---
name: bridge
description: Arduino Bridge — the RPC layer that lets Python on the Uno Q's Linux side (MPU) call functions on the Arduino sketch (MCU) and vice-versa. Load this before any project that combines a Python program with an Arduino sketch, or asks how to send data between the Linux side and the sketch.
---

# Bridge — Inter-Processor RPC on the Uno Q

The Uno Q is two computers on one board:

- **MPU** (QRB2210, Debian Linux) — Python, web servers, AI models, OpenCV, Wi-Fi.
- **MCU** (STM32U585, Zephyr + Arduino) — `.ino` sketches; owns every Arduino
  header pin (digital, PWM, ADC, I²C, SPI, UART, CAN).

**Bridge** is Arduino's software RPC layer so either side can call the other.
The MCU has **no Wi-Fi and no Linux**; the MPU has **no direct Arduino pins**. Use
Bridge whenever a project needs *both* sides.

## When to use Bridge

| Scenario | Why |
|---|---|
| Python reads a sensor wired to A0 | MCU owns the pin → Python calls the MCU |
| Sketch needs internet/weather data | MCU has no Wi-Fi → MCU calls the MPU |
| An AI model on Linux drives an LED | Python runs the model → calls the MCU |
| Sketch streams data to a web dashboard | MCU samples → MPU serves HTTP/WebSocket |

## Two ways to reach the MCU from ZeroClaw

1. **Runtime GPIO via the deployed Bridge app** — use the `gpio_read` / `gpio_write`
   tools. These talk to the uno-q-bridge app (TCP :9999) that must already be
   running on the board (`zeroclaw peripheral setup-uno-q` deploys it). Good for
   toggling pins on a sketch that is already flashed.
2. **Flash a whole sketch** — use `uno_q_flash` (see the `flashing` skill) to
   compile and program a full `.ino`, including one that `#include <Bridge.h>` and
   exposes its own RPC services.

## Sketch side (MCU)

```cpp
#include <Bridge.h>
void setup() { Bridge.begin(); }
void loop()  { /* expose services / handle calls */ }
```

## Pitfalls

- The MCU has **no Wi-Fi peripheral** — `#include <WiFi.h>` will not compile for
  `arduino:zephyr:unoq`. Network access is the MPU's job, reached via Bridge.
- `gpio_read`/`gpio_write` require the bridge app running; if they error with a
  connection failure, the app isn't up.