4 files changed, 370 insertions, 0 deletions

diff --git a/embassy-stm32/CHANGELOG.md b/embassy-stm32/CHANGELOG.md
index 4e55e1034..4d0559c0d 100644
--- a/embassy-stm32/CHANGELOG.md
+++ b/embassy-stm32/CHANGELOG.md
@@ -51,6 +51,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - chore: Updated stm32-metapac and stm32-data dependencies
 - feat: stm32/adc/v3: allow DMA reads to loop through enable channels
 - fix: Fix XSPI not disabling alternate bytes when they were previously enabled
+- feat: stm32/adc/v3: added support for Continuous DMA configuration 
 - fix: Fix stm32h7rs init when using external flash via XSPI
 - feat: Add Adc::new_with_clock() to configure analog clock
 - feat: Add GPDMA linked-list + ringbuffer support ([#3923](https://github.com/embassy-rs/embassy/pull/3923))
diff --git a/embassy-stm32/src/adc/ringbuffered_v3.rs b/embassy-stm32/src/adc/ringbuffered_v3.rs
new file mode 100644
index 000000000..0aee309e3
--- /dev/null
+++ b/embassy-stm32/src/adc/ringbuffered_v3.rs
@@ -0,0 +1,180 @@
+use core::marker::PhantomData;
+use core::sync::atomic::{Ordering, compiler_fence};
+
+use embassy_hal_internal::Peri;
+
+use crate::adc::{Instance, RxDma};
+use crate::dma::{ReadableRingBuffer, TransferOptions};
+use crate::rcc;
+
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub struct OverrunError;
+
+pub struct RingBufferedAdc<'d, T: Instance> {
+    pub _phantom: PhantomData<T>,
+    pub ring_buf: ReadableRingBuffer<'d, u16>,
+}
+
+impl<'d, T: Instance> RingBufferedAdc<'d, T> {
+    pub(crate) fn new(dma: Peri<'d, impl RxDma<T>>, dma_buf: &'d mut [u16]) -> Self {
+        //dma side setup
+        let opts = TransferOptions {
+            half_transfer_ir: true,
+            circular: true,
+            ..Default::default()
+        };
+
+        // Safety: we forget the struct before this function returns.
+        let request = dma.request();
+
+        let ring_buf =
+            unsafe { ReadableRingBuffer::new(dma, request, T::regs().dr().as_ptr() as *mut u16, dma_buf, opts) };
+
+        Self {
+            _phantom: PhantomData,
+            ring_buf,
+        }
+    }
+
+    #[inline]
+    fn start_continuous_sampling(&mut self) {
+        // Start adc conversion
+        T::regs().cr().modify(|reg| {
+            reg.set_adstart(true);
+        });
+        self.ring_buf.start();
+    }
+
+    #[inline]
+    pub fn stop_continuous_sampling(&mut self) {
+        // Stop adc conversion
+        if T::regs().cr().read().adstart() && !T::regs().cr().read().addis() {
+            T::regs().cr().modify(|reg| {
+                reg.set_adstp(true);
+            });
+            while T::regs().cr().read().adstart() {}
+        }
+    }
+    pub fn disable_adc(&mut self) {
+        self.stop_continuous_sampling();
+        self.ring_buf.clear();
+        self.ring_buf.request_pause();
+    }
+
+    pub fn teardown_adc(&mut self) {
+        self.disable_adc();
+
+        //disable dma control
+        #[cfg(not(any(adc_g0, adc_u0)))]
+        T::regs().cfgr().modify(|reg| {
+            reg.set_dmaen(false);
+        });
+        #[cfg(any(adc_g0, adc_u0))]
+        T::regs().cfgr1().modify(|reg| {
+            reg.set_dmaen(false);
+        });
+
+        //TODO: do we need to cleanup the DMA request here?
+
+        compiler_fence(Ordering::SeqCst);
+    }
+
+    /// Reads measurements from the DMA ring buffer.
+    ///
+    /// This method fills the provided `measurements` array with ADC readings from the DMA buffer.
+    /// The length of the `measurements` array should be exactly half of the DMA buffer length. Because interrupts are only generated if half or full DMA transfer completes.
