Merge #934

934: (embassy-rp): Add Buffered UART implementation r=MathiasKoch a=MathiasKoch

### Questions & concerns: 
- ~~Would it make sense to add `RxBufferedUart` and `TxBufferedUart`, for cases where you would want to only buffer one way?~~
- ~~Do I need to be monitoring more interrupt flags than `Receive` & `Receive timeout`?~~

This PR adds working `BufferedUart` implementation, along with `RxBufferedUart` and `TxBufferedUart`. The implementation leaves room for improvement with respect to performance, as it still does not utilize DMA nor the internal UART buffers.

Co-authored-by: Mathias <mk@blackbird.online>
Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>

embassy-rp/Cargo.toml

@@ -27,7 +27,7 @@ intrinsics = []
 rom-v2-intrinsics = []
 
 # Enable nightly-only features
-nightly = ["embassy-executor/nightly", "embedded-hal-1", "embedded-hal-async", "embassy-embedded-hal/nightly", "dep:embassy-usb"]
+nightly = ["embassy-executor/nightly", "embedded-hal-1", "embedded-hal-async", "embassy-embedded-hal/nightly", "dep:embassy-usb", "dep:embedded-io"]
 
 # Implement embedded-hal 1.0 alpha traits.
 # Implement embedded-hal-async traits if `nightly` is set as well.
@@ -52,6 +52,7 @@ cortex-m = "0.7.6"
 critical-section = "1.1"
 futures = { version = "0.3.17", default-features = false, features = ["async-await"] }
 chrono = { version = "0.4", default-features = false, optional = true }
+embedded-io = { version = "0.3.0", features = ["async"], optional = true }
 
 rp2040-pac2 = { git = "https://github.com/embassy-rs/rp2040-pac2", rev="017e3c9007b2d3b6965f0d85b5bf8ce3fa6d7364", features = ["rt"] }
 #rp2040-pac2 = { path = "../../rp2040-pac2", features = ["rt"] }

