Workaround to fix RTC-reset issue on the EFM32GG11_STK3701

Author: petroborys

targets/TARGET_Silicon_Labs/TARGET_EFM32/rtcc.c

@@ -51,12 +51,20 @@ void rtc_init(void)
     RMU_ResetControl(rmuResetPin, rmuResetModeFull);
 
     /* Set up the RTCC and let it run, Forrest, run */
+
+    //Save time if it has been set.
+    time_t t = 0;
+    if (RTCC->RET[1].REG == 0) t = rtc_read();
+
     RTCC_Reset();
     RTCC_Init_TypeDef rtcc_init = RTCC_INIT_DEFAULT;
     rtcc_init.presc = rtccCntPresc_32768;
     RTCC_Init(&rtcc_init);
     RTCC_Enable(true);
-    RTCC->RET[0].REG = 0;
+
+    //Update time
+    if (RTCC->RET[1].REG == 0) rtc_write(t);
+    else RTCC->RET[0].REG = 0;
 }
 
 void rtc_free(void)
@@ -79,6 +87,8 @@ void rtc_write(time_t t)
 {
     core_util_critical_section_enter();
     RTCC->RET[0].REG = t - RTCC_CounterGet();
+    //Record that the time has been set
+    RTCC->RET[1].REG = 0;
     core_util_critical_section_exit();
 }