Add extensive explanation of the code.

halloween-leds/src/main.rs

@@ -1,14 +1,21 @@
 #![no_main]
 #![no_std]
 
-use embedded_hal::delay::DelayNs;
-use embedded_hal::spi::SpiBus;
+/// This application demonstrates using a Raspberry Pi Pico to control an individual SK9822 module.
+/// Keep in mind that the Pico, though it accepts 5V for power, it runs on 3.3V logic. The GPIO
+/// pins will emit only 3.3 volts, and the SK9822 needs 5V logic. So, make sure that the GPIO pins
+/// run through a transistor or a logic level lhifter to go from 3.3V logic to 5V logic.
+use embedded_hal::{delay::DelayNs, spi::SpiBus};
 use panic_halt as _;
 use rp_pico::{
     entry,
     hal::{
         clocks::init_clocks_and_plls,
         fugit::RateExtU32,
+        gpio::{
+            bank0::{Gpio10, Gpio11},
+            FunctionSpi, Pin, PullDown,
+        },
         spi::Spi,
         Clock, Sio, Timer, Watchdog,
     },
@@ -21,15 +28,28 @@ const XOSC_CRYSTAL_FREQ: u32 = 12_000_000; // MHz, https://forums.raspberrypi.co
 
 #[entry]
 unsafe fn main() -> ! {
+    // rp_pico::pac::Peripherals is a reference to physical hardware defined on the Pico.
     let mut peripherals = pac::Peripherals::take().unwrap();
+
+    // SIO inidcates "Single Cycle IO". I don't know what this means, but it could mean that this
+    // is a class of IO operations that can be run in a single clock cycle, such as switching a
+    // GPIO pin on or off.
     let sio = Sio::new(peripherals.SIO);
+
+    // Many of the following systems require a watchdog. I do not know what this does, either, but
+    // it may be some failsafe software that will reset operations if the watchdog detects a lack
+    // of activity.
     let mut watchdog = Watchdog::new(peripherals.WATCHDOG);
+
+    // Here we grab the GPIO pins in bank 0.
     let pins = Pins::new(
         peripherals.IO_BANK0,
         peripherals.PADS_BANK0,
         sio.gpio_bank0,
         &mut peripherals.RESETS,
     );
+
+    // Initialize an abstraction of the clock system with a batch of standard hardware clocks.
     let clocks = init_clocks_and_plls(
         XOSC_CRYSTAL_FREQ,
         peripherals.XOSC,
@@ -42,15 +62,23 @@ unsafe fn main() -> ! {
     .ok()
     .unwrap();
 
+    // An abstraction for a timer which we can use to delay the code.
     let mut timer = Timer::new(peripherals.TIMER, &mut peripherals.RESETS, &clocks);
 
-    let spi_clk = pins.gpio10.into_function();
-    let spi_sdo = pins.gpio11.into_function();
-    let spi = Spi::<_, _, _, 8>::new(peripherals.SPI1, (spi_sdo, spi_clk));
-    let mut spi = spi.init(
+    // Grab the clock and data pins for SPI1. For Clock pins and for Data pins, there are only two
+    // pins each on the Pico which can function for SPI1.
+    let spi_clk: Pin<Gpio10, FunctionSpi, PullDown> = pins.gpio10.into_function();
+    let spi_sdo: Pin<Gpio11, FunctionSpi, PullDown> = pins.gpio11.into_function();
+
+    // Now, create the SPI function abstraction for SPI1 with spi_clk and spi_sdo.
+    let mut spi = Spi::<_, _, _, 8>::new(peripherals.SPI1, (spi_sdo, spi_clk)).init(
         &mut peripherals.RESETS,
+        // The SPI system uses the peripheral clock
         clocks.peripheral_clock.freq(),
+        // Transmit data at a rate of 1Mbit.
         1_u32.MHz(),
+        // Run with SPI Mode 1. This means that the clock line should start high and that data will
+        // be sampled starting at the first falling edge.
         embedded_hal::spi::MODE_1,
     );
 
@@ -59,13 +87,27 @@ unsafe fn main() -> ! {
     //             4 for the end frame
     //             = 20 bytes
     let mut lights: [u8; 12] = [0; 12];
+    // We just skip the first four bytes, because the start frame is four bytes of 0.
+
+    // Set the first byte of the one and only lamp. The first byte follows the pattern of three 1
+    // bits followed by five additional bits that indicate an overall brightness level of the
+    // pixel. The datasheet for the SK9822 doesn't specify the exact effect, but it does mean that
+    // the higher this number is, the brighter 255 means for an given LED in the array. 1 is the
+    // lowest brightness that emits light, and 31 is the highest supported brightness.
+    lights[4] = 0xe0 + 1;
+    // Set the Blue light of the dotstar to 255, assuming the dotstar frame format is RBG. Note
+    // that the standard SK9822 datasheed indicates that the format is BGR. Your mileage may vary.
+    lights[6] = 255;
+
+    // The end frame is four bytes of 255.
     lights[8] = 0xff;
     lights[9] = 0xff;
     lights[10] = 0xff;
     lights[11] = 0xff;
 
-    lights[4] = 0xe0 + 1;
 
+    // The rest of this is just a stock pulsating animation which is slightly brightening and
+    // dimming the *blue* LED (on my set of dotstars).
     let mut brightness = 1;
     let mut step = 1;
     loop {
@@ -75,8 +117,6 @@ unsafe fn main() -> ! {
             step = 1;
         };
         lights[5] = brightness as u8;
-        lights[6] = 255;
-        // lights[7] = brightness as u8;
         brightness = brightness + step;
 
         let _ = spi.write(lights.as_slice());