Merge #591

591: PWM WS2812B example and flexible sequence config r=Dirbaio a=huntc

I've permitted the PWM sequences to be mutated on stopping the PWM by associating them with a new  `SingleSequencer` structure. This is so that we can perform effects on the LEDs (and other use-cases, I'm sure!). The example has been updated to illustrate the use of this by flashing a WS2812B LED.

There's also a `Sequencer` structure for more sophisticated PWM interactions, along with a `pwm_double_sequence`  example to illustrate.

These changes should make it possible to attain all of the nRF PWM functionality available.

Co-authored-by: huntc <[email protected]>

5 files changed, 368 insertions, 129 deletions

diff --git a/embassy-nrf/src/pwm.rs b/embassy-nrf/src/pwm.rs
index a77cd6332..01b1f48d9 100644
--- a/embassy-nrf/src/pwm.rs
+++ b/embassy-nrf/src/pwm.rs
@@ -45,6 +45,8 @@ pub enum Error {
     DMABufferNotInDataMemory,
 }
 
+const MAX_SEQUENCE_LEN: usize = 32767;
+
 impl<'d, T: Instance> SequencePwm<'d, T> {
     /// Creates the interface to a `SequencePwm`.
     ///
@@ -62,7 +64,7 @@ impl<'d, T: Instance> SequencePwm<'d, T> {
         ch1: impl Unborrow<Target = impl GpioOptionalPin> + 'd,
         ch2: impl Unborrow<Target = impl GpioOptionalPin> + 'd,
         ch3: impl Unborrow<Target = impl GpioOptionalPin> + 'd,
-        config: SequenceConfig,
+        config: Config,
     ) -> Result<Self, Error> {
         unborrow!(ch0, ch1, ch2, ch3);
 
@@ -117,16 +119,6 @@ impl<'d, T: Instance> SequencePwm<'d, T> {
         r.countertop
             .write(|w| unsafe { w.countertop().bits(config.max_duty) });
 
-        r.seq0.refresh.write(|w| unsafe { w.bits(config.refresh) });
-        r.seq0
-            .enddelay
-            .write(|w| unsafe { w.bits(config.end_delay) });
-
-        r.seq1.refresh.write(|w| unsafe { w.bits(config.refresh) });
-        r.seq1
-            .enddelay
-            .write(|w| unsafe { w.bits(config.end_delay) });
-
         Ok(Self {
             phantom: PhantomData,
             ch0: ch0.degrade_optional(),
@@ -136,80 +128,6 @@ impl<'d, T: Instance> SequencePwm<'d, T> {
         })
     }
 
