Added PIO pwm examples for rp

Two additionally `rp` examples, `pio_pwm.rs`, which is a baremetal example of how to do pwm with pio, and `pio_servo.rs`, which is a more extended example of pwm and pio with servos.

examples/rp/src/bin/pio_pwm.rs

@@ -0,0 +1,118 @@
+//! This example shows how to create a pwm using the PIO module in the RP2040 chip.
+
+#![no_std]
+#![no_main]
+use core::time::Duration;
+
+use embassy_executor::Spawner;
+use embassy_rp::gpio::Level;
+use embassy_rp::peripherals::PIO0;
+use embassy_rp::pio::{Common, Config, Direction, Instance, InterruptHandler, Pio, PioPin, StateMachine};
+use embassy_rp::{bind_interrupts, clocks};
+use embassy_time::Timer;
+use pio::InstructionOperands;
+use {defmt_rtt as _, panic_probe as _};
+
+const REFRESH_INTERVAL: u64 = 20000;
+
+bind_interrupts!(struct Irqs {
+    PIO0_IRQ_0 => InterruptHandler<PIO0>;
+});
+
+pub fn to_pio_cycles(duration: Duration) -> u32 {
+    (clocks::clk_sys_freq() / 1_000_000) / 3 * duration.as_micros() as u32 // parentheses are required to prevent overflow
+}
+
+pub struct PwmPio<'d, T: Instance, const SM: usize> {
+    sm: StateMachine<'d, T, SM>,
+}
+
+impl<'d, T: Instance, const SM: usize> PwmPio<'d, T, SM> {
+    pub fn attach(pio: &mut Common<'d, T>, mut sm: StateMachine<'d, T, SM>, pin: impl PioPin) -> Self {
+        let prg = pio_proc::pio_asm!(
+            ".side_set 1 opt"
+                "pull noblock    side 0"
+                "mov x, osr"
+                "mov y, isr"
+            "countloop:"
+                "jmp x!=y noset"
+                "jmp skip        side 1"
+            "noset:"
+                "nop"
+            "skip:"
+                "jmp y-- countloop"
+        );
+
+        pio.load_program(&prg.program);
+        let pin = pio.make_pio_pin(pin);
+        sm.set_pins(Level::High, &[&pin]);
+        sm.set_pin_dirs(Direction::Out, &[&pin]);
+
+        let mut cfg = Config::default();
+        cfg.use_program(&pio.load_program(&prg.program), &[&pin]);
+
+        sm.set_config(&cfg);
+
+        Self { sm }
+    }
+
+    pub fn start(&mut self) {
+        self.sm.set_enable(true);
+    }
+
+    pub fn stop(&mut self) {
+        self.sm.set_enable(false);
+    }
+
+    pub fn set_period(&mut self, duration: Duration) {
+        let is_enabled = self.sm.is_enabled();
+        while !self.sm.tx().empty() {} // Make sure that the queue is empty
+        self.sm.set_enable(false);
+        self.sm.tx().push(to_pio_cycles(duration));
+        unsafe {
+            self.sm.exec_instr(
+                InstructionOperands::PULL {
+                    if_empty: false,
+                    block: false,
+                }
+                .encode(),
+            );
+            self.sm.exec_instr(
+                InstructionOperands::OUT {
+                    destination: ::pio::OutDestination::ISR,
+                    bit_count: 32,
+                }
+                .encode(),
+            );
+        };
+        if is_enabled {
+            self.sm.set_enable(true) // Enable if previously enabled
+        }
+    }
+
+    pub fn set_level(&mut self, level: u32) {
+        self.sm.tx().push(level);
+    }
+
+    pub fn write(&mut self, duration: Duration) {
+        self.set_level(to_pio_cycles(duration));
+    }
+}
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_rp::init(Default::default());
+    let Pio { mut common, sm0, .. } = Pio::new(p.PIO0, Irqs);
+
+    // Note that PIN_25 is the led pin on the Pico
+    let mut pwm_pio = PwmPio::attach(&mut common, sm0, p.PIN_25);
+    pwm_pio.set_period(Duration::from_micros(REFRESH_INTERVAL));
+    pwm_pio.start();
+
+    let mut duration = 0;
+    loop {
+        duration = (duration + 1) % 1000;
+        pwm_pio.write(Duration::from_micros(duration));
+        Timer::after_millis(1).await;
+    }
+}

