Write generic "get me a working Neopixel output pin" code for Gemma M0

gemma_m0_lights/Cargo.toml

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+[package]
+name = "gemma_m0_lights"
+version = "0.1.0"
+authors = ["Tangent 128 <Tangent128@gmail.com>"]
+edition = "2018"
+
+[dependencies]
+cortex-m = { version = "0.5.8", features = ["inline-asm"] }
+embedded-hal = "0.2.2"
+gemma_m0 = "0.2.1"
+lights = { path = "../lights" }
+panic-halt = "0.2"

gemma_m0_lights/src/lib.rs

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+#![no_std]
+
+extern crate cortex_m;
+extern crate embedded_hal;
+extern crate gemma_m0 as hal;
+extern crate panic_halt;
+
+pub use cortex_m::asm::delay;
+pub use hal::entry;
+
+use core::u8;
+use embedded_hal::digital::OutputPin;
+use hal::{
+    clock::GenericClockController,
+    Peripherals
+};
+use lights::{
+    gamma::CorrectedRgb,
+    Lights
+};
+
+pub fn boot() -> impl Lights<Pixel = CorrectedRgb> {
+    let mut peripherals = Peripherals::take().unwrap();
+    let _clock = GenericClockController::with_internal_32kosc(
+        peripherals.GCLK,
+        &mut peripherals.PM,
+        &mut peripherals.SYSCTRL,
+        &mut peripherals.NVMCTRL
+    );
+
+    let mut pins = hal::Pins::new(peripherals.PORT);
+
+    NeopixelLights {
+        out: pins.d1.into_push_pull_output(&mut pins.port)
+    }
+}
+
+// approx. 20ns per clock cycle;
+const ZERO_HIGH_CYCLES: u32 = 11; // smidge above 200ns
+const ONE_HIGH_CYCLES: u32 = 35; // about 700ns
+const DATA_LOW_CYCLES: u32 = 25; // about 500ns
+const LATCH_CYCLES: u32 = 300; // about 6000ns
+//const FRAME_DELAY_CYCLES: u32 = 1_000_000; // about 20ms, but doesn't count the time for the other operations
+
+pub struct NeopixelLights<T: OutputPin> {
+    out: T
+}
+
+impl<T: OutputPin> NeopixelLights<T> {
+    #[inline]
+    fn write(&mut self, bit: bool) {
+        self.out.set_high();
+        delay(if bit { ONE_HIGH_CYCLES } else { ZERO_HIGH_CYCLES });
+        self.out.set_low();
+        delay(DATA_LOW_CYCLES);
+    }
+
+    #[inline]
+    fn byte(&mut self, byte: u8) {
+        self.write(byte & 0x80 != 0);
+        self.write(byte & 0x40 != 0);
+        self.write(byte & 0x20 != 0);
+        self.write(byte & 0x10 != 0);
+        self.write(byte & 0x08 != 0);
+        self.write(byte & 0x04 != 0);
+        self.write(byte & 0x02 != 0);
+        self.write(byte & 0x01 != 0);
+    }
+}
+
+impl<T: OutputPin> Lights for NeopixelLights<T> {
+    type Pixel = CorrectedRgb;
+
+    #[inline]
+    fn render(&mut self, rgb: &CorrectedRgb) {
+        // GRB pixel order
+        self.byte(rgb.1);
+        self.byte(rgb.0);
+        self.byte(rgb.2);
+    }
+    fn latch(&mut self) {
+        delay(LATCH_CYCLES);
+    }
+}