-    /// Start or restart playback
-    #[inline(always)]
-    pub fn start(&mut self, sequence: &'d [u16], times: SequenceMode) -> Result<(), Error> {
-        slice_in_ram_or(sequence, Error::DMABufferNotInDataMemory)?;
-
-        if sequence.len() > 32767 {
-            return Err(Error::SequenceTooLong);
-        }
-
-        if let SequenceMode::Times(0) = times {
-            return Err(Error::SequenceTimesAtLeastOne);
-        }
-
-        self.stop();
-
-        let r = T::regs();
-
-        r.seq0
-            .ptr
-            .write(|w| unsafe { w.bits(sequence.as_ptr() as u32) });
-        r.seq0
-            .cnt
-            .write(|w| unsafe { w.bits(sequence.len() as u32) });
-
-        r.seq1
-            .ptr
-            .write(|w| unsafe { w.bits(sequence.as_ptr() as u32) });
-        r.seq1
-            .cnt
-            .write(|w| unsafe { w.bits(sequence.len() as u32) });
-
-        r.enable.write(|w| w.enable().enabled());
-
-        // defensive before seqstart
-        compiler_fence(Ordering::SeqCst);
-
-        match times {
-            // just the one time, no loop count
-            SequenceMode::Times(1) => {
-                r.loop_.write(|w| w.cnt().disabled());
-                // tasks_seqstart() doesn't exist in all svds so write its bit instead
-                r.tasks_seqstart[0].write(|w| unsafe { w.bits(0x01) });
-            }
-            // loop count is how many times to play BOTH sequences
-            // 2 total  (1 x 2)
-            // 3 total, (2 x 2) - 1
-            SequenceMode::Times(n) => {
-                let odd = n & 1 == 1;
-                let times = if odd { (n / 2) + 1 } else { n / 2 };
-
-                r.loop_.write(|w| unsafe { w.cnt().bits(times) });
-
-                // we can subtract 1 by starting at seq1 instead of seq0
-                if odd {
-                    // tasks_seqstart() doesn't exist in all svds so write its bit instead
-                    r.tasks_seqstart[1].write(|w| unsafe { w.bits(0x01) });
-                } else {
-                    // tasks_seqstart() doesn't exist in all svds so write its bit instead
-                    r.tasks_seqstart[0].write(|w| unsafe { w.bits(0x01) });
-                }
-            }
-            // to play infinitely, repeat the sequence one time, then have loops done self trigger seq0 again
-            SequenceMode::Infinite => {
-                r.loop_.write(|w| unsafe { w.cnt().bits(0x1) });
-                r.shorts.write(|w| w.loopsdone_seqstart0().enabled());
-
-                // tasks_seqstart() doesn't exist in all svds so write its bit instead
-                r.tasks_seqstart[0].write(|w| unsafe { w.bits(0x01) });
-            }
-        }
-
-        Ok(())
-    }
-
     /// Returns reference to `Stopped` event endpoint for PPI.
     #[inline(always)]
     pub fn event_stopped(&self) -> Event {
@@ -309,30 +227,12 @@ impl<'d, T: Instance> SequencePwm<'d, T> {
 
         Task::from_reg(&r.tasks_stop)
     }
-
-    /// Stop playback. Disables the peripheral. Does NOT clear the last duty
-    /// cycle from the pin.
-    #[inline(always)]
-    pub fn stop(&self) {
-        let r = T::regs();
-
-        r.shorts.reset();
-
-        compiler_fence(Ordering::SeqCst);
-
-        // tasks_stop() doesn't exist in all svds so write its bit instead
-        r.tasks_stop.write(|w| unsafe { w.bits(0x01) });
-
-        r.enable.write(|w| w.enable().disabled());
-    }
 }
 
 impl<'a, T: Instance> Drop for SequencePwm<'a, T> {
     fn drop(&mut self) {
         let r = T::regs();
 
-        self.stop();
-
         if let Some(pin) = &self.ch0 {
             pin.set_low();
             pin.conf().reset();
@@ -356,9 +256,9 @@ impl<'a, T: Instance> Drop for SequencePwm<'a, T> {
     }
 }
 
-/// Configure an infinite looping sequence for `SequencePwm`
+/// Configuration for the PWM as a whole.
 #[non_exhaustive]
-pub struct SequenceConfig {
+pub struct Config {
     /// Selects up mode or up-and-down mode for the counter
     pub counter_mode: CounterMode,
     /// Top value to be compared against buffer values
@@ -367,6 +267,23 @@ pub struct SequenceConfig {
     pub prescaler: Prescaler,
     /// How a sequence is read from RAM and is spread to the compare register
     pub sequence_load: SequenceLoad,
+}
+
+impl Default for Config {
+    fn default() -> Config {
+        Config {
+            counter_mode: CounterMode::Up,
+            max_duty: 1000,
+            prescaler: Prescaler::Div16,
+            sequence_load: SequenceLoad::Common,
+        }
+    }
+}
+
+/// Configuration per sequence
+#[non_exhaustive]
+#[derive(Clone)]
+pub struct SequenceConfig {
     /// Number of PWM periods to delay between each sequence sample
     pub refresh: u32,
     /// Number of PWM periods after the sequence ends before starting the next sequence
@@ -376,25 +293,219 @@ pub struct SequenceConfig {
 impl Default for SequenceConfig {
     fn default() -> SequenceConfig {
         SequenceConfig {
-            counter_mode: CounterMode::Up,
-            max_duty: 1000,
-            prescaler: Prescaler::Div16,
-            sequence_load: SequenceLoad::Common,
             refresh: 0,
             end_delay: 0,
         }
     }
 }
 