+    ///
+    /// Each call to `read` will populate the `measurements` array in the same order as the channels defined with `sequence`.
+    /// There will be many sequences worth of measurements in this array because it only returns if at least half of the DMA buffer is filled.
+    /// For example if 2 channels are sampled `measurements` contain: `[sq0 sq1 sq0 sq1 sq0 sq1 ..]`.
+    ///
+    /// Note that the ADC Datarate can be very fast, it is suggested to use DMA mode inside tightly running tasks
+    /// Otherwise, you'll see constant Overrun errors occuring, this means that you're sampling too quickly for the task to handle, and you may need to increase the buffer size.
+    /// Example:
+    /// ```rust,ignore
+    /// const DMA_BUF_LEN: usize = 120;
+    /// use embassy_stm32::adc::{Adc, AdcChannel}
+    ///
+    /// let mut adc = Adc::new(p.ADC1);
+    /// let mut adc_pin0 = p.PA0.degrade_adc();
+    /// let mut adc_pin1 = p.PA1.degrade_adc();
+    /// let adc_dma_buf = [0u16; DMA_BUF_LEN];
+    ///
+    /// let mut ring_buffered_adc: RingBufferedAdc<embassy_stm32::peripherals::ADC1> = adc.into_ring_buffered(
+    ///     p.DMA2_CH0,
+    ///      adc_dma_buf, [
+    ///         (&mut *adc_pin0, SampleTime::CYCLES160_5),
+    ///         (&mut *adc_pin1, SampleTime::CYCLES160_5),
+    ///     ].into_iter());
+    ///
+    ///
+    /// let mut measurements = [0u16; DMA_BUF_LEN / 2];
+    /// loop {
+    ///     match ring_buffered_adc.read(&mut measurements).await {
+    ///         Ok(_) => {
+    ///             defmt::info!("adc1: {}", measurements);
+    ///         }
+    ///         Err(e) => {
+    ///             defmt::warn!("Error: {:?}", e);
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    ///
+    /// [`teardown_adc`]: #method.teardown_adc
+    /// [`start_continuous_sampling`]: #method.start_continuous_sampling
+    pub async fn read(&mut self, measurements: &mut [u16]) -> Result<usize, OverrunError> {
+        assert_eq!(
+            self.ring_buf.capacity() / 2,
+            measurements.len(),
+            "Buffer size must be half the size of the ring buffer"
+        );
+
+        let r = T::regs();
+
+        // Start background receive if it was not already started
+        if !r.cr().read().adstart() {
+            self.start_continuous_sampling();
+        }
+
+        self.ring_buf.read_exact(measurements).await.map_err(|_| OverrunError)
+    }
+
+    /// Read bytes that are readily available in the ring buffer.
+    /// If no bytes are currently available in the buffer the call waits until the some
+    /// bytes are available (at least one byte and at most half the buffer size)
+    ///
+    /// Background receive is started if `start_continuous_sampling()` has not been previously called.
+    ///
+    /// Receive in the background is terminated if an error is returned.
+    /// It must then manually be started again by calling `start_continuous_sampling()` or by re-calling `blocking_read()`.
