[2/3] Timer abstraction: add OneShotTimer/PeriodicTimer drivers, Timer trait

[jessebraham]

This is still a bit messy overall, but I plan to clean things up in the next and final PR in this series. Refactoring and documentation will be improved in said PR.

At this time OneShotTimer is working correctly both when backed by TIMGx and SYSTIMER. PeriodicTimer is working when backed by TIMGx, however there is one small issue remaining when backed by SYSTIMER.

Given the following example:

#![no_std]
#![no_main]

use esp_backtrace as _;
use esp_hal::{
    peripherals::Peripherals,
    prelude::*,
    timer::{systimer::SystemTimer, PeriodicTimer},
};
use esp_println::println;

#[entry]
fn main() -> ! {
    let peripherals = Peripherals::take();

    let systimer = SystemTimer::new(peripherals.SYSTIMER);
    let mut periodic = PeriodicTimer::new(systimer.alarm0);

    println!("Countdown 5 times using PeriodicTimer...");
    periodic.start(1000.millis());
    let mut i = 5;
    while i > 0 {
        println!("{i}");
        nb::block!(periodic.wait()).unwrap();
        i -= 1;
    }
    periodic.cancel().unwrap();
    println!("Done!");

    loop {}
}

Both 5 and 4 are immediately printed, and then the countdown continues as expected from there. Not sure why the first iteration is clearing right away, still looking into it.

[bjoernQ]

Solution to the systimer periodic timer problem seems to be this:

i.e. this seems to fix it for me (tested on C6 only for now)

    fn load_value(&self, value: MicrosDurationU64) {
        ....

        if auto_reload {
            // Period mode

            systimer
                .target_conf(CHANNEL as usize)
                .modify(|_, w| unsafe { w.period().bits(ticks as u32) });

            #[cfg(not(esp32s2))]
            systimer
                .comp_load(CHANNEL as usize)
                .write(|w| w.load().set_bit());

            // Clear and then set SYSTIMER_TARGETx_PERIOD_MODE to configure COMPx into period mode
            systimer.target_conf(CHANNEL as usize).modify(|_,w| w.period_mode().clear_bit());
            systimer.target_conf(CHANNEL as usize).modify(|_,w| w.period_mode().set_bit());
        } else {
            // Target mode

                     .....

5 is still printed immediately but not 4

[MabezDev]

LGTM, thanks!

[bjoernQ]

LGTM - Thanks!