-/// How many times to run the sequence
+/// A composition of a sequence buffer and its configuration.
+#[non_exhaustive]
+pub struct Sequence<'s> {
+    /// The words comprising the sequence. Must not exceed 32767 words.
+    pub words: &'s [u16],
+    /// Configuration associated with the sequence.
+    pub config: SequenceConfig,
+}
+
+impl<'s> Sequence<'s> {
+    pub fn new(words: &'s [u16], config: SequenceConfig) -> Self {
+        Self { words, config }
+    }
+}
+
+/// A single sequence that can be started and stopped.
+/// Takes at one sequence along with its configuration.
+#[non_exhaustive]
+pub struct SingleSequencer<'d, 's, T: Instance> {
+    pub sequencer: Sequencer<'d, 's, T>,
+}
+
+impl<'d, 's, T: Instance> SingleSequencer<'d, 's, T> {
+    /// Create a new sequencer
+    pub fn new(pwm: &'s mut SequencePwm<'d, T>, words: &'s [u16], config: SequenceConfig) -> Self {
+        Self {
+            sequencer: Sequencer::new(pwm, Sequence::new(words, config), None),
+        }
+    }
+
+    /// Start or restart playback.
+    #[inline(always)]
+    pub fn start(&self, times: SingleSequenceMode) -> Result<(), Error> {
+        let (start_seq, times) = match times {
+            SingleSequenceMode::Times(n) if n == 1 => (StartSequence::One, SequenceMode::Loop(1)),
+            SingleSequenceMode::Times(n) if n & 1 == 1 => {
+                (StartSequence::One, SequenceMode::Loop((n / 2) + 1))
+            }
+            SingleSequenceMode::Times(n) => (StartSequence::Zero, SequenceMode::Loop(n / 2)),
+            SingleSequenceMode::Infinite => (StartSequence::Zero, SequenceMode::Infinite),
+        };
+        self.sequencer.start(start_seq, times)
+    }
+
+    /// Stop playback. Disables the peripheral. Does NOT clear the last duty
+    /// cycle from the pin. Returns any sequences previously provided to
+    /// `start` so that they may be further mutated.
+    #[inline(always)]
+    pub fn stop(&self) {
+        self.sequencer.stop();
+    }
+}
+
+/// A composition of sequences that can be started and stopped.
+/// Takes at least one sequence along with its configuration.
+/// Optionally takes a second sequence and its configuration.
+/// In the case where no second sequence is provided then the first sequence
+/// is used.
+#[non_exhaustive]
+pub struct Sequencer<'d, 's, T: Instance> {
+    _pwm: &'s mut SequencePwm<'d, T>,
+    sequence0: Sequence<'s>,
+    sequence1: Option<Sequence<'s>>,
+}
+
+impl<'d, 's, T: Instance> Sequencer<'d, 's, T> {
+    /// Create a new double sequence. In the absence of sequence 1, sequence 0
+    /// will be used twice in the one loop.
+    pub fn new(
+        pwm: &'s mut SequencePwm<'d, T>,
+        sequence0: Sequence<'s>,
+        sequence1: Option<Sequence<'s>>,
+    ) -> Self {
+        Sequencer {
+            _pwm: pwm,
+            sequence0,
+            sequence1,
+        }
+    }
+
+    /// Start or restart playback. The sequence mode applies to both sequences combined as one.
+    #[inline(always)]
+    pub fn start(&self, start_seq: StartSequence, times: SequenceMode) -> Result<(), Error> {
+        let sequence0 = &self.sequence0;
+        let alt_sequence = self.sequence1.as_ref().unwrap_or(&self.sequence0);
+
+        slice_in_ram_or(sequence0.words, Error::DMABufferNotInDataMemory)?;
