void timer_init(void)
{
TIM_TimeBaseInitTypeDef TIM4_init;
TIM_ICInitTypeDef timer_ic;
GPIO_InitTypeDef gpio_cfg;

RCC_AHB1PeriphClockCmd( RCC_AHB1Periph_GPIOD , ENABLE);

gpio_cfg.GPIO_Mode = GPIO_Mode_AF;
gpio_cfg.GPIO_Pin = GPIO_Pin_12;
GPIO_Init(GPIOD, &gpio_cfg);

GPIO_PinAFConfig(GPIOD, GPIO_Pin_12, GPIO_AF_TIM4);

TIM4_init.TIM_ClockDivision = TIM_CKD_DIV1;
TIM4_init.TIM_CounterMode = TIM_CounterMode_Up;
TIM4_init.TIM_Period = 10000;
TIM4_init.TIM_Prescaler = 8400 - 1;

TIM_TimeBaseInit(TIM4, &TIM4_init);

timer_ic.TIM_Channel = TIM_Channel_1;
timer_ic.TIM_ICPolarity = TIM_ICPolarity_Rising;
timer_ic.TIM_ICSelection = TIM_ICSelection_DirectTI;
timer_ic.TIM_ICPrescaler = TIM_ICPSC_DIV1;
timer_ic.TIM_ICFilter = 0;
TIM_ICInit(TIM4, &timer_ic);

TIM_ITConfig(TIM4, TIM_IT_CC1, ENABLE);

TIM_Cmd(TIM4, ENABLE);

NVIC_EnableIRQ(TIM4_IRQn);
}

void TIM4_IRQHandler(void)
{
if (TIM_GetITStatus(TIM4, TIM_IT_CC1) != RESET)
{
TIM_ClearITPendingBit(TIM4, TIM_IT_CC1);
}
}

GPIO_PinAFConfig(GPIOD, GPIO_Pin_12, GPIO_AF_TIM4);

gpio_cfg.GPIO_Mode = GPIO_Mode_AF;
gpio_cfg.GPIO_Pin = GPIO_Pin_12;
GPIO_Init(GPIOD, &gpio_cfg);