Add a stopwatch example

Signed-off-by: Daniel Egger <daniel@eggers-club.de>

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Added
+
+- Another example resembling a stop watch controlled via serial interface
+
 ### Fixed
 
 - Incorrect PLLSRC bits when using HSE

Cargo.toml

@@ -80,6 +80,10 @@ opt-level = "s"
 name = "blinky_timer_irq"
 required-features = ["stm32f072", "rt"]
 
+[[example]]
+name = "serial_stopwatch"
+required-features = ["stm32f072", "rt"]
+
 [[example]]
 name = "dac"
 required-features = ["stm32f072"]

examples/serial_stopwatch.rs

@@ -0,0 +1,121 @@
+#![no_main]
+#![no_std]
+
+use panic_halt as _;
+
+use stm32f0xx_hal as hal;
+
+use crate::hal::{
+    prelude::*,
+    serial::Serial,
+    stm32::{interrupt, Interrupt, Peripherals, TIM7},
+    timers::{Event, Timer},
+};
+use core::cell::RefCell;
+use core::fmt::Write as _;
+use core::ops::DerefMut;
+
+use cortex_m::{interrupt::Mutex, peripheral::Peripherals as c_m_Peripherals};
+use cortex_m_rt::entry;
+
+// Make timer interrupt registers globally available
+static GINT: Mutex<RefCell<Option<Timer<TIM7>>>> = Mutex::new(RefCell::new(None));
+
+#[derive(Copy, Clone)]
+struct Time {
+    seconds: u32,
+    millis: u16,
+}
+
+static TIME: Mutex<RefCell<Time>> = Mutex::new(RefCell::new(Time {
+    seconds: 0,
+    millis: 0,
+}));
+
+// Define an interupt handler, i.e. function to call when interrupt occurs. Here if our external
+// interrupt trips when the timer timed out
+#[interrupt]
+fn TIM7() {
+    cortex_m::interrupt::free(|cs| {
+        // Move LED pin here, leaving a None in its place
+        GINT.borrow(cs)
+            .borrow_mut()
+            .deref_mut()
+            .as_mut()
+            .unwrap()
+            .wait()
+            .ok();
+        let mut time = TIME.borrow(cs).borrow_mut();
+        time.millis += 1;
+        if time.millis == 1000 {
+            time.millis = 0;
+            time.seconds += 1;
+        }
+    });
+}
+
+#[entry]
+fn main() -> ! {
+    if let (Some(p), Some(cp)) = (Peripherals::take(), c_m_Peripherals::take()) {
+        let mut serial = cortex_m::interrupt::free(move |cs| {
+            let mut flash = p.FLASH;
+            let mut rcc = p.RCC.configure().sysclk(48.mhz()).freeze(&mut flash);
+
+            // Use USART2 with PA2 and PA3 as serial port
+            let gpioa = p.GPIOA.split(&mut rcc);
+            let tx = gpioa.pa2.into_alternate_af1(cs);
+            let rx = gpioa.pa3.into_alternate_af1(cs);
+
+            // Set up a timer expiring every millisecond
+            let mut timer = Timer::tim7(p.TIM7, 1000.hz(), &mut rcc);
+
+            // Generate an interrupt when the timer expires
+            timer.listen(Event::TimeOut);
+
+            // Move the timer into our global storage
+            *GINT.borrow(cs).borrow_mut() = Some(timer);
+
+            // Enable TIM7 IRQ, set prio 1 and clear any pending IRQs
+            let mut nvic = cp.NVIC;
+            unsafe {
+                nvic.set_priority(Interrupt::TIM7, 1);
+                cortex_m::peripheral::NVIC::unmask(Interrupt::TIM7);
+            }
+            cortex_m::peripheral::NVIC::unpend(Interrupt::TIM7);
+
+            // Set up our serial port
+            Serial::usart2(p.USART2, (tx, rx), 115_200.bps(), &mut rcc)
+        });
+
+        // Print a welcome message
+        writeln!(
+            serial,
+            "Welcome to the stop watch, hit any key to see the current value and 0 to reset\r",
+        )
+        .ok();
+
+        loop {
+            // Wait for reception of a single byte
+            let received = nb::block!(serial.read()).unwrap();
+
+            let time = cortex_m::interrupt::free(|cs| {
+                let mut time = TIME.borrow(cs).borrow_mut();
+
+                // If we received a 0, reset the time
+                if received == b'0' {
+                    time.millis = 0;
+                    time.seconds = 0;
+                }
+
+                *time
+            });
+
+            // Print the current time
+            writeln!(serial, "{}.{:03}s\r", time.seconds, time.millis).ok();
+        }
+    }
+
+    loop {
+        continue;
+    }
+}