+        slice_in_ram_or(alt_sequence.words, Error::DMABufferNotInDataMemory)?;
+
+        if sequence0.words.len() > MAX_SEQUENCE_LEN || alt_sequence.words.len() > MAX_SEQUENCE_LEN {
+            return Err(Error::SequenceTooLong);
+        }
+
+        if let SequenceMode::Loop(0) = times {
+            return Err(Error::SequenceTimesAtLeastOne);
+        }
+
+        let _ = self.stop();
+
+        let r = T::regs();
+
+        r.seq0
+            .refresh
+            .write(|w| unsafe { w.bits(sequence0.config.refresh) });
+        r.seq0
+            .enddelay
+            .write(|w| unsafe { w.bits(sequence0.config.end_delay) });
+        r.seq0
+            .ptr
+            .write(|w| unsafe { w.bits(sequence0.words.as_ptr() as u32) });
+        r.seq0
+            .cnt
+            .write(|w| unsafe { w.bits(sequence0.words.len() as u32) });
+
+        r.seq1
+            .refresh
+            .write(|w| unsafe { w.bits(alt_sequence.config.refresh) });
+        r.seq1
+            .enddelay
+            .write(|w| unsafe { w.bits(alt_sequence.config.end_delay) });
+        r.seq1
+            .ptr
+            .write(|w| unsafe { w.bits(alt_sequence.words.as_ptr() as u32) });
+        r.seq1
+            .cnt
+            .write(|w| unsafe { w.bits(alt_sequence.words.len() as u32) });
+
+        r.enable.write(|w| w.enable().enabled());
+
+        // defensive before seqstart
+        compiler_fence(Ordering::SeqCst);
+
+        let seqstart_index = if start_seq == StartSequence::One {
+            1
+        } else {
+            0
+        };
+
+        match times {
+            // just the one time, no loop count
+            SequenceMode::Loop(n) => {
+                r.loop_.write(|w| unsafe { w.cnt().bits(n) });
+            }
+            // to play infinitely, repeat the sequence one time, then have loops done self trigger seq0 again
+            SequenceMode::Infinite => {
+                r.loop_.write(|w| unsafe { w.cnt().bits(0x1) });
+                r.shorts.write(|w| w.loopsdone_seqstart0().enabled());
+            }
+        }
+
+        // tasks_seqstart() doesn't exist in all svds so write its bit instead
+        r.tasks_seqstart[seqstart_index].write(|w| unsafe { w.bits(0x01) });
+
+        Ok(())
+    }
+
+    /// Stop playback. Disables the peripheral. Does NOT clear the last duty
+    /// cycle from the pin. Returns any sequences previously provided to
+    /// `start` so that they may be further mutated.
+    #[inline(always)]
+    pub fn stop(&self) {
+        let r = T::regs();
+
+        r.shorts.reset();
+
+        compiler_fence(Ordering::SeqCst);
+
+        // tasks_stop() doesn't exist in all svds so write its bit instead
+        r.tasks_stop.write(|w| unsafe { w.bits(0x01) });
+
+        r.enable.write(|w| w.enable().disabled());
+    }
+}
+
+impl<'d, 's, T: Instance> Drop for Sequencer<'d, 's, T> {
+    fn drop(&mut self) {
+        let _ = self.stop();
+    }
+}
+
+/// How many times to run a single sequence
 #[derive(Debug, Eq, PartialEq, Clone, Copy)]
-pub enum SequenceMode {
-    /// Run sequence n Times total
+pub enum SingleSequenceMode {
+    /// Run a single sequence n Times total.
     Times(u16),
     /// Repeat until `stop` is called.
     Infinite,
 }
 
