spark watchdog config

#define __IWDG_PERIOD             0x01C9C380   // equals to 30000000 microseconds which should be 30 seconds

/*----------------------------------------------------------------------------
 Define  IWDG PR and RLR settings and helps calculate the needed prescaler
 *----------------------------------------------------------------------------*/
#if   (__IWDG_PERIOD >  16384000UL)
  #define __IWDG_PR             (6)
  #define __IWDGCLOCK (32000UL/256)
#elif (__IWDG_PERIOD >   8192000UL)
  #define __IWDG_PR             (5)
  #define __IWDGCLOCK (32000UL/128)
#elif (__IWDG_PERIOD >   4096000UL)
  #define __IWDG_PR             (4)
  #define __IWDGCLOCK  (32000UL/64)
#elif (__IWDG_PERIOD >   2048000UL)
  #define __IWDG_PR             (3)
  #define __IWDGCLOCK  (32000UL/32)
#elif (__IWDG_PERIOD >   1024000UL)
  #define __IWDG_PR             (2)
  #define __IWDGCLOCK  (32000UL/16)
#elif (__IWDG_PERIOD >    512000UL)
  #define __IWDG_PR             (1)
  #define __IWDGCLOCK   (32000UL/8)
#else
  #define __IWDG_PR             (0)
  #define __IWDGCLOCK   (32000UL/4)
#endif
    #define __IWGDCLK  (32000UL/(0x04<<__IWDG_PR))
    #define __IWDG_RLR (__IWDG_PERIOD*__IWGDCLK/1000000UL-1)

void stm32_IwdgSetup () {

    //  RCC->CSR |= (1<<0);                                           // LSI enable, necessary for IWDG
    //  while ((RCC->CSR & (1<<1)) == 0);                             // wait till LSI is ready

	IWDG->KR  = 0x5555;                                           // enable write to PR, RLR
	IWDG->PR  = __IWDG_PR;                                        // Init prescaler
	IWDG->RLR = __IWDG_RLR;                                       // Init RLR
	IWDG->KR  = 0xAAAA;                                           // Reload the watchdog
	IWDG->KR  = 0xCCCC;                                           // Start the watchdog
} // end of stm32_IwdgSetup

// DONT FORGET THIS!!!!! add this line to your main loop so that the watchdog gets reset
IWDG->KR  = 0xAAAA;