+    pub fn blocking_read(&mut self, buf: &mut [u16]) -> Result<usize, OverrunError> {
+        let r = T::regs();
+
+        // Start background receive if it was not already started
+        if !r.cr().read().adstart() {
+            self.start_continuous_sampling();
+        }
+
+        loop {
+            match self.ring_buf.read(buf) {
+                Ok((0, _)) => {}
+                Ok((len, _)) => {
+                    return Ok(len);
+                }
+                Err(_) => {
+                    self.stop_continuous_sampling();
+                    return Err(OverrunError);
+                }
+            }
+        }
+    }
+}
+
+impl<T: Instance> Drop for RingBufferedAdc<'_, T> {
+    fn drop(&mut self) {
+        self.teardown_adc();
+        rcc::disable::<T>();
+    }
+}
diff --git a/embassy-stm32/src/adc/v3.rs b/embassy-stm32/src/adc/v3.rs
index 47632263b..d9a3ce21d 100644
--- a/embassy-stm32/src/adc/v3.rs
+++ b/embassy-stm32/src/adc/v3.rs
@@ -12,6 +12,13 @@ pub use pac::adc::vals::{Ovsr, Ovss, Presc};
 use super::{
     Adc, AdcChannel, AnyAdcChannel, Instance, Resolution, RxDma, SampleTime, SealedAdcChannel, blocking_delay_us,
 };
+
+#[cfg(any(adc_v3, adc_g0, adc_u0))]
+mod ringbuffered_v3;
+
+#[cfg(any(adc_v3, adc_g0, adc_u0))]
+use ringbuffered_v3::RingBufferedAdc;
+
 use crate::dma::Transfer;
 use crate::{Peri, pac, rcc};
 
@@ -559,6 +566,137 @@ impl<'d, T: Instance> Adc<'d, T> {
         });
     }
 
+    /// Configures the ADC to use a DMA ring buffer for continuous data acquisition.
+    ///
+    /// The `dma_buf` should be large enough to prevent DMA buffer overrun.
+    /// The length of the `dma_buf` should be a multiple of the ADC channel count.
+    /// For example, if 3 channels are measured, its length can be 3 * 40 = 120 measurements.
+    ///
+    /// `read` method is used to read out measurements from the DMA ring buffer, and its buffer should be exactly half of the `dma_buf` length.
+    /// It is critical to call `read` frequently to prevent DMA buffer overrun.
+    ///
+    /// [`read`]: #method.read
+    #[cfg(any(adc_v3, adc_g0, adc_u0))]
+    pub fn into_ring_buffered<'a>(
+        &mut self,
+        dma: Peri<'a, impl RxDma<T>>,
+        dma_buf: &'a mut [u16],
+        sequence: impl ExactSizeIterator<Item = (&'a mut AnyAdcChannel<T>, SampleTime)>,
+    ) -> RingBufferedAdc<'a, T> {
+        assert!(!dma_buf.is_empty() && dma_buf.len() <= 0xFFFF);
+        assert!(sequence.len() != 0, "Asynchronous read sequence cannot be empty");
+        assert!(
+            sequence.len() <= 16,
+            "Asynchronous read sequence cannot be more than 16 in length"
+        );
+        // reset conversions and enable the adc
+        Self::cancel_conversions();
+        self.enable();
+
+        //adc side setup
+
+        // Set sequence length
+        #[cfg(not(any(adc_g0, adc_u0)))]
+        T::regs().sqr1().modify(|w| {
+            w.set_l(sequence.len() as u8 - 1);
+        });
+
+        #[cfg(adc_g0)]
+        {
+            let mut sample_times = Vec::<SampleTime, SAMPLE_TIMES_CAPACITY>::new();
+
+            T::regs().chselr().write(|chselr| {
+                T::regs().smpr().write(|smpr| {
+                    for (channel, sample_time) in sequence {
+                        chselr.set_chsel(channel.channel.into(), true);
+                        if let Some(i) = sample_times.iter().position(|&t| t == sample_time) {
+                            smpr.set_smpsel(channel.channel.into(), (i as u8).into());
+                        } else {
+                            smpr.set_sample_time(sample_times.len(), sample_time);
+                            if let Err(_) = sample_times.push(sample_time) {
+                                panic!(
+                                    "Implementation is limited to {} unique sample times among all channels.",
+                                    SAMPLE_TIMES_CAPACITY
+                                );
+                            }
+                        }
+                    }
+                })
+            });
+        }
+        #[cfg(not(adc_g0))]
+        {
+            #[cfg(adc_u0)]
+            let mut channel_mask = 0;
+
+            // Configure channels and ranks
+            for (_i, (channel, sample_time)) in sequence.enumerate() {
+                Self::configure_channel(channel, sample_time);
+
+                // Each channel is sampled according to sequence
+                #[cfg(not(any(adc_g0, adc_u0)))]
+                match _i {
+                    0..=3 => {
+                        T::regs().sqr1().modify(|w| {
+                            w.set_sq(_i, channel.channel());
+                        });
+                    }
+                    4..=8 => {
+                        T::regs().sqr2().modify(|w| {
+                            w.set_sq(_i - 4, channel.channel());
+                        });
+                    }
+                    9..=13 => {
+                        T::regs().sqr3().modify(|w| {
+                            w.set_sq(_i - 9, channel.channel());
+                        });
+                    }
+                    14..=15 => {
+                        T::regs().sqr4().modify(|w| {
+                            w.set_sq(_i - 14, channel.channel());
+                        });
+                    }
+                    _ => unreachable!(),
+                }
+
+                #[cfg(adc_u0)]
+                {
+                    channel_mask |= 1 << channel.channel();
+                }
+            }
+
+            // On G0 and U0 enabled channels are sampled from 0 to last channel.
