Multi-Device Setup

MCP/U supports connecting multiple devices simultaneously. Each device gets a unique ID that’s used to prefix all its tools, preventing name collisions.

Device Configuration Format

The DEVICES environment variable accepts a comma-separated list of devices:

Transport	Format	Example
Serial	`id:port:baud`	`robot:/dev/ttyUSB0:115200`
TCP	`id:host:port:tcp`	`sensor:192.168.1.42:3000:tcp`

Examples

# Two serial devices
DEVICES=robot:/dev/ttyUSB0:115200,display:/dev/ttyACM0:115200

# Serial + TCP mixed
DEVICES=robot:/dev/ttyUSB0:115200,sensor:192.168.1.42:3000:tcp

# Multiple TCP devices
DEVICES=esp1:192.168.1.10:3000:tcp,esp2:192.168.1.11:3000:tcp

Tool Namespacing

When multiple devices are connected, tool names are prefixed with the device ID:

Scenario	Tool name format	Example
Single device	`{tool_name}`	`gpio_write`
Multiple devices	`{device_id}__{tool_name}`	`robot__gpio_write`

So if you have a robot device and a display device:

robot__gpio_write
robot__hello
display__gpio_write
display__show_text

Configuration Examples

Serial + TCP mixed:

{
  "mcpServers": {
    "mcpu": {
      "command": "npx",
      "args": ["mcpu-client"],
      "env": {
        "DEVICES": "robot:/dev/ttyUSB0:115200,sensor:192.168.1.42:3000:tcp"
      }
    }
  }
}

Config file location:

Linux: ~/.config/claude/claude_desktop_config.json
macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
Windows: %APPDATA%\Claude\claude_desktop_config.json

claude mcp add mcpu -e DEVICES=robot:/dev/ttyUSB0:115200,sensor:192.168.1.42:3000:tcp -- npx mcpu-client

Edit ~/.gemini/settings.json:

{
  "mcpServers": {
    "mcpu": {
      "command": "npx",
      "args": ["mcpu-client"],
      "env": {
        "DEVICES": "robot:/dev/ttyUSB0:115200,sensor:192.168.1.42:3000:tcp"
      }
    }
  }
}

Edit opencode.json:

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "mcpu": {
      "type": "local",
      "command": ["npx", "mcpu-client"],
      "enabled": true,
      "environment": {
        "DEVICES": "robot:/dev/ttyUSB0:115200,sensor:192.168.1.42:3000:tcp"
      }
    }
  }
}

Practical Examples

Robot Arm + Display

Imagine a robot arm on /dev/ttyUSB0 and an OLED display on /dev/ttyACM0:

DEVICES=arm:/dev/ttyUSB0:115200,display:/dev/ttyACM0:115200

Tools available:

arm__gpio_write
arm__adc_read
arm__move_servo
display__show_text
display__clear

Weather Station + Gateway

A weather sensor connected via WiFi and a serial gateway:

DEVICES=sensor:192.168.1.50:3000:tcp,gateway:/dev/ttyUSB0:115200

Setting Device IDs in Firmware

When you create your McpDevice, give it a unique ID that matches your configuration:

McpDevice mcp("robot", "1.0.0");  // This becomes the device ID

Make sure the ID in your firmware matches the ID in your DEVICES string!

Best Practices

Use Descriptive IDs

Choose IDs that describe the device: robot, display, sensor, weather-station — not dev1, dev2.

Consistent Naming

Keep the same ID across restarts. If you restart and the ID changes, your agent’s tool calls will break.

Mix Freely

Serial and TCP can be combined in any configuration. There’s no limit on mixing.

Check Tool List

Use MCP Inspector or call list_tools to verify all devices are connected and tools are properly namespaced.

Next Steps

Connect via Serial — single serial device
Connect via WiFi TCP — single TCP device
Debug Connection Issues — troubleshooting