Код
DWORD get_fattime (void)
{
uint_fast16_t year;
uint_fast8_t month, day;
uint_fast8_t hour, minute, secounds;
board_rtc_getdatetime(& year, & month, & day, & hour, & minute, & secounds);
return ((DWORD)(year - 1980) << 25) /* Year = 2012 */
| ((DWORD)month << 21) /* Month = 1 */
| ((DWORD)day << 16) /* Day_m = 1*/
| ((DWORD)hour << 11) /* Hour = 0 */
| ((DWORD)minute << 5) /* Min = 0 */
| ((DWORD)secounds >> 1); /* Sec = 0 */
}
Там вообще-то от 80-го года начало.