atsamd_hal/
timer_params.rs

1//! helper struct to calculate divider & cycles settings for timers.
2use crate::time::{Hertz, Nanoseconds};
3
4/// Helper type for computing cycles and divider given frequency
5#[derive(Debug, Clone, Copy)]
6pub struct TimerParams {
7    pub divider: u16,
8    pub cycles: u32,
9}
10
11impl TimerParams {
12    /// Calculates the [`TimerParams`] from a given frequency based timeout.
13    ///
14    /// Panics if the combination of `timeout` and `src_freq` cannot be done
15    /// with a 16-bit timer.
16    pub fn new(timeout: Hertz, src_freq: Hertz) -> Self {
17        let ticks: u32 = src_freq.to_Hz() / timeout.to_Hz().max(1);
18        let ret = Self::new_from_ticks(ticks);
19        ret.check_cycles_u16();
20        ret
21    }
22
23    /// Calculates the [`TimerParams`] from a given period based timeout.
24    ///
25    /// Panics if the combination of `timeout` and `src_freq` cannot be done
26    /// with a 16-bit timer.
27    pub fn new_ns(timeout: Nanoseconds, src_freq: Hertz) -> Self {
28        let ticks: u32 =
29            (timeout.to_nanos() as u64 * src_freq.to_Hz() as u64 / 1_000_000_000_u64) as u32;
30        let ret = Self::new_from_ticks(ticks);
31        ret.check_cycles_u16();
32        ret
33    }
34
35    pub(crate) fn new_from_ticks(ticks: u32) -> Self {
36        let divider = ((ticks >> 16) + 1).next_power_of_two();
37        let divider = match divider {
38            1 | 2 | 4 | 8 | 16 | 64 | 256 | 1024 => divider,
39            // There are a couple of gaps, so we round up to the next largest
40            // divider; we'll need to count twice as many but it will work.
41            32 => 64,
42            128 => 256,
43            512 => 1024,
44            // Catch all case; this is lame.  Would be great to detect this
45            // and fail at compile time.
46            _ => 1024,
47        };
48
49        let cycles: u32 = ticks / divider;
50
51        TimerParams {
52            divider: divider as u16,
53            cycles,
54        }
55    }
56
57    /// Returns the number of required `cycles` as a `u16` and panics if the
58    /// number is too high to fit.
59    pub(crate) fn check_cycles_u16(&self) -> u16 {
60        match u16::try_from(self.cycles) {
61            Ok(c) => c,
62            Err(_) => panic!(
63                "cycles {} is out of range for a 16 bit counter",
64                self.cycles
65            ),
66        }
67    }
68}
69
70#[cfg(test)]
71mod tests {
72    use crate::fugit::{ExtU32, RateExtU32};
73    use crate::timer_params::TimerParams;
74
75    #[test]
76    fn timer_params_hz_and_us_same_1hz() {
77        let tp_from_hz = TimerParams::new(1.Hz(), 48.MHz());
78        let tp_from_us = TimerParams::new_ns(1_000_000.micros(), 48.MHz());
79
80        assert_eq!(tp_from_hz.divider, tp_from_us.divider);
81        assert_eq!(tp_from_hz.cycles, tp_from_us.cycles);
82    }
83
84    #[test]
85    fn timer_params_hz_and_us_same_3hz() {
86        let tp_from_hz = TimerParams::new(3.Hz(), 48.MHz());
87        let tp_from_us = TimerParams::new_ns(333_333.micros(), 48.MHz());
88
89        // There's some rounding error here, but it is extremely small (1 cycle
90        // difference)
91        assert_eq!(tp_from_hz.divider, tp_from_us.divider);
92        assert!((tp_from_hz.cycles as i32 - tp_from_us.cycles as i32).abs() <= 1);
93    }
94}
atsamd_hal/timer_params.rs

atsamd_hal/
timer_params.rs
