# RP2040-ETH Documentation

## Overview

The Waveshare RP2040-ETH is a compact microcontroller board that combines the Raspberry Pi RP2040 chip with built-in Ethernet connectivity. It provides a powerful dual-core processor with integrated networking capabilities in a small form factor.

## Hardware Specifications

### Processor
- **Chip**: Dual-core Arm Cortex M0+ processor
- **Clock Speed**: Flexible clock up to 133 MHz
- **Memory**: 264KB SRAM
- **Storage**: 4MB onboard Flash memory (W25Q32JVSSIQ NOR-Flash)

### Ethernet
- **Ethernet Chip**: CH9120 with integrated TCP/IP protocol stack
- **Capabilities**: 
  - TCP Server/Client modes
  - UDP Server/Client modes
- **Connector**: RJ45 Ethernet port

### I/O and Interfaces
- **GPIO**: 14 multi-function GPIO pins
- **USB**: Type-C connector (USB 1.1 host/device support)
- **Special Features**:
  - 8 Programmable I/O (PIO) state machines
  - Temperature sensor
  - Castellated module design for board integration
  - Compatible with some Pico HATs

### Power
- **Regulator**: RT9013-33GB 500mA Low Dropout LDO
- **Programming**: Drag-and-drop via USB mass storage

## Programming the RP2040-ETH

### Development Options
- C/C++ SDK
- MicroPython
- Arduino IDE

### What We've Learned

From our WS2812 LED control implementation:

1. **PIO Usage**: The RP2040's PIO (Programmable I/O) is excellent for timing-critical operations like WS2812 LED control. We used PIO0 with state machine 0 to generate precise timing signals.

2. **Clock Configuration**: The default system clock works well for most applications. We commented out `set_sys_clock_48()` as it wasn't necessary for our WS2812 implementation.

3. **Pin Mapping**: GPIO 25 was used for WS2812 data output in our example, demonstrating the flexibility of pin assignment on the RP2040.

4. **Timing Precision**: The PIO handles the 800kHz timing requirement of WS2812 LEDs perfectly, showing the RP2040's capability for real-time signal generation.

5. **Memory Efficiency**: With 264KB of SRAM, there's plenty of room for complex applications beyond simple LED control.

### Code Structure Example

Our WS2812 implementation demonstrates key RP2040 programming patterns:

```c
// PIO initialization
PIO pio = pio0;
int sm = 0;
uint offset = pio_add_program(pio, &ws2812_program);
ws2812_program_init(pio, sm, offset, 25, 800000, true);

// Color data formatting (GRB format for WS2812)
uint32_t mask = (green << 16) | (red << 8) | (blue << 0);
put_pixel(mask);
```

### Key Takeaways

1. **Hardware Abstraction**: The Pico SDK provides excellent hardware abstraction layers, making it easy to work with complex peripherals.

2. **PIO Power**: The programmable I/O blocks are one of the RP2040's strongest features, enabling precise timing without CPU intervention.

3. **Development Workflow**: The USB mass storage programming mode makes development iteration very fast - just drag and drop the UF2 file.

4. **Ethernet Integration**: While our example doesn't use Ethernet, the CH9120 chip provides a straightforward path to network connectivity without complex TCP/IP stack implementation.

## Future Considerations

- The Ethernet functionality via CH9120 opens possibilities for IoT applications
- The dual-core processor allows for concurrent tasks (e.g., LED animation on one core, network communication on the other)
- The castellated edges make this board ideal for integration into custom PCBs
- PIO state machines can be used for various protocols beyond WS2812 (SPI, I2C variants, custom protocols)