On 25/07/2017 06:14, peng.h...@zte.com.cn wrote: >> On 24/07/2017 20:35, Peng Hao wrote: > > > > > >>> When a windows vm starts, periodic timer of rtc will stop several times. >>> windows kernel will check whether REG_A_UIP is changed. REG_C's interrupt >>> flags will not be cleared when periodic timer stops and the update timer >>> will switch to alarm timer. So the expiration time of alarm timer is very >>> long and REG_A_UIP will not vary.At last windows kernel will repeat to >>> check REG_A_UIP all the time. > >> This should not happen. REG_A_UIP is set and cleared in register A >> every second, like this: >> case RTC_REG_A: > >> if (update_in_progress(s)) { >> s->cmos_data[s->cmos_index] |= REG_A_UIP >> } else { >> s->cmos_data[s->cmos_index] &= ~REG_A_UIP >> } >> ret = s->cmos_data[s->cmos_index] >> break > > > > when periodic timer stop, update timer is set to a long expire time (as alarm > timer).
I think I see the bug now: diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c index 1b8d3d7d4c..6184b4378e 100644 --- a/hw/timer/mc146818rtc.c +++ b/hw/timer/mc146818rtc.c @@ -321,9 +321,11 @@ static void check_update_timer(RTCState *s) s->next_alarm_time = next_update_time + (next_alarm_sec - 1) * NANOSECONDS_PER_SECOND; - if (s->cmos_data[RTC_REG_C] & REG_C_UF) { - /* UF is set, but AF is clear. Program the timer to target - * the alarm time. */ + if ((s->cmos_data[RTC_REG_C] & REG_C_UF) && + !(s->cmos_data[RTC_REG_A] & REG_A_UIP)) { + /* If UIP was latched, we need to clear it at the next update. + * Otherwise, if UF is set we only need to program the timer to + * target the alarm time. */ next_update_time = s->next_alarm_time; } if (next_update_time != timer_expire_time_ns(s->update_timer)) { but I would like to have a testcase for it in tests/rtc-test.c. Can you check if the above works and try writing a testcase (that fails without the patch and succeeds with it)? Thanks, Paolo