embassy-rp/src/uart/buffered.rs

@@ -0,0 +1,489 @@
+use core::future::{poll_fn, Future};
+use core::task::{Poll, Waker};
+
+use atomic_polyfill::{compiler_fence, Ordering};
+use embassy_cortex_m::peripheral::{PeripheralMutex, PeripheralState, StateStorage};
+use embassy_hal_common::ring_buffer::RingBuffer;
+use embassy_sync::waitqueue::WakerRegistration;
+
+use super::*;
+
+pub struct State<'d, T: Instance>(StateStorage<FullStateInner<'d, T>>);
+impl<'d, T: Instance> State<'d, T> {
+    pub const fn new() -> Self {
+        Self(StateStorage::new())
+    }
+}
+
+pub struct RxState<'d, T: Instance>(StateStorage<RxStateInner<'d, T>>);
+impl<'d, T: Instance> RxState<'d, T> {
+    pub const fn new() -> Self {
+        Self(StateStorage::new())
+    }
+}
+
+pub struct TxState<'d, T: Instance>(StateStorage<TxStateInner<'d, T>>);
+impl<'d, T: Instance> TxState<'d, T> {
+    pub const fn new() -> Self {
+        Self(StateStorage::new())
+    }
+}
+
+struct RxStateInner<'d, T: Instance> {
+    phantom: PhantomData<&'d mut T>,
+
+    waker: WakerRegistration,
+    buf: RingBuffer<'d>,
+}
+
+struct TxStateInner<'d, T: Instance> {
+    phantom: PhantomData<&'d mut T>,
+
+    waker: WakerRegistration,
+    buf: RingBuffer<'d>,
+}
+
+struct FullStateInner<'d, T: Instance> {
+    rx: RxStateInner<'d, T>,
+    tx: TxStateInner<'d, T>,
+}
+
+unsafe impl<'d, T: Instance> Send for RxStateInner<'d, T> {}
+unsafe impl<'d, T: Instance> Sync for RxStateInner<'d, T> {}
+
+unsafe impl<'d, T: Instance> Send for TxStateInner<'d, T> {}
+unsafe impl<'d, T: Instance> Sync for TxStateInner<'d, T> {}
+
+unsafe impl<'d, T: Instance> Send for FullStateInner<'d, T> {}
+unsafe impl<'d, T: Instance> Sync for FullStateInner<'d, T> {}
+
+pub struct BufferedUart<'d, T: Instance> {
+    inner: PeripheralMutex<'d, FullStateInner<'d, T>>,
+}
+
+pub struct BufferedUartRx<'d, T: Instance> {
+    inner: PeripheralMutex<'d, RxStateInner<'d, T>>,
+}
+
+pub struct BufferedUartTx<'d, T: Instance> {
+    inner: PeripheralMutex<'d, TxStateInner<'d, T>>,
+}
+
+impl<'d, T: Instance> Unpin for BufferedUart<'d, T> {}
+impl<'d, T: Instance> Unpin for BufferedUartRx<'d, T> {}
+impl<'d, T: Instance> Unpin for BufferedUartTx<'d, T> {}
+
+impl<'d, T: Instance> BufferedUart<'d, T> {
+    pub fn new<M: Mode>(
+        state: &'d mut State<'d, T>,
+        _uart: Uart<'d, T, M>,
+        irq: impl Peripheral<P = T::Interrupt> + 'd,
+        tx_buffer: &'d mut [u8],
+        rx_buffer: &'d mut [u8],
+    ) -> BufferedUart<'d, T> {
+        into_ref!(irq);
+
+        let r = T::regs();
+        unsafe {
+            r.uartimsc().modify(|w| {
+                w.set_rxim(true);
+                w.set_rtim(true);
+                w.set_txim(true);
+            });
+        }
+
+        Self {
+            inner: PeripheralMutex::new(irq, &mut state.0, move || FullStateInner {
+                tx: TxStateInner {
+                    phantom: PhantomData,
+                    waker: WakerRegistration::new(),
+                    buf: RingBuffer::new(tx_buffer),
+                },
+                rx: RxStateInner {
+                    phantom: PhantomData,
+                    waker: WakerRegistration::new(),
+                    buf: RingBuffer::new(rx_buffer),
+                },
+            }),
+        }
+    }
+}
+
+impl<'d, T: Instance> BufferedUartRx<'d, T> {
+    pub fn new<M: Mode>(
+        state: &'d mut RxState<'d, T>,
+        _uart: UartRx<'d, T, M>,
+        irq: impl Peripheral<P = T::Interrupt> + 'd,
+        rx_buffer: &'d mut [u8],
+    ) -> BufferedUartRx<'d, T> {
+        into_ref!(irq);
+
+        let r = T::regs();
+        unsafe {
+            r.uartimsc().modify(|w| {
+                w.set_rxim(true);
+                w.set_rtim(true);
+            });
+        }
+
+        Self {
+            inner: PeripheralMutex::new(irq, &mut state.0, move || RxStateInner {
+                phantom: PhantomData,
+
+                buf: RingBuffer::new(rx_buffer),
+                waker: WakerRegistration::new(),
+            }),
+        }
+    }
+}
+
+impl<'d, T: Instance> BufferedUartTx<'d, T> {
+    pub fn new<M: Mode>(
+        state: &'d mut TxState<'d, T>,
+        _uart: UartTx<'d, T, M>,
+        irq: impl Peripheral<P = T::Interrupt> + 'd,
+        tx_buffer: &'d mut [u8],
+    ) -> BufferedUartTx<'d, T> {
+        into_ref!(irq);
+
+        let r = T::regs();
+        unsafe {
+            r.uartimsc().modify(|w| {
+                w.set_txim(true);
+            });
+        }
+
+        Self {
+            inner: PeripheralMutex::new(irq, &mut state.0, move || TxStateInner {
+                phantom: PhantomData,
+
+                buf: RingBuffer::new(tx_buffer),
