Merge #425

425: Implements continuous sampling for the nRF SAADC r=huntc a=huntc

Implements continuous sampling for the nRF SAADC and also renames `OneShot` to `Saadc`. The one-shot behaviour is retained with the `sample` method and a new `run_sampler` method is provided for efficiently (i.e. zero copying) sampler processing. A double buffer is used for continuously sampling, which is swapped appropriately.

A sample frequency is provided and will set the internal timer of the SAADC when there is just one channel being sampled. Otherwise, PPI will be used to hook up the TIMER peripheral to drive the sampling task. Two methods are provided for this: `run_task_sampler` and `run_task_sampler` with the latter available where the compiler sees that just one channel is configured. Note that we set up the PPI and timer behaviour outside of the `Saadc` for maximum flexibility.

A callback is provided to the `run_sampler` method. This is a synchronous callback that should return in a reasonably short space of time. The SAADC could stall if it does not. A reasonable practice is to perform a small amount of processing within the callback to yield a signal, perhaps via `mpsc`. In the case of `mpsc`, the `try_send` method becomes useful.

A new example has been provided to illustrate continuous sampling, along with multiple channels and external timing:

```rust
#[embassy::main]
async fn main(_spawner: Spawner, mut p: Peripherals) {
    let config = Config::default();
    let channel_1_config = ChannelConfig::single_ended(&mut p.P0_02);
    let channel_2_config = ChannelConfig::single_ended(&mut p.P0_03);
    let channel_3_config = ChannelConfig::single_ended(&mut p.P0_04);
    let mut saadc = Saadc::new(
        p.SAADC,
        interrupt::take!(SAADC),
        config,
        [channel_1_config, channel_2_config, channel_3_config],
    );

    let mut timer = Timer::new(p.TIMER0);
    timer.set_frequency(Frequency::F1MHz);
    timer.cc(0).write(100); // We want to sample at 10KHz
    timer.cc(0).short_compare_clear();

    let mut ppi = Ppi::new(p.PPI_CH0);
    ppi.set_event(timer.cc(0).event_compare());
    ppi.set_task(saadc.task_sample());
    ppi.enable();

    timer.start();

    let mut bufs = [[[0; 3]; 50]; 2];

    let mut c = 0;
    let mut a: i32 = 0;

    saadc
        .run_task_sampler(&mut bufs, move |buf| {
            for b in buf {
                a += b[0] as i32;
            }
            c += buf.len();
            if c > 10000 {
                a = a / c as i32;
                info!("channel 1: {=i32}", a);
                c = 0;
                a = 0;
            }
            SamplerState::Sampled
        })
        .await;
}
```

Co-authored-by: huntc <huntchr@gmail.com>

embassy-nrf/src/saadc.rs

@@ -10,6 +10,7 @@ use embassy_hal_common::unborrow;
 use futures::future::poll_fn;
 
 use crate::interrupt;
+use crate::ppi::Task;
 use crate::{pac, peripherals};
 
 use pac::{saadc, SAADC};
@@ -29,7 +30,7 @@ pub use saadc::{
 pub enum Error {}
 
 /// One-shot saadc. Continuous sample mode TODO.
-pub struct OneShot<'d, const N: usize> {
+pub struct Saadc<'d, const N: usize> {
     phantom: PhantomData<&'d mut peripherals::SAADC>,
 }
 
@@ -50,7 +51,7 @@ impl Default for Config {
     /// Default configuration for single channel sampling.
     fn default() -> Self {
         Self {
-            resolution: Resolution::_14BIT,
+            resolution: Resolution::_12BIT,
             oversample: Oversample::BYPASS,
         }
     }
@@ -98,7 +99,7 @@ impl<'d> ChannelConfig<'d> {
     ) -> Self {
         unborrow!(p_input, n_input);
         Self {
-            reference: Reference::VDD1_4,
+            reference: Reference::INTERNAL,
             gain: Gain::GAIN1_6,
             resistor: Resistor::BYPASS,
             time: Time::_10US,
@@ -109,7 +110,17 @@ impl<'d> ChannelConfig<'d> {
     }
 }
 
