pico-w-experiments/basic-udp/readme.md

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.

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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

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Add the following sections.

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Build

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

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Flash

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).

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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:

set(PICO_BOARD pico_w)
include(pico_sdk_import.cmake)

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

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

Example usage:

#include "secrets/fra.h"

This keeps credentials separate from firmware logic.

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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.

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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.

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Result

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