44 lines
1.3 KiB
Rust
44 lines
1.3 KiB
Rust
use core::cell::RefCell;
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use cortex_m::interrupt::Mutex;
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use cortex_m::peripheral::{SYST, syst::SystClkSource};
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use cortex_m_rt::exception;
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use bare_metal::CriticalSection;
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static mut TIME: Mutex<RefCell<u64>> = Mutex::new(RefCell::new(0));
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/// In HZ
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const RATE: u32 = 10;
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/// Period between two interrupts in ns
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const INTERVAL: u64 = 1_000_000 / RATE as u64;
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fn syst() -> &'static mut SYST {
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#[allow(mutable_transmutes)]
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unsafe { core::mem::transmute(&*SYST::ptr()) }
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}
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pub fn init(_cs: &CriticalSection) {
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let syst = syst();
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// syst.set_clock_source(SystClkSource::Core);
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syst.set_clock_source(SystClkSource::External);
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syst.set_reload(100 * SYST::get_ticks_per_10ms() / RATE);
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syst.clear_current();
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syst.enable_interrupt();
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syst.enable_counter();
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}
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#[exception]
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unsafe fn SysTick() {
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cortex_m::interrupt::free(|cs| {
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TIME.borrow(cs).replace_with(|time| *time + INTERVAL);
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});
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}
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pub fn get_time() -> u64 {
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let base = cortex_m::interrupt::free(|cs| {
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*unsafe { &mut TIME }.borrow(cs).borrow()
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});
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let syst_current = u64::from(SYST::get_current());
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let syst_reload = u64::from(SYST::get_reload());
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let precise = INTERVAL - (INTERVAL * syst_current / syst_reload);
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base + u64::from(precise)
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}
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