+/// Which sequence to start a loop with
+#[derive(Debug, Eq, PartialEq, Clone, Copy)]
+pub enum StartSequence {
+    /// Start with Sequence 0
+    Zero,
+    /// Start with Sequence 1
+    One,
+}
+
+/// How many loops to run two sequences
+#[derive(Debug, Eq, PartialEq, Clone, Copy)]
+pub enum SequenceMode {
+    /// Run two sequences n loops i.e. (n * (seq0 + seq1.unwrap_or(seq0)))
+    Loop(u16),
+    /// Repeat until `stop` is called.
+    Infinite,
+}
+
 /// PWM Base clock is system clock (16MHz) divided by prescaler
 #[derive(Debug, Eq, PartialEq, Clone, Copy)]
 pub enum Prescaler {
diff --git a/examples/nrf/src/bin/pwm_double_sequence.rs b/examples/nrf/src/bin/pwm_double_sequence.rs
new file mode 100644
index 000000000..269015f4a
--- /dev/null
+++ b/examples/nrf/src/bin/pwm_double_sequence.rs
@@ -0,0 +1,46 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use defmt::*;
+use embassy::executor::Spawner;
+use embassy::time::{Duration, Timer};
+use embassy_nrf::gpio::NoPin;
+use embassy_nrf::pwm::{
+    Config, Prescaler, Sequence, SequenceConfig, SequenceMode, SequencePwm, Sequencer,
+    StartSequence,
+};
+use embassy_nrf::Peripherals;
+
+#[embassy::main]
+async fn main(_spawner: Spawner, p: Peripherals) {
+    let seq_words_0: [u16; 5] = [1000, 250, 100, 50, 0];
+    let seq_words_1: [u16; 4] = [50, 100, 250, 1000];
+
+    let mut config = Config::default();
+    config.prescaler = Prescaler::Div128;
+    // 1 period is 1000 * (128/16mhz = 0.000008s = 0.008ms) = 8us
+    // but say we want to hold the value for 5000ms
+    // so we want to repeat our value as many times as necessary until 5000ms passes
+    // want 5000/8 = 625 periods total to occur, so 624 (we get the one period for free remember)
+    let mut seq_config = SequenceConfig::default();
+    seq_config.refresh = 624;
+    // thus our sequence takes 5 * 5000ms or 25 seconds
+
+    let mut pwm = unwrap!(SequencePwm::new(
+        p.PWM0, p.P0_13, NoPin, NoPin, NoPin, config,
+    ));
+
+    let sequence_0 = Sequence::new(&seq_words_0, seq_config.clone());
+    let sequence_1 = Sequence::new(&seq_words_1, seq_config);
+    let sequencer = Sequencer::new(&mut pwm, sequence_0, Some(sequence_1));
+    unwrap!(sequencer.start(StartSequence::Zero, SequenceMode::Loop(1)));
+
+    // we can abort a sequence if we need to before its complete with pwm.stop()
+    // or stop is also implicitly called when the pwm peripheral is dropped
+    // when it goes out of scope
+    Timer::after(Duration::from_millis(40000)).await;
+    info!("pwm stopped early!");
+}
diff --git a/examples/nrf/src/bin/pwm_sequence.rs b/examples/nrf/src/bin/pwm_sequence.rs
index 56c865d1c..f06ea0b19 100644
--- a/examples/nrf/src/bin/pwm_sequence.rs
+++ b/examples/nrf/src/bin/pwm_sequence.rs
@@ -8,34 +8,31 @@ use defmt::*;
 use embassy::executor::Spawner;
 use embassy::time::{Duration, Timer};
 use embassy_nrf::gpio::NoPin;
-use embassy_nrf::pwm::{Prescaler, SequenceConfig, SequenceMode, SequencePwm};
+use embassy_nrf::pwm::{
+    Config, Prescaler, SequenceConfig, SequencePwm, SingleSequenceMode, SingleSequencer,
+};
 use embassy_nrf::Peripherals;
 
