// Define the timer registers
#define TimerAlarm OCR3B
#define TimerCounter TCNT3

NVIC_InitTypeDef NVIC_InitStructure;
TIM_TimeBaseInitTypeDef TIM_InitStructure;
#define TIM2_IRQChannel ((u8)0x1C) /* TIM2 global Interrupt (alte Bibliothek)*/

#define TimerAlarm TIM2->CCMR1
#define TimerCounter TIM_GetCounter(TIM2)

#define TIMER_INTERRUPT_LEVEL 1

void timer_can_irq_handler(void);


/************************** Modul variables **********************************/
// Store the last timer value to calculate the elapsed time
static TIMEVAL last_time_set = TIMEVAL_MAX;

void initTimer(void)
/******************************************************************************
Initializes the timer, turn on the interrupt and put the interrupt time to zero
INPUT void
OUTPUT void
******************************************************************************/
{
//TODO: check
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); //TIM2 mit einem Takt versorgen

NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQChannel; //Interrupt Kanal auswählen. Hier TIM2
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1; //Interrupt Priorität festlegen
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; //Interrupt Unterpriorität festlegen
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //Aktivieren des Interrupts
NVIC_Init(&NVIC_InitStructure); //Konfiguration übernehmen

TIM_InitStructure.TIM_Prescaler = 2000; // Clock Teiler 72MHz / 2000 = 36kHz
TIM_InitStructure.TIM_Period = 36000; // Anzahl Durchläufe bis Überlauf Interrupt 36kHz / 36000 = 1s
TIM_InitStructure.TIM_ClockDivision = TIM_CKD_DIV1; //Keine Clock Division
TIM_InitStructure.TIM_CounterMode = TIM_CounterMode_Up; //Hochzählender Timer Modus
TIM_TimeBaseInit(TIM2, &TIM_InitStructure); //Konfiguration Übernehmen
TIM_Cmd(TIM2, ENABLE); //Timer Aktivieren

TIM_ClearFlag(TIM2, TIM_FLAG_Update); //Interrupt Flag von TIM2 löschen
TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE); //Interrupt für TIM2 Aktivieren
TIM_ClearFlag(TIM2, TIM_FLAG_Update); //Interrupt Flag für TIM2 Löschen
//End check


}

void setTimer(TIMEVAL value)
/******************************************************************************
Set the timer for the next alarm.
INPUT value TIMEVAL (unsigned long)
OUTPUT void
******************************************************************************/
{
TimerAlarm += value; // Add the desired time to timer interrupt time
}

TIMEVAL getElapsedTime(void)
/******************************************************************************
Return the elapsed time to tell the stack how much time is spent since last call.
INPUT void
OUTPUT value TIMEVAL (unsigned long) the elapsed time
******************************************************************************/
{
unsigned int timer = TimerCounter; // Copy the value of the running timer
// Calculate the time difference
return timer > last_time_set ? timer - last_time_set : last_time_set - timer;
}


//*----------------------------------------------------------------------------
//* Function Name : timer_can_irq_handler
//* Object : C handler interrupt function by the interrupts
//* assembling routine
//* Output Parameters : calls TimeDispatch
//*----------------------------------------------------------------------------
//void timer_can_irq_handler(void)
void TIM2_IRQHandler(void)
{
last_time_set = TimerCounter;
TimeDispatch(); // Call the time handler of the stack to adapt the elapsed time
}

...
/* Compute the prescaler value APB1 divided by two, but this is fixed by timer itself */
PrescalerValue = (uint16_t) ((SystemCoreClock) / 125000) - 1;
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 65535;
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

/* Prescaler configuration */
TIM_PrescalerConfig(TIM2, PrescalerValue, TIM_PSCReloadMode_Immediate);
...