diff options
Diffstat (limited to 'hw/timer/mc146818rtc.c')
-rw-r--r-- | hw/timer/mc146818rtc.c | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c index 1b8d3d7..82843ed 100644 --- a/hw/timer/mc146818rtc.c +++ b/hw/timer/mc146818rtc.c @@ -291,26 +291,15 @@ static void check_update_timer(RTCState *s) /* From the data sheet: "Holding the dividers in reset prevents * interrupts from operating, while setting the SET bit allows" - * them to occur. However, it will prevent an alarm interrupt - * from occurring, because the time of day is not updated. + * them to occur. */ if ((s->cmos_data[RTC_REG_A] & 0x60) == 0x60) { - timer_del(s->update_timer); - return; - } - if ((s->cmos_data[RTC_REG_C] & REG_C_UF) && - (s->cmos_data[RTC_REG_B] & REG_B_SET)) { - timer_del(s->update_timer); - return; - } - if ((s->cmos_data[RTC_REG_C] & REG_C_UF) && - (s->cmos_data[RTC_REG_C] & REG_C_AF)) { + assert((s->cmos_data[RTC_REG_A] & REG_A_UIP) == 0); timer_del(s->update_timer); return; } guest_nsec = get_guest_rtc_ns(s) % NANOSECONDS_PER_SECOND; - /* if UF is clear, reprogram to next second */ next_update_time = qemu_clock_get_ns(rtc_clock) + NANOSECONDS_PER_SECOND - guest_nsec; @@ -321,7 +310,21 @@ 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) { + /* If update_in_progress latched the UIP bit, we must keep the timer + * programmed to the next second, so that UIP is cleared. Otherwise, + * if UF is already set, we might be able to optimize. + */ + if (!(s->cmos_data[RTC_REG_A] & REG_A_UIP) && + (s->cmos_data[RTC_REG_C] & REG_C_UF)) { + /* If AF cannot change (i.e. either it is set already, or + * SET=1 and then the time is not updated), nothing to do. + */ + if ((s->cmos_data[RTC_REG_B] & REG_B_SET) || + (s->cmos_data[RTC_REG_C] & REG_C_AF)) { + timer_del(s->update_timer); + return; + } + /* UF is set, but AF is clear. Program the timer to target * the alarm time. */ next_update_time = s->next_alarm_time; @@ -727,12 +730,10 @@ static uint64_t cmos_ioport_read(void *opaque, hwaddr addr, ret = s->cmos_data[s->cmos_index]; break; case RTC_REG_A: + ret = s->cmos_data[s->cmos_index]; 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 |= REG_A_UIP; } - ret = s->cmos_data[s->cmos_index]; break; case RTC_REG_C: ret = s->cmos_data[s->cmos_index]; |