+            // It is possible to add up to 8 sequences if CHSELRMOD = 1.
+            // However for supporting more than 8 channels alternative CHSELRMOD = 0 approach is used.
+            #[cfg(adc_u0)]
+            T::regs().chselr().modify(|reg| {
+                reg.set_chsel(channel_mask);
+            });
+        }
+        // Set continuous mode with Circular dma.
+        // Clear overrun flag before starting transfer.
+        T::regs().isr().modify(|reg| {
+            reg.set_ovr(true);
+        });
+
+        #[cfg(not(any(adc_g0, adc_u0)))]
+        T::regs().cfgr().modify(|reg| {
+            reg.set_discen(false);
+            reg.set_cont(true);
+            reg.set_dmacfg(Dmacfg::CIRCULAR);
+            reg.set_dmaen(true);
+        });
+        #[cfg(any(adc_g0, adc_u0))]
+        T::regs().cfgr1().modify(|reg| {
+            reg.set_discen(false);
+            reg.set_cont(true);
+            reg.set_dmacfg(Dmacfg::CIRCULAR);
+            reg.set_dmaen(true);
+        });
+
+        RingBufferedAdc::new(dma, dma_buf)
+    }
+
     #[cfg(not(adc_g0))]
     fn configure_channel(channel: &mut impl AdcChannel<T>, sample_time: SampleTime) {
         // RM0492, RM0481, etc.
diff --git a/examples/stm32l4/src/bin/adc_dma.rs b/examples/stm32l4/src/bin/adc_dma.rs
new file mode 100644
index 000000000..7a9200edd
--- /dev/null
+++ b/examples/stm32l4/src/bin/adc_dma.rs
@@ -0,0 +1,51 @@
+#![no_std]
+#![no_main]
+
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_stm32::Config;
+use embassy_stm32::adc::{Adc, AdcChannel, SampleTime};
+use {defmt_rtt as _, panic_probe as _};
+
+const DMA_BUF_LEN: usize = 512;
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    info!("Hello World!");
+
+    let mut config = Config::default();
+    {
+        use embassy_stm32::rcc::*;
+        config.rcc.mux.adcsel = mux::Adcsel::SYS;
+    }
+    let p = embassy_stm32::init(config);
+
+    let mut adc = Adc::new(p.ADC1);
+    let mut adc_pin0 = p.PA0.degrade_adc();
+    let mut adc_pin1 = p.PA1.degrade_adc();
+    let mut adc_dma_buf = [0u16; DMA_BUF_LEN];
+    let mut measurements = [0u16; DMA_BUF_LEN / 2];
+    let mut ring_buffered_adc = adc.into_ring_buffered(
+        p.DMA1_CH1,
+        &mut adc_dma_buf,
+        [
+            (&mut adc_pin0, SampleTime::CYCLES640_5),
+            (&mut adc_pin1, SampleTime::CYCLES640_5),
+        ]
+        .into_iter(),
+    );
+
+    info!("starting measurement loop");
+    loop {
+        match ring_buffered_adc.read(&mut measurements).await {
+            Ok(_) => {
+                //note: originally there was a print here showing all the samples,
+                //but even that takes too much time and would cause adc overruns
+                info!("adc1 first 10 samples: {}", measurements[0..10]);
+            }
+            Err(e) => {
+                warn!("Error: {:?}", e);
+            }
+        }
+    }
+}