examples/rp/src/bin/pio_servo.rs

@@ -0,0 +1,208 @@
+//! This example shows how to create a pwm using the PIO module in the RP2040 chip.
+
+#![no_std]
+#![no_main]
+use core::time::Duration;
+
+use embassy_executor::Spawner;
+use embassy_rp::gpio::Level;
+use embassy_rp::peripherals::PIO0;
+use embassy_rp::pio::{Common, Config, Direction, Instance, InterruptHandler, Pio, PioPin, StateMachine};
+use embassy_rp::{bind_interrupts, clocks};
+use embassy_time::Timer;
+use pio::InstructionOperands;
+use {defmt_rtt as _, panic_probe as _};
+
+const DEFAULT_MIN_PULSE_WIDTH: u64 = 1000; // uncalibrated default, the shortest duty cycle sent to a servo
+const DEFAULT_MAX_PULSE_WIDTH: u64 = 2000; // uncalibrated default, the longest duty cycle sent to a servo
+const DEFAULT_MAX_DEGREE_ROTATION: u64 = 160; // 160 degrees is typical
+const REFRESH_INTERVAL: u64 = 20000; // The period of each cycle
+
+bind_interrupts!(struct Irqs {
+    PIO0_IRQ_0 => InterruptHandler<PIO0>;
+});
+
+pub fn to_pio_cycles(duration: Duration) -> u32 {
+    (clocks::clk_sys_freq() / 1_000_000) / 3 * duration.as_micros() as u32 // parentheses are required to prevent overflow
+}
+
+pub struct PwmPio<'d, T: Instance, const SM: usize> {
+    sm: StateMachine<'d, T, SM>,
+}
+
+impl<'d, T: Instance, const SM: usize> PwmPio<'d, T, SM> {
+    pub fn attach(pio: &mut Common<'d, T>, mut sm: StateMachine<'d, T, SM>, pin: impl PioPin) -> Self {
+        let prg = pio_proc::pio_asm!(
+            ".side_set 1 opt"
+                "pull noblock    side 0"
+                "mov x, osr"
+                "mov y, isr"
+            "countloop:"
+                "jmp x!=y noset"
+                "jmp skip        side 1"
+            "noset:"
+                "nop"
+            "skip:"
+                "jmp y-- countloop"
+        );
+
+        pio.load_program(&prg.program);
+        let pin = pio.make_pio_pin(pin);
+        sm.set_pins(Level::High, &[&pin]);
+        sm.set_pin_dirs(Direction::Out, &[&pin]);
+
+        let mut cfg = Config::default();
+        cfg.use_program(&pio.load_program(&prg.program), &[&pin]);
+
+        sm.set_config(&cfg);
+
+        Self { sm }
+    }
+
+    pub fn start(&mut self) {
+        self.sm.set_enable(true);
+    }
+
+    pub fn stop(&mut self) {
+        self.sm.set_enable(false);
+    }
+
+    pub fn set_period(&mut self, duration: Duration) {
+        let is_enabled = self.sm.is_enabled();
+        while !self.sm.tx().empty() {} // Make sure that the queue is empty
+        self.sm.set_enable(false);
+        self.sm.tx().push(to_pio_cycles(duration));
+        unsafe {
+            self.sm.exec_instr(
+                InstructionOperands::PULL {
+                    if_empty: false,
+                    block: false,
+                }
+                .encode(),
+            );
+            self.sm.exec_instr(
+                InstructionOperands::OUT {
+                    destination: ::pio::OutDestination::ISR,
+                    bit_count: 32,
+                }
+                .encode(),
+            );
+        };
+        if is_enabled {
+            self.sm.set_enable(true) // Enable if previously enabled
+        }
+    }
+
+    pub fn set_level(&mut self, level: u32) {
+        self.sm.tx().push(level);
+    }
+
+    pub fn write(&mut self, duration: Duration) {
