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-rw-r--r--hw/mc146818rtc.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/hw/mc146818rtc.c b/hw/mc146818rtc.c
index 98839f278d..c79fca7d68 100644
--- a/hw/mc146818rtc.c
+++ b/hw/mc146818rtc.c
@@ -25,6 +25,7 @@
 #include "qemu-timer.h"
 #include "sysemu.h"
 #include "mc146818rtc.h"
+#include "qapi/qapi-visit-core.h"
 
 #ifdef TARGET_I386
 #include "apic.h"
@@ -569,7 +570,11 @@ static void rtc_update_time(RTCState *s)
     guest_nsec = get_guest_rtc_ns(s);
     guest_sec = guest_nsec / NSEC_PER_SEC;
     gmtime_r(&guest_sec, &ret);
-    rtc_set_cmos(s, &ret);
+
+    /* Is SET flag of Register B disabled? */
+    if ((s->cmos_data[RTC_REG_B] & REG_B_SET) == 0) {
+        rtc_set_cmos(s, &ret);
+    }
 }
 
 static int update_in_progress(RTCState *s)