add seeeduino_xiao_rp2040_neopixel_rainbow example (#94)

boards/seeeduino-xiao-rp2040/Cargo.toml

@@ -21,6 +21,8 @@ embedded-hal.workspace = true
 fugit.workspace = true
 nb.workspace = true
 panic-halt.workspace = true
+smart-leds.workspace = true
+ws2812-pio.workspace = true
 
 [features]
 # This is the set of features we enable by default

boards/seeeduino-xiao-rp2040/examples/seeeduino_xiao_rp2040_neopixel_rainbow.rs

@@ -0,0 +1,108 @@
+//! Rainbow effect color wheel using the onboard NeoPixel on a Seeed XIAO RP2040 board
+//!
+//! This flows smoothly through various colours on the onboard NeoPixel.
+//! Uses the `ws2812_pio` driver to control the NeoPixel, which in turns uses the
+//! RP2040's PIO block.
+#![no_std]
+#![no_main]
+
+use core::iter::once;
+use embedded_hal::delay::DelayNs;
+use panic_halt as _;
+use smart_leds::{brightness, SmartLedsWrite, RGB8};
+
+use seeeduino_xiao_rp2040::{
+    entry,
+    hal::{
+        clocks::{init_clocks_and_plls, Clock},
+        gpio::PinState,
+        pac,
+        pio::PIOExt,
+        timer::Timer,
+        watchdog::Watchdog,
+        Sio,
+    },
+    Pins, XOSC_CRYSTAL_FREQ,
+};
+
+use ws2812_pio::Ws2812;
+
+/// Entry point to our bare-metal application.
+///
+/// The `#[entry]` macro ensures the Cortex-M start-up code calls this function
+/// as soon as all global variables are initialised.
+///
+/// The function configures the RP2040 peripherals, then infinitely cycles the built-in LED colour from red, to green,
+/// to blue and back to red.
+#[entry]
+fn main() -> ! {
+    let mut pac = pac::Peripherals::take().unwrap();
+
+    let mut watchdog = Watchdog::new(pac.WATCHDOG);
+
+    let clocks = init_clocks_and_plls(
+        XOSC_CRYSTAL_FREQ,
+        pac.XOSC,
+        pac.CLOCKS,
+        pac.PLL_SYS,
+        pac.PLL_USB,
+        &mut pac.RESETS,
+        &mut watchdog,
+    )
+    .ok()
+    .unwrap();
+
+    let sio = Sio::new(pac.SIO);
+    let pins = Pins::new(
+        pac.IO_BANK0,
+        pac.PADS_BANK0,
+        sio.gpio_bank0,
+        &mut pac.RESETS,
+    );
+
+    let timer = Timer::new(pac.TIMER, &mut pac.RESETS, &clocks);
+
+    // Turn on neopixel power
+    pins.neopixel_power
+        .into_push_pull_output_in_state(PinState::High);
+
+    // Configure the addressable LED
+    let (mut pio, sm0, _, _, _) = pac.PIO0.split(&mut pac.RESETS);
+    let mut ws = Ws2812::new(
+        // The onboard NeoPixel is attached to GPIO pin #16 on the Waveshare RP2040-Zero.
+        pins.neopixel_data.into_function(),
+        &mut pio,
+        sm0,
+        clocks.peripheral_clock.freq(),
+        timer.count_down(),
+    );
+
+    // Infinite colour wheel loop
+    let mut n: u8 = 128;
+    let mut timer = timer; // rebind to force a copy of the timer
+    loop {
+        ws.write(brightness(once(wheel(n)), 32)).unwrap();
+        n = n.wrapping_add(1);
+
+        timer.delay_ms(25);
+    }
+}
+
+/// Convert a number from `0..=255` to an RGB color triplet.
+///
+/// The colours are a transition from red, to green, to blue and back to red.
+fn wheel(mut wheel_pos: u8) -> RGB8 {
+    wheel_pos = 255 - wheel_pos;
+    if wheel_pos < 85 {
+        // No green in this sector - red and blue only
+        (255 - (wheel_pos * 3), 0, wheel_pos * 3).into()
+    } else if wheel_pos < 170 {
+        // No red in this sector - green and blue only
+        wheel_pos -= 85;
+        (0, wheel_pos * 3, 255 - (wheel_pos * 3)).into()
+    } else {
+        // No blue in this sector - red and green only
+        wheel_pos -= 170;
+        (wheel_pos * 3, 255 - (wheel_pos * 3), 0).into()
+    }
+}