added forgotten 07-uart source code

mdbook/src/07-uart/src/main.rs

@@ -0,0 +1,51 @@
+#![no_main]
+#![no_std]
+
+use cortex_m_rt::entry;
+use core::fmt::Write;
+use heapless::Vec;
+use microbit::hal::uarte::{self, Baudrate, Parity};
+use panic_rtt_target as _;
+use rtt_target::rtt_init_print;
+use serial_setup::UartePort;
+
+#[entry]
+fn main() -> ! {
+    rtt_init_print!();
+    let board = microbit::Board::take().unwrap();
+
+    let mut serial = {
+        let serial = uarte::Uarte::new(
+            board.UARTE0,
+            board.uart.into(),
+            Parity::EXCLUDED,
+            Baudrate::BAUD115200,
+        );
+        UartePort::new(serial)
+    };
+
+    // A buffer with 32 bytes of capacity
+    let mut buffer: Vec<u8, 32> = Vec::new();
+
+    loop {
+        buffer.clear();
+
+        loop {
+            // We assume that the receiving cannot fail
+            let byte = serial.read().unwrap();
+
+            if buffer.push(byte).is_err() {
+                write!(serial, "error: buffer full\r\n").unwrap();
+                break;
+            }
+
+            if byte == b'\r' {
+                for byte in buffer.iter().rev().chain(&[b'\n', b'\r']) {
+                    serial.write(*byte).unwrap();
+                }
+                break;
+            }
+        }
+        serial.flush().unwrap()
+    }
+}