto-detects CP2103/4/5/8)
get_raw_config	Raw EPROM configuration blob (hex string)
create_hex_file	Dump device config to Intel HEX file
reset_device	USB disconnect/reconnect to apply changes

Normal writes (elicitation → fallback to proceed)

Tool	Description
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
set_device_version	Set device version (bcdDevice field)
set_interface_string	Set USB interface string (CP2105/CP2108 only)
set_flush_buffer_config	Set flush buffer configuration (CP2104/CP2105/CP2108)
set_device_mode	Set device mode (CP2105 only)
set_baud_rate_config	Set full 32-entry baud rate alias table
set_baud_rate_alias	Modify a single baud rate alias entry (read-modify-write)
set_port_config	Set GPIO port configuration (auto-detects CP2103/4/5/8)
setup_udev_rule	Generate and install a udev rule for a stable /dev/ symlink

Strict writes (elicitation required — hard-refuses without it)

Tool	Description
set_vid	Set USB Vendor ID (can break driver matching)
set_pid	Set USB Product ID (can break driver matching)
set_raw_config	Write raw configuration blob to EPROM
update_firmware	Update device firmware (CP2102N only)
lock_device	Permanently freeze device configuration

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:

Tier	Behavior	Tools
None	No confirmation	All get_*, list_devices, reset_device, create_hex_file
Normal	Elicitation if client supports it; proceeds otherwise	String setters, power, baud config, port config, setup_udev_rule
Strict	Elicitation required; returns error without it	set_vid, set_pid, set_raw_config, update_firmware, lock_device

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

Part-number support

Different CP210x parts expose different features. The server auto-gates tools to supported parts:

Feature	Supported parts
Core (strings, power, baud)	All CP210x
Flush buffer config	CP2104, CP2105, CP2108
Device mode	CP2105
Interface strings	CP2105, CP2108
Port config	CP2103, CP2104
Dual port config	CP2105
Quad port config	CP2108
Firmware version/update	CP2102N

Requirements

• Linux x86_64
• libcp210xmanufacturing.so — Silicon Labs CP210x manufacturing library
• Python 3.10+
• uv

Installation

1. Native library

Arch Linux (AUR package included):

cd aur/cp210xmanufacturing
makepkg -si

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

From source:

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

uv tool install .

3. Claude Code

claude mcp add cp210x -- uvx mcp210x-uart

For development (runs from source):

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

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-uart/
├── src/mcp210x_uart/
│   ├── server.py          # FastMCP tool definitions, elicitation, part-number dispatch
│   ├── bindings.py        # ctypes: structs, prototypes, bitmask helpers, device wrapper
│   └── __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, GPIO, baud tables). For serial communication (sending/receiving data over UART), use mcserial.

Reference

• CP2102 Datasheet
• AN721: Device Customization Guide — source for libcp210xmanufacturing
• AN197: Serial Communication Guide

License

MIT