Add uart::Read DMA-based implementation

* Rename existing read() to bread() (blocking)

examples/stm32l0/src/bin/usart_dma.rs

@@ -0,0 +1,42 @@
+#![no_std]
+#![no_main]
+#![feature(trait_alias)]
+#![feature(min_type_alias_impl_trait)]
+#![feature(impl_trait_in_bindings)]
+#![feature(type_alias_impl_trait)]
+#![allow(incomplete_features)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+
+use example_common::*;
+
+use defmt::panic;
+use embassy::executor::Spawner;
+use embassy_stm32::usart::{Config, Uart};
+use embassy_stm32::{rcc, Peripherals};
+use embassy_traits::uart::{Read, Write};
+
+#[embassy::main]
+async fn main(_spawner: Spawner, mut p: Peripherals) {
+    let mut rcc = rcc::Rcc::new(p.RCC);
+    rcc.enable_debug_wfe(&mut p.DBGMCU, true);
+
+    let mut usart = Uart::new(
+        p.USART1,
+        p.PB7,
+        p.PB6,
+        p.DMA1_CH2,
+        p.DMA1_CH3,
+        Config::default(),
+    );
+
+    usart.write(b"Hello Embassy World!\r\n").await.unwrap();
+    info!("wrote Hello, starting echo");
+
+    let mut buf = [0; 1];
+    loop {
+        usart.read(&mut buf[..]).await.unwrap();
+        usart.write(&buf[..]).await.unwrap();
+    }
+}