Low power UART driver

embassy-nrf/Cargo.toml

@@ -26,6 +26,7 @@ log = { version = "0.4.11", optional = true }
 cortex-m-rt = "0.6.13"
 cortex-m        = { version = "0.6.4" }
 embedded-hal    = { version = "0.2.4" }
+embedded-dma    = { version = "0.1.2" }
 
 nrf52810-pac  = { version = "0.9.0", optional = true }
 nrf52811-pac  = { version = "0.9.1", optional = true }

embassy-nrf/src/lib.rs

@@ -57,5 +57,6 @@ pub mod interrupt;
 #[cfg(feature = "52840")]
 pub mod qspi;
 pub mod rtc;
+pub mod uarte;
 
 pub use cortex_m_rt::interrupt;

embassy-nrf/src/uarte.rs

@@ -0,0 +1,418 @@
+//! Async low power UARTE.
+//!
+//! The peripheral is automatically enabled and disabled as required to save power.
+//! Lowest power consumption can only be guaranteed if the send receive futures
+//! are dropped correctly (e.g. not using `mem::forget()`).
+
+use core::future::Future;
+use core::ops::Deref;
+use core::sync::atomic::{compiler_fence, Ordering};
+use core::task::{Context, Poll};
+
+use embassy::util::Signal;
+use embedded_dma::{ReadBuffer, WriteBuffer};
+
+use crate::fmt::{assert, *};
+#[cfg(any(feature = "52833", feature = "52840"))]
+use crate::hal::gpio::Port as GpioPort;
+use crate::hal::pac;
+use crate::hal::prelude::*;
+use crate::hal::target_constants::EASY_DMA_SIZE;
+use crate::interrupt;
+use crate::interrupt::OwnedInterrupt;
+
+pub use crate::hal::uarte::Pins;
+// Re-export SVD variants to allow user to directly set values.
+pub use pac::uarte0::{baudrate::BAUDRATE_A as Baudrate, config::PARITY_A as Parity};
+
+/// Interface to the UARTE peripheral
+pub struct Uarte<T>
+where
+    T: Instance,
+{
+    instance: T,
+    irq: T::Interrupt,
+    pins: Pins,
+}
+
+pub struct State {
+    tx_done: Signal<()>,
+    rx_done: Signal<u32>,
+}
+
+// TODO: Remove when https://github.com/nrf-rs/nrf-hal/pull/276 has landed
+#[cfg(any(feature = "52833", feature = "52840"))]
+fn port_bit(port: GpioPort) -> bool {
+    match port {
+        GpioPort::Port0 => false,
+        GpioPort::Port1 => true,
+    }
+}
+
+impl<T> Uarte<T>
+where
+    T: Instance,
+{
+    /// Creates the interface to a UARTE instance.
+    /// Sets the baud rate, parity and assigns the pins to the UARTE peripheral.
+    ///
+    /// # Unsafe
+    ///
+    /// The returned API is safe unless you use `mem::forget` (or similar safe mechanisms)
+    /// on stack allocated buffers which which have been passed to [`send()`](Uarte::send)
+    /// or [`receive`](Uarte::receive).
+    #[allow(unused_unsafe)]
+    pub unsafe fn new(
+        uarte: T,
+        irq: T::Interrupt,
+        mut pins: Pins,
+        parity: Parity,
+        baudrate: Baudrate,
+    ) -> Self {
+        assert!(uarte.enable.read().enable().is_disabled());
+
+        uarte.psel.rxd.write(|w| {
+            let w = unsafe { w.pin().bits(pins.rxd.pin()) };
+            #[cfg(any(feature = "52833", feature = "52840"))]
+            let w = w.port().bit(port_bit(pins.rxd.port()));
+            w.connect().connected()
+        });
+
+        pins.txd.set_high().unwrap();
+        uarte.psel.txd.write(|w| {
+            let w = unsafe { w.pin().bits(pins.txd.pin()) };
+            #[cfg(any(feature = "52833", feature = "52840"))]
+            let w = w.port().bit(port_bit(pins.txd.port()));
+            w.connect().connected()
+        });
+
+        // Optional pins
+        uarte.psel.cts.write(|w| {
+            if let Some(ref pin) = pins.cts {
+                let w = unsafe { w.pin().bits(pin.pin()) };
+                #[cfg(any(feature = "52833", feature = "52840"))]
+                let w = w.port().bit(port_bit(pin.port()));
+                w.connect().connected()
+            } else {
+                w.connect().disconnected()
+            }
+        });
+
+        uarte.psel.rts.write(|w| {
+            if let Some(ref pin) = pins.rts {
+                let w = unsafe { w.pin().bits(pin.pin()) };
+                #[cfg(any(feature = "52833", feature = "52840"))]
+                let w = w.port().bit(port_bit(pin.port()));
+                w.connect().connected()
+            } else {
+                w.connect().disconnected()
+            }
+        });
+
+        uarte.baudrate.write(|w| w.baudrate().variant(baudrate));
+        uarte.config.write(|w| w.parity().variant(parity));
