Polish PWM blink example.

rp2040-hal/examples/pwm_blink.rs

@@ -1,43 +1,124 @@
+//! # PWM Blink Example
+//!
+//! If you have an LED connected to pin 25, it will fade the LED using the PWM
+//! peripheral.
+//!
+//! It may need to be adapted to your particular board layout and/or pin assignment.
+//!
+//! See the `Cargo.toml` file for Copyright and licence details.
+
 #![no_std]
 #![no_main]
 
+// The macro for our start-up function
 use cortex_m_rt::entry;
-use embedded_hal::PwmPin;
-use panic_halt as _;
-use rp2040_hal::{gpio::Pins, pwm::*, sio::Sio};
 
+// Ensure we halt the program on panic (if we don't mention this crate it won't
+// be linked)
+use panic_halt as _;
+
+// Alias for our HAL crate
+use rp2040_hal as hal;
+
+// Traits we need
+use embedded_hal::PwmPin;
+use embedded_time::rate::*;
+use rp2040_hal::clocks::Clock;
+
+// A shorter alias for the Peripheral Access Crate, which provides low-level
+// register access
+use hal::pac;
+
+//// The linker will place this boot block at the start of our program image. We
+//// need this to help the ROM bootloader get our code up and running.
 #[link_section = ".boot2"]
 #[used]
 pub static BOOT2: [u8; 256] = rp2040_boot2::BOOT_LOADER;
 
+/// The minimum PWM value (i.e. LED brightness) we want
+const LOW: u16 = 0;
+
+/// The maximum PWM value (i.e. LED brightness) we want
+const HIGH: u16 = 25000;
+
+/// External high-speed crystal on the Raspberry Pi Pico board is 12 MHz. Adjust
+/// if your board has a different frequency
+const XTAL_FREQ_HZ: u32 = 12_000_000u32;
+
+/// 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 fades the LED in an
+/// infinite loop.
 #[entry]
 fn main() -> ! {
-    let mut pac = rp2040_pac::Peripherals::take().unwrap();
+    // Grab our singleton objects
+    let mut pac = pac::Peripherals::take().unwrap();
+    let core = pac::CorePeripherals::take().unwrap();
 
-    let sio = Sio::new(pac.SIO);
-    let pins = Pins::new(
+    // Set up the watchdog driver - needed by the clock setup code
+    let mut watchdog = hal::watchdog::Watchdog::new(pac.WATCHDOG);
+
+    // Configure the clocks
+    //
+    // The default is to generate a 125 MHz system clock
+    let clocks = hal::clocks::init_clocks_and_plls(
+        XTAL_FREQ_HZ,
+        pac.XOSC,
+        pac.CLOCKS,
+        pac.PLL_SYS,
+        pac.PLL_USB,
+        &mut pac.RESETS,
+        &mut watchdog,
+    )
+    .ok()
+    .unwrap();
+
+    // The single-cycle I/O block controls our GPIO pins
+    let sio = hal::sio::Sio::new(pac.SIO);
+
+    // Set the pins up according to their function on this particular board
+    let pins = hal::gpio::Pins::new(
         pac.IO_BANK0,
         pac.PADS_BANK0,
         sio.gpio_bank0,
         &mut pac.RESETS,
     );
 
+    // The delay object lets us wait for specified amounts of time (in
+    // milliseconds)
+    let mut delay = cortex_m::delay::Delay::new(core.SYST, clocks.system_clock.freq().integer());
+
     // Init PWMs
-    let pwm_slices = Slices::new(pac.PWM, &mut pac.RESETS);
+    let mut pwm_slices = hal::pwm::Slices::new(pac.PWM, &mut pac.RESETS);
 
     // Configure PWM4
-    let mut pwm = pwm_slices.pwm4;
+    let pwm = &mut pwm_slices.pwm4;
     pwm.set_ph_correct();
     pwm.enable();
 
-    // Use B channel (which outputs to GPIO 25)
-    let mut channel = pwm.channel_b;
+    // Output channel B on PWM4 to GPIO 25
+    let channel = &mut pwm.channel_b;
     channel.output_to(pins.gpio25);
+
+    // Infinite loop, fading LED up and down
     loop {
-        channel.set_duty(15000);
-        // TODO: Replace with proper delays once we have clocks working
-        cortex_m::asm::delay(5_000_000);
-        channel.set_duty(30000);
-        cortex_m::asm::delay(5_000_000);
+        // Ramp brightness up
+        for i in (LOW..=HIGH).skip(100) {
+            delay.delay_us(8);
+            channel.set_duty(i);
+        }
+
+        // Ramp brightness down
+        for i in (LOW..=HIGH).rev().skip(100) {
+            delay.delay_us(8);
+            channel.set_duty(i);
+        }
+
+        delay.delay_ms(500);
     }
 }
+
+// End of file