+                waker: WakerRegistration::new(),
+            }),
+        }
+    }
+}
+
+impl<'d, T: Instance> PeripheralState for FullStateInner<'d, T>
+where
+    Self: 'd,
+{
+    type Interrupt = T::Interrupt;
+    fn on_interrupt(&mut self) {
+        self.rx.on_interrupt();
+        self.tx.on_interrupt();
+    }
+}
+
+impl<'d, T: Instance> RxStateInner<'d, T>
+where
+    Self: 'd,
+{
+    fn read(&mut self, buf: &mut [u8], waker: &Waker) -> (Poll<Result<usize, Error>>, bool) {
+        // We have data ready in buffer? Return it.
+        let mut do_pend = false;
+        let data = self.buf.pop_buf();
+        if !data.is_empty() {
+            let len = data.len().min(buf.len());
+            buf[..len].copy_from_slice(&data[..len]);
+
+            if self.buf.is_full() {
+                do_pend = true;
+            }
+            self.buf.pop(len);
+
+            return (Poll::Ready(Ok(len)), do_pend);
+        }
+
+        self.waker.register(waker);
+        (Poll::Pending, do_pend)
+    }
+
+    fn fill_buf<'a>(&mut self, waker: &Waker) -> Poll<Result<&'a [u8], Error>> {
+        // We have data ready in buffer? Return it.
+        let buf = self.buf.pop_buf();
+        if !buf.is_empty() {
+            let buf: &[u8] = buf;
+            // Safety: buffer lives as long as uart
+            let buf: &[u8] = unsafe { core::mem::transmute(buf) };
+            return Poll::Ready(Ok(buf));
+        }
+
+        self.waker.register(waker);
+        Poll::Pending
+    }
+
+    fn consume(&mut self, amt: usize) -> bool {
+        let full = self.buf.is_full();
+        self.buf.pop(amt);
+        full
+    }
+}
+
+impl<'d, T: Instance> PeripheralState for RxStateInner<'d, T>
+where
+    Self: 'd,
+{
+    type Interrupt = T::Interrupt;
+    fn on_interrupt(&mut self) {
+        let r = T::regs();
+        unsafe {
+            let ris = r.uartris().read();
+            // Clear interrupt flags
+            r.uarticr().modify(|w| {
+                w.set_rxic(true);
+                w.set_rtic(true);
+            });
+
+            if ris.peris() {
+                warn!("Parity error");
+                r.uarticr().modify(|w| {
+                    w.set_peic(true);
+                });
+            }
+            if ris.feris() {
+                warn!("Framing error");
+                r.uarticr().modify(|w| {
+                    w.set_feic(true);
+                });
+            }
+            if ris.beris() {
+                warn!("Break error");
+                r.uarticr().modify(|w| {
+                    w.set_beic(true);
+                });
+            }
+            if ris.oeris() {
+                warn!("Overrun error");
+                r.uarticr().modify(|w| {
+                    w.set_oeic(true);
+                });
+            }
+
+            if !r.uartfr().read().rxfe() {
+                let buf = self.buf.push_buf();
+                if !buf.is_empty() {
+                    buf[0] = r.uartdr().read().data();
+                    self.buf.push(1);
+                } else {
+                    warn!("RX buffer full, discard received byte");
+                }
+
+                if self.buf.is_full() {
+                    self.waker.wake();
+                }
+            }
+
+            if ris.rtris() {
+                self.waker.wake();
+            };
+        }
+    }
+}
+
+impl<'d, T: Instance> TxStateInner<'d, T>
+where
+    Self: 'd,
+{
+    fn write(&mut self, buf: &[u8], waker: &Waker) -> (Poll<Result<usize, Error>>, bool) {
+        let empty = self.buf.is_empty();
+        let tx_buf = self.buf.push_buf();
+        if tx_buf.is_empty() {
+            self.waker.register(waker);
+            return (Poll::Pending, empty);
+        }
+
+        let n = core::cmp::min(tx_buf.len(), buf.len());
+        tx_buf[..n].copy_from_slice(&buf[..n]);
+        self.buf.push(n);
+
+        (Poll::Ready(Ok(n)), empty)
+    }
+
+    fn flush(&mut self, waker: &Waker) -> Poll<Result<(), Error>> {
+        if !self.buf.is_empty() {
+            self.waker.register(waker);
+            return Poll::Pending;
+        }
+
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<'d, T: Instance> PeripheralState for TxStateInner<'d, T>
+where
+    Self: 'd,
+{
+    type Interrupt = T::Interrupt;
+    fn on_interrupt(&mut self) {
+        let r = T::regs();
+        unsafe {
+            let buf = self.buf.pop_buf();
+            if !buf.is_empty() {
+                r.uartimsc().modify(|w| {
+                    w.set_txim(true);
+                });
+                r.uartdr().write(|w| w.set_data(buf[0].into()));
+                self.buf.pop(1);