+
+        // Enable interrupts
+        uarte.events_endtx.reset();
+        uarte.events_endrx.reset();
+        uarte
+            .intenset
+            .write(|w| w.endtx().set().txstopped().set().endrx().set().rxto().set());
+
+        // Register ISR
+        irq.set_handler(Self::on_irq);
+        irq.unpend();
+        irq.enable();
+
+        Uarte {
+            instance: uarte,
+            irq,
+            pins,
+        }
+    }
+
+    pub fn free(self) -> (T, T::Interrupt, Pins) {
+        (self.instance, self.irq, self.pins)
+    }
+
+    fn enable(&mut self) {
+        trace!("enable");
+        self.instance.enable.write(|w| w.enable().enabled());
+    }
+
+    /// Sends serial data.
+    ///
+    /// `tx_buffer` is marked as static as per `embedded-dma` requirements.
+    /// It it safe to use a buffer with a non static lifetime if memory is not
+    /// reused until the future has finished.
+    pub fn send<'a, B>(&'a mut self, tx_buffer: B) -> SendFuture<'a, T, B>
+    where
+        B: ReadBuffer<Word = u8>,
+    {
+        // Panic if TX is running which can happen if the user has called
+        // `mem::forget()` on a previous future after polling it once.
+        assert!(!self.tx_started());
+
+        self.enable();
+
+        SendFuture {
+            uarte: self,
+            buf: tx_buffer,
+        }
+    }
+
+    fn tx_started(&self) -> bool {
+        self.instance.events_txstarted.read().bits() != 0
+    }
+
+    /// Receives serial data.
+    ///
+    /// The future is pending until the buffer is completely filled.
+    /// A common pattern is to use [`stop()`](ReceiveFuture::stop) to cancel
+    /// unfinished transfers after a timeout to prevent lockup when no more data
+    /// is incoming.
+    ///
+    /// `rx_buffer` is marked as static as per `embedded-dma` requirements.
+    /// It it safe to use a buffer with a non static lifetime if memory is not
+    /// reused until the future has finished.
+    pub fn receive<'a, B>(&'a mut self, rx_buffer: B) -> ReceiveFuture<'a, T, B>
+    where
+        B: WriteBuffer<Word = u8>,
+    {
+        // Panic if RX is running which can happen if the user has called
+        // `mem::forget()` on a previous future after polling it once.
+        assert!(!self.rx_started());
+
+        self.enable();
+
+        ReceiveFuture {
+            uarte: self,
+            buf: Some(rx_buffer),
+        }
+    }
+
+    fn rx_started(&self) -> bool {
+        self.instance.events_rxstarted.read().bits() != 0
+    }
+
+    unsafe fn on_irq() {
+        let uarte = &*pac::UARTE0::ptr();
+
+        let mut try_disable = false;
+
+        if uarte.events_endtx.read().bits() != 0 {
+            uarte.events_endtx.reset();
+            trace!("endtx");
+            compiler_fence(Ordering::SeqCst);
+            T::state().tx_done.signal(());
+        }
+
+        if uarte.events_txstopped.read().bits() != 0 {
+            uarte.events_txstopped.reset();
+            trace!("txstopped");
+            try_disable = true;
+        }
+
+        if uarte.events_endrx.read().bits() != 0 {
+            uarte.events_endrx.reset();
+            trace!("endrx");
+            let len = uarte.rxd.amount.read().bits();
+            compiler_fence(Ordering::SeqCst);
+            T::state().rx_done.signal(len);
+        }
+
+        if uarte.events_rxto.read().bits() != 0 {
+            uarte.events_rxto.reset();
+            trace!("rxto");
+            try_disable = true;
+        }
+
+        // Disable the peripheral if not active.
+        if try_disable
+            && uarte.events_txstarted.read().bits() == 0
+            && uarte.events_rxstarted.read().bits() == 0
+        {
+            trace!("disable");
+            uarte.enable.write(|w| w.enable().disabled());
+        }
+    }
+}
+
+/// Future for the [`Uarte::send()`] method.
+pub struct SendFuture<'a, T, B>
+where
+    T: Instance,
+{
+    uarte: &'a Uarte<T>,
+    buf: B,
+}
+
+impl<'a, T, B> Drop for SendFuture<'a, T, B>
+where
+    T: Instance,
+{
+    fn drop(self: &mut Self) {
+        if self.uarte.tx_started() {
+            trace!("stoptx");
+
+            // Stop the transmitter to minimize the current consumption.
+            self.uarte.instance.events_txstarted.reset();
