# Raspberry Pi Pico W – Minimal Wi-Fi UDP Example (Arch Linux)

## Authorship

This document was generated using ChatGPT (OpenAI), version 5.2.
It has not been independently reviewed or validated yet.

## Purpose

Minimal Pico W Wi-Fi example using the Arch Linux packaged Pico SDK.
Goal: clean build, no hidden assumptions, raw lwIP usage.

---

## Environment

* Arch Linux
* `pico-sdk` from `/usr/share/pico-sdk`
* Board: Pico W
* Toolchain: `arm-none-eabi-gcc`
* lwIP in `NO_SYS` mode
* Driver: `pico_cyw43_arch_lwip_poll`

---

Add the following sections.

---

## Build

```sh
mkdir build
cd build
cmake ..
make -j
```

Explanation:

* `cmake ..` configures the project and generates build files.
* `make -j` builds using all available CPU cores.
* After configuration, normal source changes require only `make -j`.
* If `CMakeLists.txt` changes, delete the `build/` directory and run `cmake` again.

The resulting firmware file:

```
build/pico_w_udp_client.uf2
```

---

## Flash

```sh
picotool load -f pico_w_udp_client.uf2
```

This writes the UF2 image to the Pico W over USB (device must be in BOOTSEL mode or rebooted via picotool).

---

## Runtime Behavior

After flashing and reset:

1. The Pico W connects to the configured Wi-Fi network.
2. Once DHCP assigns an IP address, the onboard LED turns on.
3. The device begins sending periodic `hello world` UDP messages to the configured destination IP address.


## CMake Configuration

Board is selected in `CMakeLists.txt`:

```cmake
set(PICO_BOARD pico_w)
include(pico_sdk_import.cmake)
```

Wi-Fi credentials are kept outside the main source tree:

```cmake
target_include_directories(pico_w_udp_client PRIVATE
	${CMAKE_CURRENT_LIST_DIR}
	${CMAKE_CURRENT_LIST_DIR}/../secrets
)
```

Example usage:

```c
#include "secrets/fra.h"
```

This keeps credentials separate from firmware logic.

---

## Networking Model

* lwIP raw API (UDP)
* `NO_SYS = 1`
* Explicit polling via `cyw43_arch_poll()`
* Project-local `lwipopts.h`

No sockets, no netconn, no `sys_arch`, no background threads.

---

## Key Points

* Arch SDK requires providing your own `lwipopts.h`.
* Sockets require `NO_SYS = 0` and a `sys_arch` implementation — not used here.
* Raw API is the simplest and fully self-contained option.
* TCP/UDP framing must be handled at application level.

---

## Result

✔ Builds cleanly
✔ Pico W connects to Wi-Fi
✔ UDP packets transmitted
✔ Deterministic configuration