-impl<'d, const N: usize> OneShot<'d, N> {
+/// The state of a continuously running sampler. While it reflects
+/// the progress of a sampler, it also signals what should be done
+/// next. For example, if the sampler has stopped then the Saadc implementation
+/// can then tear down its infrastructure.
+#[derive(PartialEq)]
+pub enum SamplerState {
+    Sampled,
+    Stopped,
+}
+
+impl<'d, const N: usize> Saadc<'d, N> {
     pub fn new(
         _saadc: impl Unborrow<Target = peripherals::SAADC> + 'd,
         irq: impl Unborrow<Target = interrupt::SAADC> + 'd,
@@ -176,12 +187,18 @@ impl<'d, const N: usize> OneShot<'d, N> {
             r.intenclr.write(|w| w.end().clear());
             WAKER.wake();
         }
+
+        if r.events_started.read().bits() != 0 {
+            r.intenclr.write(|w| w.started().clear());
+            WAKER.wake();
+        }
     }
 
     fn regs() -> &'static saadc::RegisterBlock {
         unsafe { &*SAADC::ptr() }
     }
 
+    /// One shot sampling. The buffer must be the same size as the number of channels configured.
     pub async fn sample(&mut self, buf: &mut [i16; N]) {
         let r = Self::regs();
 
@@ -219,9 +236,148 @@ impl<'d, const N: usize> OneShot<'d, N> {
         })
         .await;
     }
+
+    /// Continuous sampling with double buffers.
+    ///
+    /// A task-driven approach to driving TASK_SAMPLE is expected. With a task
+    /// driven approach, multiple channels can be used.
+    ///
+    /// A sampler closure is provided that receives the buffer of samples, noting
+    /// that the size of this buffer can be less than the original buffer's size.
+    /// A command is return from the closure that indicates whether the sampling
+    /// should continue or stop.
+    pub async fn run_task_sampler<S, const N0: usize>(
+        &mut self,
+        bufs: &mut [[[i16; N]; N0]; 2],
+        sampler: S,
+    ) where
+        S: FnMut(&[[i16; N]]) -> SamplerState,
+    {
+        self.run_sampler(bufs, None, sampler).await;
+    }
+
+    async fn run_sampler<S, const N0: usize>(
+        &mut self,
+        bufs: &mut [[[i16; N]; N0]; 2],
+        sample_rate_divisor: Option<u16>,
+        mut sampler: S,
+    ) where
+        S: FnMut(&[[i16; N]]) -> SamplerState,
+    {
+        let r = Self::regs();
+
+        // Establish mode and sample rate
+        match sample_rate_divisor {
+            Some(sr) => {
+                r.samplerate.write(|w| unsafe {
+                    w.cc().bits(sr);
+                    w.mode().timers();
+                    w
+                });
+                r.tasks_sample.write(|w| unsafe { w.bits(1) }); // Need to kick-start the internal timer
+            }
+            None => r.samplerate.write(|w| unsafe {
+                w.cc().bits(0);
+                w.mode().task();
+                w
+            }),
+        }
+
+        // Set up the initial DMA
+        r.result
+            .ptr
+            .write(|w| unsafe { w.ptr().bits(bufs[0].as_mut_ptr() as u32) });
+        r.result
+            .maxcnt
+            .write(|w| unsafe { w.maxcnt().bits((N0 * N) as _) });
+
+        // Reset and enable the events
+        r.events_end.reset();
+        r.events_started.reset();
+        r.intenset.write(|w| {
+            w.end().set();
+            w.started().set();
+            w
+        });
+
+        // Don't reorder the ADC start event before the previous writes. Hopefully self
+        // wouldn't happen anyway.
+        compiler_fence(Ordering::SeqCst);
+
+        r.tasks_start.write(|w| unsafe { w.bits(1) });
+
+        let mut current_buffer = 0;
+
+        // Wait for events and complete when the sampler indicates it has had enough.
+        poll_fn(|cx| {
+            let r = Self::regs();
+
+            WAKER.register(cx.waker());
+
+            if r.events_end.read().bits() != 0 {
+                compiler_fence(Ordering::SeqCst);
+
+                r.events_end.reset();
+                r.intenset.write(|w| w.end().set());
+
+                if sampler(&bufs[current_buffer][0..r.result.amount.read().bits() as usize / N])
+                    == SamplerState::Sampled
+                {
+                    let next_buffer = 1 - current_buffer;
+                    current_buffer = next_buffer;
+                    r.tasks_start.write(|w| unsafe { w.bits(1) });
+                } else {
+                    return Poll::Ready(());
+                };
+            }
+
+            if r.events_started.read().bits() != 0 {
+                r.events_started.reset();
+                r.intenset.write(|w| w.started().set());
+
+                let next_buffer = 1 - current_buffer;
+                r.result
+                    .ptr
+                    .write(|w| unsafe { w.ptr().bits(bufs[next_buffer].as_mut_ptr() as u32) });
+            }
+
+            Poll::Pending
+        })
+        .await;
+    }
+
+    /// Return the sample task for use with PPI
+    pub fn task_sample(&self) -> Task {
+        let r = Self::regs();
+        Task::from_reg(&r.tasks_sample)
+    }
 }
 
