- s->cmos_data[RTC_REG_B] = data;
- rtc_timer_update(s, qemu_get_clock(rtc_clock));
+ if (((s->cmos_data[RTC_REG_B] ^ data) & (REG_B_DM | REG_B_24H)) &&
+ !(data & REG_B_SET)) {
+ /* If the time format has changed and not in set mode,
+ update the registers immediately. */
+ s->cmos_data[RTC_REG_B] = data;
+ rtc_copy_date(s);
+ } else {
+ s->cmos_data[RTC_REG_B] = data;
+ }
+ rtc_timer_update(s, qemu_get_clock_ns(rtc_clock));