+            self.uarte
+                .instance
+                .tasks_stoptx
+                .write(|w| unsafe { w.bits(1) });
+            T::state().tx_done.blocking_wait();
+        }
+    }
+}
+
+impl<'a, T, B> Future for SendFuture<'a, T, B>
+where
+    T: Instance,
+    B: ReadBuffer<Word = u8>,
+{
+    type Output = ();
+
+    fn poll(self: core::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        let Self { uarte, buf } = unsafe { self.get_unchecked_mut() };
+
+        if !uarte.tx_started() {
+            let uarte = &uarte.instance;
+
+            T::state().tx_done.reset();
+
+            let (ptr, len) = unsafe { buf.read_buffer() };
+            assert!(len <= EASY_DMA_SIZE);
+            // TODO: panic if buffer is not in SRAM
+
+            compiler_fence(Ordering::SeqCst);
+            uarte.txd.ptr.write(|w| unsafe { w.ptr().bits(ptr as u32) });
+            uarte
+                .txd
+                .maxcnt
+                .write(|w| unsafe { w.maxcnt().bits(len as _) });
+
+            trace!("starttx");
+            uarte.tasks_starttx.write(|w| unsafe { w.bits(1) });
+        }
+
+        T::state().tx_done.poll_wait(cx)
+    }
+}
+
+/// Future for the [`Uarte::receive()`] method.
+pub struct ReceiveFuture<'a, T, B>
+where
+    T: Instance,
+{
+    uarte: &'a Uarte<T>,
+    buf: Option<B>,
+}
+
+impl<'a, T, B> Drop for ReceiveFuture<'a, T, B>
+where
+    T: Instance,
+{
+    fn drop(self: &mut Self) {
+        if self.uarte.rx_started() {
+            trace!("stoprx");
+
+            self.uarte.instance.events_rxstarted.reset();
+            self.uarte
+                .instance
+                .tasks_stoprx
+                .write(|w| unsafe { w.bits(1) });
+            T::state().rx_done.blocking_wait();
+        }
+    }
+}
+
+impl<'a, T, B> Future for ReceiveFuture<'a, T, B>
+where
+    T: Instance,
+    B: WriteBuffer<Word = u8>,
+{
+    type Output = B;
+
+    fn poll(self: core::pin::Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<B> {
+        let Self { uarte, buf } = unsafe { self.get_unchecked_mut() };
+
+        if !uarte.rx_started() {
+            let uarte = &uarte.instance;
+
+            T::state().rx_done.reset();
+
+            let (ptr, len) = unsafe { buf.as_mut().unwrap().write_buffer() };
+            assert!(len <= EASY_DMA_SIZE);
+
+            compiler_fence(Ordering::SeqCst);
+            uarte.rxd.ptr.write(|w| unsafe { w.ptr().bits(ptr as u32) });
+            uarte
+                .rxd
+                .maxcnt
+                .write(|w| unsafe { w.maxcnt().bits(len as _) });
+
+            trace!("startrx");
+            uarte.tasks_startrx.write(|w| unsafe { w.bits(1) });
+        }
+
+        T::state()
+            .rx_done
+            .poll_wait(cx)
+            .map(|_| buf.take().unwrap())
+    }
+}
+
+/// Future for the [`receive()`] method.
+impl<'a, T, B> ReceiveFuture<'a, T, B>
+where
+    T: Instance,
+{
+    /// Stops the ongoing reception and returns the number of bytes received.
+    pub async fn stop(mut self) -> (B, usize) {
+        let buf = self.buf.take().unwrap();
+        drop(self);
+        let len = T::state().rx_done.wait().await;
+        (buf, len as _)
+    }
+}
+
+mod private {
+    pub trait Sealed {}
+}
+
+pub trait Instance: Deref<Target = pac::uarte0::RegisterBlock> + Sized + private::Sealed {
+    type Interrupt: OwnedInterrupt;
+
+    #[doc(hidden)]
+    fn state() -> &'static State;
+}
+
+static UARTE0_STATE: State = State {
+    tx_done: Signal::new(),
+    rx_done: Signal::new(),
+};
+impl private::Sealed for pac::UARTE0 {}
+impl Instance for pac::UARTE0 {
+    type Interrupt = interrupt::UARTE0_UART0Interrupt;
+
+    fn state() -> &'static State {
+        &UARTE0_STATE
+    }
+}
+
+#[cfg(any(feature = "52833", feature = "52840", feature = "9160"))]
+static UARTE1_STATE: State = State {
+    tx_done: Signal::new(),
+    rx_done: Signal::new(),
+};
+#[cfg(any(feature = "52833", feature = "52840", feature = "9160"))]
+impl private::Sealed for pac::UARTE1 {}
+#[cfg(any(feature = "52833", feature = "52840", feature = "9160"))]
+impl Instance for pac::UARTE1 {
+    type Interrupt = interrupt::UARTE1Interrupt;
+
+    fn state() -> &'static State {
+        &UARTE1_STATE
+    }
+}

