STM32F030 Counterproblem

#include "stm32f0xx.h"

#include "system_stm32f0xx.h"

#include "stm32f0xx_gpio.h"

#include "stm32f0xx_rcc.h"

#include "stm32f0xx_tim.h"

#include "stm32f0xx_misc.h"

// Function Prototypes

void ClockInit(void);

void Timer1Init(void);

// Read and refresh frequency in ms

const uint16_t READ_FREQUENCE  = 250;

volatile uint8_t job;

volatile uint32_t sensor_counter;

int main(void)

{

  //Init Variables

  job = 0x00;

  //Init the main clock

  SystemInit();

  //Init Periph Clock

  ClockInit();

  //Init Timer1

  Timer1Init();

  //Systick Config running MCU with 48 MHz generates 1ms Tick

  SysTick_Config(48000);

    while(1)

    {

      //Check if sensor must be read out

      if ((job & 0x01) == 1)

      {

        job = job ^ 0x01;

        sensor_counter = TIM_GetCounter(TIM1);

        TIM_SetCounter(TIM1,0);

       }

    }

}

void ClockInit(void)

{

  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);

  RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);

}

void Timer1Init(void)

{

  GPIO_InitTypeDef GPIO_InitStructure;

  TIM_TimeBaseInitTypeDef  TIM_InitStructure;

  // Config Timer1 Pin

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;

  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;

  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

  GPIO_Init(GPIOA, &GPIO_InitStructure);

  // Config Timer1 as Counter

  TIM_InitStructure.TIM_ClockDivision = 0;

  TIM_InitStructure.TIM_Period = 0xFFFF;

  TIM_InitStructure.TIM_Prescaler = 0;

  TIM_InitStructure.TIM_CounterMode = TIM_CounterMode_Up;

  TIM_TimeBaseInit(TIM1, &TIM_InitStructure);

  TIM_TIxExternalClockConfig(TIM1, TIM_TS_TI2FP2, TIM_ICPolarity_Rising, 0);

  TIM_SelectSlaveMode(TIM1, TIM_SlaveMode_External1);

  TIM_Cmd(TIM1,ENABLE);

}

void SysTick_Handler(void)

{

  static uint16_t read_freq_counter;

  // Is used to check if a new Sensor readout must happen

  read_freq_counter++;

  if (read_freq_counter >= READ_FREQUENCE)

  {

    read_freq_counter = 0;

    if ((job & 0x01) != 0x01)  job = job ^ 0x01;

  }

}