+                self.waker.wake();
+            } else {
+                // Disable interrupt until we have something to transmit again
+                r.uartimsc().modify(|w| {
+                    w.set_txim(false);
+                });
+            }
+        }
+    }
+}
+
+impl embedded_io::Error for Error {
+    fn kind(&self) -> embedded_io::ErrorKind {
+        embedded_io::ErrorKind::Other
+    }
+}
+
+impl<'d, T: Instance> embedded_io::Io for BufferedUart<'d, T> {
+    type Error = Error;
+}
+
+impl<'d, T: Instance> embedded_io::Io for BufferedUartRx<'d, T> {
+    type Error = Error;
+}
+
+impl<'d, T: Instance> embedded_io::Io for BufferedUartTx<'d, T> {
+    type Error = Error;
+}
+
+impl<'d, T: Instance + 'd> embedded_io::asynch::Read for BufferedUart<'d, T> {
+    type ReadFuture<'a> = impl Future<Output = Result<usize, Self::Error>>
+    where
+        Self: 'a;
+
+    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Self::ReadFuture<'a> {
+        poll_fn(move |cx| {
+            let (res, do_pend) = self.inner.with(|state| {
+                compiler_fence(Ordering::SeqCst);
+                state.rx.read(buf, cx.waker())
+            });
+
+            if do_pend {
+                self.inner.pend();
+            }
+
+            res
+        })
+    }
+}
+
+impl<'d, T: Instance + 'd> embedded_io::asynch::Read for BufferedUartRx<'d, T> {
+    type ReadFuture<'a> = impl Future<Output = Result<usize, Self::Error>>
+    where
+        Self: 'a;
+
+    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Self::ReadFuture<'a> {
+        poll_fn(move |cx| {
+            let (res, do_pend) = self.inner.with(|state| {
+                compiler_fence(Ordering::SeqCst);
+                state.read(buf, cx.waker())
+            });
+
+            if do_pend {
+                self.inner.pend();
+            }
+
+            res
+        })
+    }
+}
+
+impl<'d, T: Instance + 'd> embedded_io::asynch::BufRead for BufferedUart<'d, T> {
+    type FillBufFuture<'a> = impl Future<Output = Result<&'a [u8], Self::Error>>
+    where
+        Self: 'a;
+
+    fn fill_buf<'a>(&'a mut self) -> Self::FillBufFuture<'a> {
+        poll_fn(move |cx| {
+            self.inner.with(|state| {
+                compiler_fence(Ordering::SeqCst);
+                state.rx.fill_buf(cx.waker())
+            })
+        })
+    }
+
+    fn consume(&mut self, amt: usize) {
+        let signal = self.inner.with(|state| state.rx.consume(amt));
+        if signal {
+            self.inner.pend();
+        }
+    }
+}
+
+impl<'d, T: Instance + 'd> embedded_io::asynch::BufRead for BufferedUartRx<'d, T> {
+    type FillBufFuture<'a> = impl Future<Output = Result<&'a [u8], Self::Error>>
+    where
+        Self: 'a;
+
+    fn fill_buf<'a>(&'a mut self) -> Self::FillBufFuture<'a> {
+        poll_fn(move |cx| {
+            self.inner.with(|state| {
+                compiler_fence(Ordering::SeqCst);
+                state.fill_buf(cx.waker())
+            })
+        })
+    }
+
+    fn consume(&mut self, amt: usize) {
+        let signal = self.inner.with(|state| state.consume(amt));
+        if signal {
+            self.inner.pend();
+        }
+    }
+}
+
+impl<'d, T: Instance + 'd> embedded_io::asynch::Write for BufferedUart<'d, T> {
+    type WriteFuture<'a> = impl Future<Output = Result<usize, Self::Error>>
+    where
+        Self: 'a;
+
+    fn write<'a>(&'a mut self, buf: &'a [u8]) -> Self::WriteFuture<'a> {
+        poll_fn(move |cx| {
+            let (poll, empty) = self.inner.with(|state| state.tx.write(buf, cx.waker()));
+            if empty {
+                self.inner.pend();
+            }
+            poll
+        })
+    }
+
+    type FlushFuture<'a> = impl Future<Output = Result<(), Self::Error>>
+    where
+        Self: 'a;
+
+    fn flush<'a>(&'a mut self) -> Self::FlushFuture<'a> {
+        poll_fn(move |cx| self.inner.with(|state| state.tx.flush(cx.waker())))
+    }
+}
+
+impl<'d, T: Instance + 'd> embedded_io::asynch::Write for BufferedUartTx<'d, T> {
+    type WriteFuture<'a> = impl Future<Output = Result<usize, Self::Error>>
+    where
+        Self: 'a;
+
+    fn write<'a>(&'a mut self, buf: &'a [u8]) -> Self::WriteFuture<'a> {
+        poll_fn(move |cx| {
+            let (poll, empty) = self.inner.with(|state| state.write(buf, cx.waker()));
+            if empty {
+                self.inner.pend();
+            }
+            poll
+        })
+    }
+
+    type FlushFuture<'a> = impl Future<Output = Result<(), Self::Error>>
+    where
+        Self: 'a;
+
+    fn flush<'a>(&'a mut self) -> Self::FlushFuture<'a> {
+        poll_fn(move |cx| self.inner.with(|state| state.flush(cx.waker())))
+    }
+}