examples/src/bin/buffered_uart.rs

@@ -0,0 +1,84 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use example_common::*;
+
+use cortex_m_rt::entry;
+use defmt::panic;
+use futures::pin_mut;
+use nrf52840_hal::gpio;
+
+use embassy::executor::{task, Executor};
+use embassy::io::{AsyncBufRead, AsyncBufReadExt, AsyncWrite, AsyncWriteExt};
+use embassy::util::Forever;
+use embassy_nrf::buffered_uarte;
+use embassy_nrf::interrupt;
+
+#[task]
+async fn run() {
+    let p = unwrap!(embassy_nrf::pac::Peripherals::take());
+
+    let port0 = gpio::p0::Parts::new(p.P0);
+
+    let pins = buffered_uarte::Pins {
+        rxd: port0.p0_08.into_floating_input().degrade(),
+        txd: port0
+            .p0_06
+            .into_push_pull_output(gpio::Level::Low)
+            .degrade(),
+        cts: None,
+        rts: None,
+    };
+
+    let irq = interrupt::take!(UARTE0_UART0);
+    let u = buffered_uarte::BufferedUarte::new(
+        p.UARTE0,
+        irq,
+        pins,
+        buffered_uarte::Parity::EXCLUDED,
+        buffered_uarte::Baudrate::BAUD115200,
+    );
+    pin_mut!(u);
+
+    info!("uarte initialized!");
+
+    unwrap!(u.write_all(b"Hello!\r\n").await);
+    info!("wrote hello in uart!");
+
+    // Simple demo, reading 8-char chunks and echoing them back reversed.
+    loop {
+        info!("reading...");
+        let mut buf = [0u8; 8];
+        unwrap!(u.read_exact(&mut buf).await);
+        info!("read done, got {:[u8]}", buf);
+
+        // Reverse buf
+        for i in 0..4 {
+            let tmp = buf[i];
+            buf[i] = buf[7 - i];
+            buf[7 - i] = tmp;
+        }
+
+        info!("writing...");
+        unwrap!(u.write_all(&buf).await);
+        info!("write done");
+    }
+}
+
+static EXECUTOR: Forever<Executor> = Forever::new();
+
+#[entry]
+fn main() -> ! {
+    info!("Hello World!");
+
+    let executor = EXECUTOR.put(Executor::new(cortex_m::asm::sev));
+    unwrap!(executor.spawn(run()));
+
+    loop {
+        executor.run();
+        cortex_m::asm::wfe();
+    }
+}

examples/src/bin/uart.rs

@@ -8,22 +8,76 @@ use example_common::*;
 
 use cortex_m_rt::entry;
 use defmt::panic;
-use futures::pin_mut;
+use embassy::executor::{task, Executor};
+use embassy::time::{Duration, Timer};
+use embassy::util::Forever;
+use embassy_nrf::{interrupt, pac, rtc, uarte};
+use futures::future::{select, Either};
+use nrf52840_hal::clocks;
 use nrf52840_hal::gpio;
 
