Adding docs for the cycle counter

This commit is contained in:
Ryan Summers 2021-02-17 17:26:54 +01:00
parent 3c8cd58d6f
commit e8c4829790
1 changed files with 28 additions and 0 deletions

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@ -2,13 +2,29 @@ use rtic::cyccnt::{Duration, Instant, U32Ext};
use stm32h7xx_hal::time::Hertz;
/// A simple clock for counting elapsed milliseconds.
pub struct CycleCounter {
// The time of the next millisecond in the system.
next_tick: Option<Instant>,
// The number of elapsed milliseconds recorded.
ticks: u32,
// The increment amount of clock cycles for each elapsed millisecond.
increment: Duration,
}
impl CycleCounter {
/// Construct the cycle counting clock.
///
/// # Args
/// * `dwt` - The debug watch and trace unit of the CPU core.
/// * `cpu_frequency` - The frequency that the cycle counter counts at.
///
/// # Returns
/// A clock that can be used for measuring elapsed milliseconds.
pub fn new(
mut dwt: cortex_m::peripheral::DWT,
cpu_frequency: impl Into<Hertz>,
@ -24,6 +40,18 @@ impl CycleCounter {
}
}
/// Get the current number of milliseconds elapsed in the system.
///
/// # Note
/// This function must be called more often than once per 10 seconds to prevent internal
/// wrapping of the cycle counter.
///
/// The internal millisecond accumulator will overflow just shy of every 50 days.
///
/// This function does not start counting milliseconds until the very first invocation.
///
/// # Returns
/// The number of elapsed milliseconds since the system started.
pub fn current_ms(&mut self) -> u32 {
if self.next_tick.is_none() {
self.next_tick = Some(Instant::now() + self.increment);