+        self.set_level(to_pio_cycles(duration));
+    }
+}
+
+pub struct ServoBuilder<'d, T: Instance, const SM: usize> {
+    pwm: PwmPio<'d, T, SM>,
+    period: Duration,
+    min_pulse_width: Duration,
+    max_pulse_width: Duration,
+    max_degree_rotation: u64,
+}
+
+impl<'d, T: Instance, const SM: usize> ServoBuilder<'d, T, SM> {
+    pub fn new(pwm: PwmPio<'d, T, SM>) -> Self {
+        Self {
+            pwm,
+            period: Duration::from_micros(REFRESH_INTERVAL),
+            min_pulse_width: Duration::from_micros(DEFAULT_MIN_PULSE_WIDTH),
+            max_pulse_width: Duration::from_micros(DEFAULT_MAX_PULSE_WIDTH),
+            max_degree_rotation: DEFAULT_MAX_DEGREE_ROTATION,
+        }
+    }
+
+    pub fn set_period(mut self, duration: Duration) -> Self {
+        self.period = duration;
+        self
+    }
+
+    pub fn set_min_pulse_width(mut self, duration: Duration) -> Self {
+        self.min_pulse_width = duration;
+        self
+    }
+
+    pub fn set_max_pulse_width(mut self, duration: Duration) -> Self {
+        self.max_pulse_width = duration;
+        self
+    }
+
+    pub fn set_max_degree_rotation(mut self, degree: u64) -> Self {
+        self.max_degree_rotation = degree;
+        self
+    }
+
+    pub fn build(mut self) -> Servo<'d, T, SM> {
+        self.pwm.set_period(self.period);
+        Servo {
+            pwm: self.pwm,
+            min_pulse_width: self.min_pulse_width,
+            max_pulse_width: self.max_pulse_width,
+            max_degree_rotation: self.max_degree_rotation,
+        }
+    }
+}
+
+pub struct Servo<'d, T: Instance, const SM: usize> {
+    pwm: PwmPio<'d, T, SM>,
+    min_pulse_width: Duration,
+    max_pulse_width: Duration,
+    max_degree_rotation: u64,
+}
+
+impl<'d, T: Instance, const SM: usize> Servo<'d, T, SM> {
+    pub fn start(&mut self) {
+        self.pwm.start();
+    }
+
+    pub fn stop(&mut self) {
+        self.pwm.stop();
+    }
+
+    pub fn write_time(&mut self, duration: Duration) {
+        self.pwm.write(duration);
+    }
+
+    pub fn rotate(&mut self, degree: u64) {
+        let degree_per_nano_second = (self.max_pulse_width.as_nanos() as u64 - self.min_pulse_width.as_nanos() as u64)
+            / self.max_degree_rotation;
+        let mut duration =
+            Duration::from_nanos(degree * degree_per_nano_second + self.min_pulse_width.as_nanos() as u64);
+        if self.max_pulse_width < duration {
+            duration = self.max_pulse_width;
+        }
+
+        self.pwm.write(duration);
+    }
+}
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_rp::init(Default::default());
+    let Pio { mut common, sm0, .. } = Pio::new(p.PIO0, Irqs);
+
+    let pwm_pio = PwmPio::attach(&mut common, sm0, p.PIN_1);
+    let mut servo = ServoBuilder::new(pwm_pio)
+        .set_max_degree_rotation(120) // Example of adjusting values for MG996R servo
+        .set_min_pulse_width(Duration::from_micros(350)) // This value was detemined by a rough experiment.
+        .set_max_pulse_width(Duration::from_micros(2600)) // Along with this value.
+        .build();
+
+    servo.start();
+
+    let mut degree = 0;
+    loop {
+        degree = (degree + 1) % 120;
+        servo.rotate(degree);
+        Timer::after_millis(50).await;
+    }
+}