bluepill-rust-blinky/src/main.rs

//! Blinks an LED
//!
//! This assumes that a LED is connected to pc13 as is the case on the blue pill board.
//!
//! Note: Without additional hardware, PC13 should not be used to drive an LED, see page 5.1.2 of
//! the reference manual for an explanation. This is not an issue on the blue pill.

#![deny(unsafe_code)]
#![no_std]
#![no_main]

use panic_halt as _;

use nb::block;

use cortex_m_rt::entry;
use stm32f1xx_hal::{pac, prelude::*, rcc::Config, timer::Timer};

#[entry]
fn main() -> ! {
    // Get access to the core peripherals from the cortex-m crate
    let cp = cortex_m::Peripherals::take().unwrap();
    // Get access to the device specific peripherals from the peripheral access crate
    let dp = pac::Peripherals::take().unwrap();

    // Take ownership over the raw flash and rcc devices and convert them into the corresponding
    // HAL structs
    let mut flash = dp.FLASH.constrain();
    let rcc = dp.RCC.constrain();

    // Freeze the configuration of all the clocks in the system and store the frozen frequencies in
    // `clocks`
    let clocks = rcc.cfgr.freeze_with_config(
        Config {
            // HSE frequency
            hse: Some(8_000_000),
            // PLLMUL represented by an integer -2
            pllmul: Some(9 - 2),
            // PCLK1 freq must be 36 MHz or less
            ppre1: stm32f1xx_hal::rcc::PPre::Div2,
            // ADCCLK freq must be 14 MHz or less
            adcpre: pac::rcc::cfgr::ADCPRE_A::Div6,
            ..Default::default()
        },
        &mut flash.acr,
    );

    // Acquire the GPIOC peripheral
    let mut gpioc = dp.GPIOC.split();

    // Configure gpio C pin 13 as a push-pull output. The `crh` register is passed to the function
    // in order to configure the port. For pins 0-7, crl should be passed instead.
    let mut led = gpioc.pc13.into_push_pull_output(&mut gpioc.crh);

    // Configure the syst timer to trigger an update every second
    let mut timer = Timer::syst(cp.SYST, &clocks).counter_hz();
    // at 72 MHz, timer of 1 Hz overflows, use 10 Hz instead (8 Hz experimental minimum)
    timer.start(10.Hz()).unwrap();

    // equivalent timers:
    // let mut timer = Timer::syst(cp.SYST, &clocks).counter_us(); // us resolution
    // let mut timer: SysCounter<1000> = Timer::syst(cp.SYST, &clocks).counter(); // ms resolution
    // timer.start(100.millis()).unwrap();

    // Wait for the timer to trigger an update and change the state of the LED
    loop {
        for _ in 0..10 {
            block!(timer.wait()).unwrap();
        }
        led.set_high();

        for _ in 0..10 {
            block!(timer.wait()).unwrap();
        }
        led.set_low();
    }
}