Added micros64 and used to fix and improve gettimeofday.

Author: BrandonLWhite

cores/esp8266/Arduino.h

@@ -202,6 +202,7 @@ void analogWriteRange(uint32_t range);
 
 unsigned long millis(void);
 unsigned long micros(void);
+uint64_t micros64(void);
 void delay(unsigned long);
 void delayMicroseconds(unsigned int us);
 unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout);

cores/esp8266/core_esp8266_wiring.c

@@ -71,6 +71,13 @@ unsigned long ICACHE_RAM_ATTR micros() {
     return system_get_time();
 }
 
+uint64_t ICACHE_RAM_ATTR micros64() {
+    uint32_t low32_us = system_get_time();
+    uint32_t high32_us = micros_overflow_count + ((low32_us < micros_at_last_overflow_tick) ? 1 : 0);
+    uint64_t duration64_us = (uint64_t)high32_us << 32 | low32_us;
+    return duration64_us;
+}
+
 void ICACHE_RAM_ATTR delayMicroseconds(unsigned int us) {
     os_delay_us(us);
 }

cores/esp8266/time.c

@@ -31,23 +31,27 @@ struct timeval {
 
 extern char* sntp_asctime(const struct tm *t);
 extern struct tm* sntp_localtime(const time_t *clock);
+extern uint64_t micros64();
 
 // time gap in seconds from 01.01.1900 (NTP time) to 01.01.1970 (UNIX time)
 #define DIFF1900TO1970 2208988800UL
 
 static int s_daylightOffset_sec = 0;
 static long s_timezone_sec = 0;
-static time_t s_bootTime = 0;
+static bool s_bootTimeSet = false;
+static uint64_t s_bootTime_us = 0;
 
 // calculate offset used in gettimeofday
 static void ensureBootTimeIsSet()
 {
-    if (!s_bootTime)
+    // Check just a bool flag instead of the full 64-bit s_bootTime for zero.
+    if (!s_bootTimeSet)
     {
-        time_t now = sntp_get_current_timestamp();
-        if (now)
+        time_t now_s = sntp_get_current_timestamp();
+        if (now_s)
         {
-            s_bootTime =  now - millis() / 1000;
+            s_bootTime_us = now_s * 1000000ULL - micros64();
+            s_bootTimeSet = true;
         }
     }
 }
@@ -100,8 +104,9 @@ int _gettimeofday_r(struct _reent* unused, struct timeval *tp, void *tzp)
     if (tp)
     {
         ensureBootTimeIsSet();
-        tp->tv_sec  = s_bootTime + millis() / 1000;
-        tp->tv_usec = micros();
+        uint64_t currentTime_us = s_bootTime_us + micros64();
+        tp->tv_sec = currentTime_us / 1000000ULL;
+        tp->tv_usec = currentTime_us % 1000000ULL;
     }
     return 0;
 }