-impl<'d, const N: usize> Drop for OneShot<'d, N> {
+impl<'d> Saadc<'d, 1> {
+    /// Continuous sampling on a single channel with double buffers.
+    ///
+    /// The internal clock is to be used with a sample rate expressed as a divisor of
+    /// 16MHz, ranging from 80..2047. For example, 1600 represnts a sample rate of 10KHz
+    /// given 16_000_000 / 10_000_000 = 1600.
+    ///
+    /// A sampler closure is provided that receives the buffer of samples, noting
+    /// that the size of this buffer can be less than the original buffer's size.
+    /// A command is return from the closure that indicates whether the sampling
+    /// should continue or stop.
+    pub async fn run_timer_sampler<S, const N0: usize>(
+        &mut self,
+        bufs: &mut [[[i16; 1]; N0]; 2],
+        sample_rate_divisor: u16,
+        sampler: S,
+    ) where
+        S: FnMut(&[[i16; 1]]) -> SamplerState,
+    {
+        self.run_sampler(bufs, Some(sample_rate_divisor), sampler)
+            .await;
+    }
+}
+
+impl<'d, const N: usize> Drop for Saadc<'d, N> {
     fn drop(&mut self) {
         let r = Self::regs();
         r.enable.write(|w| w.enable().disabled());

examples/nrf/src/bin/saadc.rs

@@ -7,7 +7,7 @@ mod example_common;
 use defmt::panic;
 use embassy::executor::Spawner;
 use embassy::time::{Duration, Timer};
-use embassy_nrf::saadc::{ChannelConfig, Config, OneShot};
+use embassy_nrf::saadc::{ChannelConfig, Config, Saadc};
 use embassy_nrf::{interrupt, Peripherals};
 use example_common::*;
 
@@ -15,7 +15,7 @@ use example_common::*;
 async fn main(_spawner: Spawner, mut p: Peripherals) {
     let config = Config::default();
     let channel_config = ChannelConfig::single_ended(&mut p.P0_02);
-    let mut saadc = OneShot::new(p.SAADC, interrupt::take!(SAADC), config, [channel_config]);
+    let mut saadc = Saadc::new(p.SAADC, interrupt::take!(SAADC), config, [channel_config]);
 
     loop {
         let mut buf = [0; 1];

examples/nrf/src/bin/saadc_continuous.rs

@@ -0,0 +1,62 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use defmt::panic;
+use embassy::executor::Spawner;
+use embassy_nrf::ppi::Ppi;
+use embassy_nrf::saadc::{ChannelConfig, Config, Saadc, SamplerState};
+use embassy_nrf::timer::{Frequency, Timer};
+use embassy_nrf::{interrupt, Peripherals};
+use example_common::*;
+
+// Demonstrates both continuous sampling and scanning multiple channels driven by a PPI linked timer
+
+#[embassy::main]
+async fn main(_spawner: Spawner, mut p: Peripherals) {
+    let config = Config::default();
+    let channel_1_config = ChannelConfig::single_ended(&mut p.P0_02);
+    let channel_2_config = ChannelConfig::single_ended(&mut p.P0_03);
+    let channel_3_config = ChannelConfig::single_ended(&mut p.P0_04);
+    let mut saadc = Saadc::new(
+        p.SAADC,
+        interrupt::take!(SAADC),
+        config,
+        [channel_1_config, channel_2_config, channel_3_config],
+    );
+
+    let mut timer = Timer::new(p.TIMER0);
+    timer.set_frequency(Frequency::F1MHz);
+    timer.cc(0).write(100); // We want to sample at 10KHz
+    timer.cc(0).short_compare_clear();
+
+    let mut ppi = Ppi::new(p.PPI_CH0);
+    ppi.set_event(timer.cc(0).event_compare());
+    ppi.set_task(saadc.task_sample());
+    ppi.enable();
+
+    timer.start();
+
+    let mut bufs = [[[0; 3]; 50]; 2];
+
+    let mut c = 0;
+    let mut a: i32 = 0;
+
+    saadc
+        .run_task_sampler(&mut bufs, move |buf| {
+            for b in buf {
+                a += b[0] as i32;
+            }
+            c += buf.len();
+            if c > 10000 {
+                a = a / c as i32;
+                info!("channel 1: {=i32}", a);
+                c = 0;
+                a = 0;
+            }
+            SamplerState::Sampled
+        })
+        .await;
+}