 #[embassy::main]
 async fn main(_spawner: Spawner, p: Peripherals) {
-    let seq_values_1: [u16; 5] = [1000, 250, 100, 50, 0];
-    let seq_values_2: [u16; 5] = [0, 50, 100, 250, 1000];
+    let seq_words: [u16; 5] = [1000, 250, 100, 50, 0];
 
-    let mut config = SequenceConfig::default();
+    let mut config = Config::default();
     config.prescaler = Prescaler::Div128;
     // 1 period is 1000 * (128/16mhz = 0.000008s = 0.008ms) = 8us
     // but say we want to hold the value for 5000ms
     // so we want to repeat our value as many times as necessary until 5000ms passes
     // want 5000/8 = 625 periods total to occur, so 624 (we get the one period for free remember)
-    config.refresh = 624;
+    let mut seq_config = SequenceConfig::default();
+    seq_config.refresh = 624;
     // thus our sequence takes 5 * 5000ms or 25 seconds
 
     let mut pwm = unwrap!(SequencePwm::new(
         p.PWM0, p.P0_13, NoPin, NoPin, NoPin, config,
     ));
-    let _ = pwm.start(&seq_values_1, SequenceMode::Infinite);
 
-    info!("pwm started!");
-
-    Timer::after(Duration::from_millis(20000)).await;
-    info!("pwm starting with another sequence!");
-
-    let _ = pwm.start(&seq_values_2, SequenceMode::Infinite);
+    let sequencer = SingleSequencer::new(&mut pwm, &seq_words, seq_config);
+    unwrap!(sequencer.start(SingleSequenceMode::Times(1)));
 
     // we can abort a sequence if we need to before its complete with pwm.stop()
     // or stop is also implicitly called when the pwm peripheral is dropped
diff --git a/examples/nrf/src/bin/pwm_sequence_ppi.rs b/examples/nrf/src/bin/pwm_sequence_ppi.rs
index f03c5716a..c25c5e10d 100644
--- a/examples/nrf/src/bin/pwm_sequence_ppi.rs
+++ b/examples/nrf/src/bin/pwm_sequence_ppi.rs
@@ -11,26 +11,28 @@ use embassy::executor::Spawner;
 use embassy_nrf::gpio::{Input, NoPin, Pull};
 use embassy_nrf::gpiote::{InputChannel, InputChannelPolarity};
 use embassy_nrf::ppi::Ppi;
-use embassy_nrf::pwm::{Prescaler, SequenceConfig, SequenceMode, SequencePwm};
+use embassy_nrf::pwm::{
+    Config, Prescaler, SequenceConfig, SequencePwm, SingleSequenceMode, SingleSequencer,
+};
 use embassy_nrf::Peripherals;
 
 #[embassy::main]
 async fn main(_spawner: Spawner, p: Peripherals) {
-    let seq_values: [u16; 5] = [1000, 250, 100, 50, 0];
+    let seq_words: [u16; 5] = [1000, 250, 100, 50, 0];
 
-    let mut config = SequenceConfig::default();
+    let mut config = Config::default();
     config.prescaler = Prescaler::Div128;
     // 1 period is 1000 * (128/16mhz = 0.000008s = 0.008ms) = 8us
     // but say we want to hold the value for 250ms 250ms/8 = 31.25 periods
     // so round to 31 - 1 (we get the one period for free remember)
     // thus our sequence takes 5 * 250ms or 1.25 seconds
-    config.refresh = 30;
+    let mut seq_config = SequenceConfig::default();
+    seq_config.refresh = 30;
 
     let mut pwm = unwrap!(SequencePwm::new(
         p.PWM0, p.P0_13, NoPin, NoPin, NoPin, config,
     ));
 
-    let _ = pwm.start(&seq_values, SequenceMode::Times(1));
     // pwm.stop() deconfigures pins, and then the task_start_seq0 task cant work
     // so its going to have to start running in order load the configuration
 
