Putting it all together

#![no_std]

extern crate aux9;

use aux9::tim6;

#[inline(never)]
fn delay(tim6: &tim6::RegisterBlock, ms: u16) {
    // Set the timer to go off in `ms` ticks
    // 1 tick = 1 ms
    tim6.arr.write(|w| w.arr().bits(ms));

    // CEN: Enable the counter
    tim6.cr1.modify(|_, w| w.cen().set_bit());

    // Wait until the alarm goes off (until the update event occurs)
    while !tim6.sr.read().uif().bit_is_set() {}

    // Clear the update event flag
    tim6.sr.modify(|_, w| w.uif().clear_bit());
}

fn main() {
    let (mut leds, rcc, tim6) = aux9::init();

    // Power on the TIM6 timer
    rcc.apb1enr.modify(|_, w| w.tim6en().set_bit());

    // OPM Select one pulse mode
    // CEN Keep the counter disabled for now
    tim6.cr1.write(|w| w.opm().clear_bit().cen().set_bit());

    // Configure the prescaler to have the counter operate at 1 KHz
    // APB1_CLOCK = 8 MHz
    // PSC = 7999
    // 8 MHz / (7999 + 1) = 1 KHz
    // The counter (CNT) will increase on every millisecond
    tim6.psc.write(|w| w.psc().bits(7_999));

    let ms = 50;
    loop {
        for curr in 0..8 {
            let next = (curr + 1) % 8;

            leds[next].on();
            delay(tim6, ms);
            leds[curr].off();
            delay(tim6, ms);
        }
    }
}