embassy-rp/src/uart/mod.rs

@@ -346,6 +346,11 @@ impl<'d, T: Instance, M: Mode> Uart<'d, T, M> {
                 w.set_fen(true);
             });
 
+            r.uartifls().write(|w| {
+                w.set_rxiflsel(0b000);
+                w.set_txiflsel(0b000);
+            });
+
             r.uartcr().write(|w| {
                 w.set_uarten(true);
                 w.set_rxe(true);
@@ -475,6 +480,75 @@ mod eh1 {
     impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::ErrorType for UartRx<'d, T, M> {
         type Error = Error;
     }
+
+    impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::nb::Read for UartRx<'d, T, M> {
+        fn read(&mut self) -> nb::Result<u8, Self::Error> {
+            let r = T::regs();
+            unsafe {
+                let dr = r.uartdr().read();
+
+                if dr.oe() {
+                    Err(nb::Error::Other(Error::Overrun))
+                } else if dr.be() {
+                    Err(nb::Error::Other(Error::Break))
+                } else if dr.pe() {
+                    Err(nb::Error::Other(Error::Parity))
+                } else if dr.fe() {
+                    Err(nb::Error::Other(Error::Framing))
+                } else if dr.fe() {
+                    Ok(dr.data())
+                } else {
+                    Err(nb::Error::WouldBlock)
+                }
+            }
+        }
+    }
+
+    impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::blocking::Write for UartTx<'d, T, M> {
+        fn write(&mut self, buffer: &[u8]) -> Result<(), Self::Error> {
+            self.blocking_write(buffer)
+        }
+
+        fn flush(&mut self) -> Result<(), Self::Error> {
+            self.blocking_flush()
+        }
+    }
+
+    impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::nb::Write for UartTx<'d, T, M> {
+        fn write(&mut self, char: u8) -> nb::Result<(), Self::Error> {
+            self.blocking_write(&[char]).map_err(nb::Error::Other)
+        }
+
+        fn flush(&mut self) -> nb::Result<(), Self::Error> {
+            self.blocking_flush().map_err(nb::Error::Other)
+        }
+    }
+
+    impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::nb::Read for Uart<'d, T, M> {
+        fn read(&mut self) -> Result<u8, nb::Error<Self::Error>> {
+            embedded_hal_02::serial::Read::read(&mut self.rx)
+        }
+    }
+
+    impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::blocking::Write for Uart<'d, T, M> {
+        fn write(&mut self, buffer: &[u8]) -> Result<(), Self::Error> {
+            self.blocking_write(buffer)
+        }
+
+        fn flush(&mut self) -> Result<(), Self::Error> {
+            self.blocking_flush()
+        }
+    }
+
+    impl<'d, T: Instance, M: Mode> embedded_hal_1::serial::nb::Write for Uart<'d, T, M> {
+        fn write(&mut self, char: u8) -> nb::Result<(), Self::Error> {
+            self.blocking_write(&[char]).map_err(nb::Error::Other)
+        }
+
+        fn flush(&mut self) -> nb::Result<(), Self::Error> {
+            self.blocking_flush().map_err(nb::Error::Other)
+        }
+    }
 }
 
