ARM: SOFTWARE RESET IN C

Thanks for your help. I'm sorry, but do you know how I could activate the watchdog timer?

Do you mean for example "while(1);" as busy-loop?

if you are using ST's library, you can get away with something like this:

  SCU_APBPeriphClockConfig(__WDG, ENABLE); /* Enable the clock for the WDG peripheral*/
  WDG_DeInit();/* WDG default configuration : Reset configuration*/

  WDG_InitStructure.WDG_Mode = WDG_Mode_Timer;
  WDG_InitStructure.WDG_Preload = 0xFFFF;
  WDG_InitStructure.WDG_Prescaler = 0xFF;
  WDG_InitStructure.WDG_ClockSource=WDG_ClockSource_Apb;

  WDG_Init(&WDG_InitStructure);  /* WDG initialization with the previous chosen parameters.*/

be sure, however, to configure the watchdog's period by the prescaler to service your exact needs.

"if you are using ST's library, you can get away with something like this:"

But he isn't, so he won't :)

The watchdog can be started with:

void wdog_kick(void) {
    // Errata 23xx WDT.1 No APB accesses allowed during feed sequence.
    unsigned prev = VICIntEnable;
    VICIntEnClr=prev;   // Disabling interrupts in the VIC
    WDFEED = 0xAA;
    WDFEED = 0x55;
    VICIntEnable=prev;  // Enabling interrupts in the VIC
}

void wdog_init(void) {
    WDTC = PCLK/4;          // Watchdog timer constant.
    WDMOD = WDEN|WDRESET;   // Reset processor if failure to kick.
    wdog_kick();            // Activate watchdog.
}

Note that even if you want to use the watchdog just go reset your chip, you must kick it once, just to activate it.

But all this is very well described in the user manual!