thermostat/src/timer.rs

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use core::cell::RefCell;
use core::ops::Deref;
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use cortex_m::interrupt::Mutex;
use cortex_m_rt::exception;
use stm32f4xx_hal::{
rcc::Clocks,
time::U32Ext,
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timer::{Timer, Event as TimerEvent},
stm32::SYST,
};
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/// Rate in Hz
const TIMER_RATE: u32 = 500;
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/// Interval duration in milliseconds
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const TIMER_DELTA: u32 = 1000 / TIMER_RATE;
/// Elapsed time in milliseconds
static TIMER_MS: Mutex<RefCell<u32>> = Mutex::new(RefCell::new(0));
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/// Setup SysTick exception
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pub fn setup(syst: SYST, clocks: Clocks) {
let mut timer = Timer::syst(syst, TIMER_RATE.hz(), clocks);
timer.listen(TimerEvent::TimeOut);
}
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/// SysTick exception (Timer)
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#[exception]
fn SysTick() {
cortex_m::interrupt::free(|cs| {
*TIMER_MS.borrow(cs)
.borrow_mut() += TIMER_DELTA;
});
}
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/// Obtain current time in milliseconds
pub fn now() -> u32 {
cortex_m::interrupt::free(|cs| {
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*TIMER_MS.borrow(cs)
.borrow()
.deref()
})
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}