static void timer_setup(void) {
    rcc_periph_clock_enable(RCC_TIM3);

    timer_reset(TIM3);
    timer_set_mode(TIM3,            // Operate on TIM3
            TIM_CR1_CKD_CK_INT,     // No prescaling(Internal clock)
            TIM_CR1_CMS_EDGE,       // Edge-aligned
            TIM_CR1_DIR_UP);        // Up-counting

    timer_set_period(TIM3, 168);

    nvic_enable_irq(NVIC_TIM3_IRQ);
    timer_enable_irq(TIM3, TIM_DIER_CC1IE);

    timer_enable_counter(TIM3);
}