void led_init(void)
{
    TIM_OC_InitTypeDef sConfigOC;
    TIM_HandleTypeDef htim13;

    /*Configure GPIO pins : PF8 */
    __HAL_AFIO_REMAP_TIM13_ENABLE();
    __GPIOF_CLK_ENABLE();
    GPIO_InitStruct.Pin = GPIO_PIN_8;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
    HAL_GPIO_Init(GPIOF, &GPIO_InitStruct);

    htim13.Instance = TIM13;
    htim13.Init.Prescaler = (uint32_t)(72000000 / 2000000) - 1;
    htim13.Init.CounterMode = TIM_COUNTERMODE_UP;
    htim13.Init.Period = 700;
    htim13.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
    HAL_TIM_Base_Init(&htim13);

    HAL_TIM_PWM_Init(&htim13);

    sConfigOC.OCMode = TIM_OCMODE_PWM1;
    sConfigOC.Pulse = 350;
    sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
    sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
    sConfigOC.OCNPolarity  = TIM_OCNPOLARITY_HIGH;
    sConfigOC.OCNIdleState = TIM_OCNIDLESTATE_RESET;
    sConfigOC.OCIdleState  = TIM_OCIDLESTATE_RESET;

    HAL_TIM_PWM_ConfigChannel(&htim13, &sConfigOC, TIM_CHANNEL_1);
    HAL_TIM_PWM_Start(&htim13, TIM_CHANNEL_1);
}