@@ -51,6 +53,9 @@ async fn main(_spawner: Spawner, p: Peripherals) {
     let start = unsafe { pwm.task_start_seq0() };
     let stop = unsafe { pwm.task_stop() };
 
+    let sequencer = SingleSequencer::new(&mut pwm, &seq_words, seq_config);
+    unwrap!(sequencer.start(SingleSequenceMode::Infinite));
+
     let mut ppi = Ppi::new_one_to_one(p.PPI_CH1, button1.event_in(), start);
     ppi.enable();
 
diff --git a/examples/nrf/src/bin/pwm_sequence_ws2812b.rs b/examples/nrf/src/bin/pwm_sequence_ws2812b.rs
new file mode 100644
index 000000000..d1a027a7e
--- /dev/null
+++ b/examples/nrf/src/bin/pwm_sequence_ws2812b.rs
@@ -0,0 +1,80 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use defmt::*;
+use embassy::executor::Spawner;
+use embassy::time::{Duration, Timer};
+use embassy_nrf::gpio::NoPin;
+use embassy_nrf::pwm::{
+    Config, Prescaler, SequenceConfig, SequenceLoad, SequencePwm, SingleSequenceMode,
+    SingleSequencer,
+};
+use embassy_nrf::Peripherals;
+
+// WS2812B LED light demonstration. Drives just one light.
+// The following reference on WS2812B may be of use:
+// https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf.
+// This demo lights up a single LED in blue. It then proceeds
+// to pulsate the LED rapidly.
+
+// In the following declarations, setting the high bit tells the PWM
+// to reverse polarity, which is what the WS2812B expects.
+
+const T1H: u16 = 0x8000 | 13; // Duty = 13/20 ticks (0.8us/1.25us) for a 1
+const T0H: u16 = 0x8000 | 7; // Duty 7/20 ticks (0.4us/1.25us) for a 0
+const RES: u16 = 0x8000;
+
+// Provides data to a WS2812b (Neopixel) LED and makes it go blue. The data
+// line is assumed to be P1_05.
+#[embassy::main]
+async fn main(_spawner: Spawner, p: Peripherals) {
+    let mut config = Config::default();
+    config.sequence_load = SequenceLoad::Common;
+    config.prescaler = Prescaler::Div1;
+    config.max_duty = 20; // 1.25us (1s / 16Mhz * 20)
+    let mut pwm = unwrap!(SequencePwm::new(
+        p.PWM0, p.P1_05, NoPin, NoPin, NoPin, config,
+    ));
+
+    // Declare the bits of 24 bits in a buffer we'll be
+    // mutating later.
+    let mut seq_words = [
+        T0H, T0H, T0H, T0H, T0H, T0H, T0H, T0H, // G
+        T0H, T0H, T0H, T0H, T0H, T0H, T0H, T0H, // R
+        T1H, T1H, T1H, T1H, T1H, T1H, T1H, T1H, // B
+        RES,
+    ];
+    let mut seq_config = SequenceConfig::default();
+    seq_config.end_delay = 799; // 50us (20 ticks * 40) - 1 tick because we've already got one RES;
+
+    let mut color_bit = 16;
+    let mut bit_value = T0H;
+
+    loop {
+        let sequences = SingleSequencer::new(&mut pwm, &seq_words, seq_config.clone());
+        unwrap!(sequences.start(SingleSequenceMode::Times(1)));
+
+        Timer::after(Duration::from_millis(50)).await;
+
+        if bit_value == T0H {
+            if color_bit == 20 {
+                bit_value = T1H;
+            } else {
+                color_bit += 1;
+            }
+        } else {
+            if color_bit == 16 {
+                bit_value = T0H;
+            } else {
+                color_bit -= 1;
+            }
+        }
+
+        drop(sequences);
+
+        seq_words[color_bit] = bit_value;
+    }
+}