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 <huntchr@gmail.com>

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!");
+}

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

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();
 

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;
+    }
+}