RTC counting too fast on lm4f120xl launchpad

hi,

i want to use the hibernation modul for a realtime clock and date with my launchpad for an data logger

evereything ist working fine, but the rtc counts approximately 1% too fast.

Did i forget something, to activate the external 32khz chrystal?

here are my settings for the hibernationmodul:

/* Realtime Clock and hibernate*/
ROM_SysCtlPeripheralEnable(SYSCTL_PERIPH_HIBERNATE);
ROM_HibernateEnableExpClk(SysCtlClockGet());
HibernateClockConfig(HIBERNATE_OSC_DISABLE | HIBERNATE_OSC_HIGHDRIVE);
HibernateClockSelect(HIBERNATE_CLOCK_SEL_RAW);
HibernateGPIORetentionEnable();
ROM_HibernateWakeSet(HIBERNATE_WAKE_PIN);
ROM_SysCtlDelay(6400);
ROM_HibernateRTCEnable();
/* End Realtime Clock */