-use embassy::executor::{task, Executor};
-use embassy::io::{AsyncBufRead, AsyncBufReadExt, AsyncWrite, AsyncWriteExt};
-use embassy::util::Forever;
-use embassy_nrf::buffered_uarte;
-use embassy_nrf::interrupt;
-
 #[task]
-async fn run() {
+async fn run(mut uart: uarte::Uarte<pac::UARTE0>) {
+    info!("uarte initialized!");
+
+    // Message must be in SRAM
+    let mut buf = [0; 8];
+    buf.copy_from_slice(b"Hello!\r\n");
+
+    uart.send(&buf).await;
+    info!("wrote hello in uart!");
+
+    info!("reading...");
+    loop {
+        let received = match select(
+            uart.receive(&mut buf),
+            Timer::after(Duration::from_millis(10)),
+        )
+        .await
+        {
+            Either::Left((buf, _)) => buf,
+            Either::Right((_, read)) => {
+                let (buf, n) = read.stop().await;
+                &buf[..n]
+            }
+        };
+
+        if received.len() > 0 {
+            info!("read done, got {:[u8]}", received);
+
+            // Echo back received data
+            uart.send(received).await;
+        }
+    }
+}
+
+static RTC: Forever<rtc::RTC<pac::RTC1>> = Forever::new();
+static ALARM: Forever<rtc::Alarm<pac::RTC1>> = Forever::new();
+static EXECUTOR: Forever<Executor> = Forever::new();
+
+#[entry]
+fn main() -> ! {
+    info!("Hello World!");
+
     let p = unwrap!(embassy_nrf::pac::Peripherals::take());
 
+    clocks::Clocks::new(p.CLOCK)
+        .enable_ext_hfosc()
+        .set_lfclk_src_external(clocks::LfOscConfiguration::NoExternalNoBypass)
+        .start_lfclk();
+
+    let rtc = RTC.put(rtc::RTC::new(p.RTC1, interrupt::take!(RTC1)));
+    rtc.start();
+
+    unsafe { embassy::time::set_clock(rtc) };
+
+    let alarm = ALARM.put(rtc.alarm0());
+    let executor = EXECUTOR.put(Executor::new_with_alarm(alarm, cortex_m::asm::sev));
+
+    // Init UART
     let port0 = gpio::p0::Parts::new(p.P0);
 
-    let pins = buffered_uarte::Pins {
+    let pins = uarte::Pins {
         rxd: port0.p0_08.into_floating_input().degrade(),
         txd: port0
             .p0_06
@@ -33,49 +87,18 @@ async fn run() {
         rts: None,
     };
 
-    let irq = interrupt::take!(UARTE0_UART0);
-    let u = buffered_uarte::BufferedUarte::new(
+    // NOTE(unsafe): Safe becasue we do not use `mem::forget` anywhere.
+    let uart = unsafe {
+        uarte::Uarte::new(
             p.UARTE0,
-        irq,
+            interrupt::take!(UARTE0_UART0),
             pins,
-        buffered_uarte::Parity::EXCLUDED,
-        buffered_uarte::Baudrate::BAUD115200,
-    );
-    pin_mut!(u);
+            uarte::Parity::EXCLUDED,
+            uarte::Baudrate::BAUD115200,
+        )
+    };
 
-    info!("uarte initialized!");
-
-    unwrap!(u.write_all(b"Hello!\r\n").await);
-    info!("wrote hello in uart!");
-
-    // Simple demo, reading 8-char chunks and echoing them back reversed.
-    loop {
-        info!("reading...");
-        let mut buf = [0u8; 8];
-        unwrap!(u.read_exact(&mut buf).await);
-        info!("read done, got {:[u8]}", buf);
-
-        // Reverse buf
-        for i in 0..4 {
-            let tmp = buf[i];
-            buf[i] = buf[7 - i];
-            buf[7 - i] = tmp;
-        }
-
-        info!("writing...");
-        unwrap!(u.write_all(&buf).await);
-        info!("write done");
-    }
-}
-
-static EXECUTOR: Forever<Executor> = Forever::new();
-
-#[entry]
-fn main() -> ! {
-    info!("Hello World!");
-
-    let executor = EXECUTOR.put(Executor::new(cortex_m::asm::sev));
-    unwrap!(executor.spawn(run()));
+    unwrap!(executor.spawn(run(uart)));
 
     loop {
         executor.run();