[PATCH v2 4/4] RTC:Add UIP(update in progress) check logic

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

The UIP(update in progress) is set when RTC is updating. We only
consider the normal oscillator(32Khz) mode.

When time base is 32kHz, the update cycle takes 1984us at the end
of every second. And the update cycle begins 244us later after UIP
is set. So the UIP is set in 2228us at end of every second.

Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>

---
 hw/mc146818rtc.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/hw/mc146818rtc.c b/hw/mc146818rtc.c
index 2445c6b..d4be8e9 100644
--- a/hw/mc146818rtc.c
+++ b/hw/mc146818rtc.c
@@ -601,6 +601,29 @@ static void rtc_calibrate_time(RTCState *s)
     s->current_tm = *ret;
 }

+static int update_in_progress(RTCState *s)
+{
+    struct timeval tv_now;
+    int64_t host_usec, offset_usec, guest_usec;
+
+    if (s->cmos_data[RTC_REG_B] & REG_B_SET) {
+        return 0;
+    }
+
+    gettimeofday(&tv_now, NULL);
+    host_usec = tv_now.tv_sec * USEC_PER_SEC + tv_now.tv_usec;
+    offset_usec = s->offset_sec * USEC_PER_SEC + s->offset_usec;
+    guest_usec = host_usec + offset_usec;
+
+    /* UIP bit will be set at last 2228us of every second.
+     * Only consider oscillator in 32.768kHz*/
+    if ((guest_usec % USEC_PER_SEC) >= (USEC_PER_SEC - 2228)) {
+        return 1;
+    }
+
+    return 0;
+}
+
 static uint32_t cmos_ioport_read(void *opaque, uint32_t addr)
 {
     RTCState *s = opaque;
@@ -622,6 +645,9 @@ static uint32_t cmos_ioport_read(void *opaque, uint32_t addr)
             break;
         case RTC_REG_A:
             ret = s->cmos_data[s->cmos_index];
+            if (update_in_progress(s)) {
+                ret |= REG_A_UIP;
+            }
             break;
         case RTC_REG_C:
             ret = s->cmos_data[s->cmos_index];
--
1.7.1
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