 #[cfg(all(
@@ -532,6 +606,11 @@ mod eha {
     }
 }
 
+#[cfg(feature = "nightly")]
+mod buffered;
+#[cfg(feature = "nightly")]
+pub use buffered::*;
+
 mod sealed {
     use super::*;
 
@@ -541,6 +620,8 @@ mod sealed {
         const TX_DREQ: u8;
         const RX_DREQ: u8;
 
+        type Interrupt: crate::interrupt::Interrupt;
+
         fn regs() -> pac::uart::Uart;
     }
     pub trait TxPin<T: Instance> {}
@@ -572,6 +653,8 @@ macro_rules! impl_instance {
             const TX_DREQ: u8 = $tx_dreq;
             const RX_DREQ: u8 = $rx_dreq;
 
+            type Interrupt = crate::interrupt::$irq;
+
             fn regs() -> pac::uart::Uart {
                 pac::$inst
             }
@@ -580,8 +663,8 @@ macro_rules! impl_instance {
     };
 }
 
-impl_instance!(UART0, UART0, 20, 21);
-impl_instance!(UART1, UART1, 22, 23);
+impl_instance!(UART0, UART0_IRQ, 20, 21);
+impl_instance!(UART1, UART1_IRQ, 22, 23);
 
 pub trait TxPin<T: Instance>: sealed::TxPin<T> + crate::gpio::Pin {}
 pub trait RxPin<T: Instance>: sealed::RxPin<T> + crate::gpio::Pin {}

tests/rp/.cargo/config.toml

@@ -3,7 +3,7 @@ build-std = ["core"]
 build-std-features = ["panic_immediate_abort"]
 
 [target.'cfg(all(target_arch = "arm", target_os = "none"))']
-#runner = "teleprobe client run --target bluepill-stm32f103c8 --elf"
+#runner = "teleprobe client run --target rpi-pico --elf"
 runner = "teleprobe local run --chip RP2040 --elf"
 
 rustflags = [

tests/rp/Cargo.toml

@@ -20,6 +20,7 @@ embedded-hal-1 = { package = "embedded-hal", version = "1.0.0-alpha.8" }
 embedded-hal-async = { version = "0.1.0-alpha.1" }
 panic-probe = { version = "0.3.0", features = ["print-defmt"] }
 futures = { version = "0.3.17", default-features = false, features = ["async-await"] }
+embedded-io = { version = "0.3.0", features = ["async"] }
 
 [profile.dev]
 debug = 2

tests/rp/src/bin/uart_buffered.rs

@@ -0,0 +1,44 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use defmt::{assert_eq, *};
+use embassy_executor::Spawner;
+use embassy_rp::interrupt;
+use embassy_rp::uart::{BufferedUart, Config, State, Uart};
+use embedded_io::asynch::{Read, Write};
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_rp::init(Default::default());
+    info!("Hello World!");
+
+    let (tx, rx, uart) = (p.PIN_0, p.PIN_1, p.UART0);
+
+    let config = Config::default();
+    let uart = Uart::new_blocking(uart, tx, rx, config);
+
+    let irq = interrupt::take!(UART0_IRQ);
+    let tx_buf = &mut [0u8; 16];
+    let rx_buf = &mut [0u8; 16];
+    let mut state = State::new();
+    let mut uart = BufferedUart::new(&mut state, uart, irq, tx_buf, rx_buf);
+
+    // Make sure we send more bytes than fits in the FIFO, to test the actual
+    // bufferedUart.
+
+    let data = [
+        1_u8, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
+        30, 31, 32,
+    ];
+    uart.write_all(&data).await.unwrap();
+    info!("Done writing");
+
+    let mut buf = [0; 32];
+    uart.read_exact(&mut buf).await.unwrap();
+    assert_eq!(buf, data);
+
+    info!("Test OK");
+    cortex_m::asm::bkpt();
+}