Add extensive explanation of the code.

halloween-leds/src/main.rs

@@ -1,39 +1,55 @@
 #![no_main]
 #![no_std]
 
-use embedded_hal::{delay::DelayNs, digital::OutputPin};
-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::hal::gpio::bank0::Gpio0;
 use rp_pico::{
     entry,
     hal::{
         clocks::init_clocks_and_plls,
         fugit::RateExtU32,
         gpio::{
-            bank0::{Gpio2, Gpio4},
-            FunctionSio, Pin, PullDown, SioOutput,
+            bank0::{Gpio10, Gpio11},
+            FunctionSpi, Pin, PullDown,
         },
-        spi::{Enabled, Spi, SpiDevice, ValidSpiPinout},
-        uart::{DataBits, StopBits, UartConfig, UartPeripheral},
+        spi::Spi,
         Clock, Sio, Timer, Watchdog,
     },
     pac, Pins,
 };
 
+const FPS: u32 = 60;
+const MS_PER_FRAME: u32 = 1000 / FPS;
 const XOSC_CRYSTAL_FREQ: u32 = 12_000_000; // MHz, https://forums.raspberrypi.com/viewtopic.php?t=356764
 
 #[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,
@@ -46,58 +62,64 @@ unsafe fn main() -> ! {
     .ok()
     .unwrap();
 
-    // let mut power_light: Pin<Gpio0, FunctionSio<SioOutput>, PullDown> = pins.gpio0.into_function();
-    // power_light.set_high();
+    // 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,
     );
 
-    let mut lights: [u8; 126] = [0; 126];
-    lights[124] = 0xff;
-    lights[125] = 0xff;
-    for i in 0..30 {
-        lights[(i + 1) * 4 + 0] = 0xe0 + 1;
-        lights[(i + 1) * 4 + 1] = 255;
-    }
+    // byte count: 4 for the start frame
+    //             1 * 4 for three lights with 4 bytes per light
+    //             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;
+
+
+    // 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 {
-        if brightness == 255 && step == 1 {
+        if brightness == 64 && step == 1 {
             step = -1;
         } else if brightness == 1 && step == -1 {
             step = 1;
         };
-        for i in 0..30 {
-            lights[(i + 1) * 4 + 3] = brightness as u8;
-        }
+        lights[5] = brightness as u8;
         brightness = brightness + step;
-        
-        spi.write(lights.as_slice());
-        timer.delay_ms(10);
+
+        let _ = spi.write(lights.as_slice());
+        timer.delay_ms(MS_PER_FRAME);
     }
-
-    /*
-    let pins = (pins.gpio0.into_function(), pins.gpio1.into_function());
-
-    let uart = UartPeripheral::new(peripherals.UART0, pins, &mut peripherals.RESETS)
-        .enable(
-            UartConfig::new(9600_u32.Hz(), DataBits::Eight, None, StopBits::One),
-            clocks.peripheral_clock.freq(),
-        )
-        .unwrap();
-
-    loop {
-        uart.write_full_blocking(b"Hello World!\r\n");
-        timer.delay_ms(1000);
-    }
-    */
 }