Add Pico PWM micro servo example (#346)

* Add micro servo with pwm working example

Signed-off-by: lucazulian <lucagiuggia@gmail.com>

* Add duty value suggestion

Signed-off-by: lucazulian <lucagiuggia@gmail.com>

* Fix code formatting

* Use CountDown instead of Delay

boards/rp-pico/README.md

@@ -76,6 +76,10 @@ Another LED blinking example, but using a Timer in count-down mode.
 
 Puts out an analog 'triangle wave' on GPIO 25, using the PWM hardware.
 
+### [pico_pwm_servo](./examples/pico_pwm_servo.rs)
+
+Demonstrates handling a micro servo, using the PWM hardware.
+
 ### [pico_usb_serial](./examples/pico_usb_serial.rs)
 
 Creates a USB Serial device on a Pico board.

boards/rp-pico/examples/pico_pwm_servo.rs

@@ -0,0 +1,119 @@
+//! # Pico PWM Micro Servo Example
+//!
+//! Moves the micro servo on a Pico board using the PWM peripheral.
+//!
+//! This will move in different positions the motor attached to GP1.
+//!
+//! See the `Cargo.toml` file for Copyright and license details.
+
+#![no_std]
+#![no_main]
+
+// The macro for our start-up function
+use cortex_m_rt::entry;
+
+use cortex_m::prelude::*;
+
+// GPIO traits
+use embedded_hal::PwmPin;
+
+// Traits for converting integers to amounts of time
+use embedded_time::duration::Extensions;
+
+// Ensure we halt the program on panic (if we don't mention this crate it won't
+// be linked)
+use panic_halt as _;
+
+// A shorter alias for the Peripheral Access Crate, which provides low-level
+// register access
+use rp_pico::hal::pac;
+
+// A shorter alias for the Hardware Abstraction Layer, which provides
+// higher-level drivers.
+use rp_pico::hal;
+
+/// 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() -> ! {
+    // Grab our singleton objects
+    let mut pac = pac::Peripherals::take().unwrap();
+
+    // Set up the watchdog driver - needed by the clock setup code
+    let mut watchdog = hal::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(
+        rp_pico::XOSC_CRYSTAL_FREQ,
+        pac.XOSC,
+        pac.CLOCKS,
+        pac.PLL_SYS,
+        pac.PLL_USB,
+        &mut pac.RESETS,
+        &mut watchdog,
+    )
+    .ok()
+    .unwrap();
+
+    // Configure the Timer peripheral in count-down mode
+    let timer = hal::Timer::new(pac.TIMER, &mut pac.RESETS);
+    let mut count_down = timer.count_down();
+
+    // The single-cycle I/O block controls our GPIO pins
+    let sio = hal::Sio::new(pac.SIO);
+
+    // Set the pins up according to their function on this particular board
+    let pins = rp_pico::Pins::new(
+        pac.IO_BANK0,
+        pac.PADS_BANK0,
+        sio.gpio_bank0,
+        &mut pac.RESETS,
+    );
+
+    // Init PWMs
+    let mut pwm_slices = hal::pwm::Slices::new(pac.PWM, &mut pac.RESETS);
+
+    // Configure PWM0
+    let pwm = &mut pwm_slices.pwm0;
+    pwm.set_ph_correct();
+    pwm.set_div_int(20u8); // 50 hz
+    pwm.enable();
+
+    // Output channel B on PWM0 to the GPIO1 pin
+    let channel = &mut pwm.channel_b;
+    channel.output_to(pins.gpio1);
+
+    // Infinite loop, moving micro servo from one position to another.
+    // You may need to adjust the pulse width since several servos from
+    // different manufacturers respond differently.
+    loop {
+        // move to 0°
+        channel.set_duty(2500);
+        count_down.start(400.milliseconds());
+        let _ = nb::block!(count_down.wait());
+
+        // 0° to 90°
+        channel.set_duty(3930);
+        count_down.start(400.milliseconds());
+        let _ = nb::block!(count_down.wait());
+
+        // 90° to 180°
+        channel.set_duty(7860);
+        count_down.start(400.milliseconds());
+        let _ = nb::block!(count_down.wait());
+
+        // 180° to 90°
+        channel.set_duty(3930);
+        count_down.start(400.milliseconds());
+        let _ = nb::block!(count_down.wait());
+    }
+}
+
+// End of file