upstream sync and gps stuff

zephcore/adapters/clock/ZephyrRTCClock.cpp

@@ -23,16 +23,48 @@ static void rtc_save_work_fn(struct k_work *work)
 static K_WORK_DEFINE(s_rtc_save_work, rtc_save_work_fn);
 #endif
 
+/* The last time read, kept across a reset that keeps RAM (reboot, crash,
+ * watchdog), as upstream's ESP32RTCClock does. ESP32 keeps it in RTC slow
+ * memory: the bootloader may reuse ordinary noinit RAM. Power-on leaves
+ * garbage, which the magic rejects. */
+#if defined(CONFIG_SOC_FAMILY_ESPRESSIF_ESP32)
+#define RTC_BACKUP_ATTR Z_GENERIC_SECTION(.rtc_noinit)
+#else
+#define RTC_BACKUP_ATTR __noinit
+#endif
+static RTC_BACKUP_ATTR uint32_t _rtc_backup_time;
+static RTC_BACKUP_ATTR uint32_t _rtc_backup_magic;
+#define RTC_BACKUP_MAGIC  0xAA55CC33
+#define RTC_TIME_MIN      1772323200  // 1 Mar 2026
+
+ZephyrRTCClock::ZephyrRTCClock()
+{
+	if (_rtc_backup_magic == RTC_BACKUP_MAGIC && _rtc_backup_time > RTC_TIME_MIN) {
+		epoch_offset = _rtc_backup_time;
+	}
+}
+
 uint32_t ZephyrRTCClock::getCurrentTime()
 {
 	uint32_t uptime_sec = (uint32_t)(k_uptime_get() / 1000);
-	return epoch_offset + uptime_sec;
+	uint32_t now = epoch_offset + uptime_sec;
+
+	/* upstream does this in tick(), which nothing calls here */
+	if (now > RTC_TIME_MIN && now != _rtc_backup_time) {
+		_rtc_backup_time = now;
+		_rtc_backup_magic = RTC_BACKUP_MAGIC;
+	}
+	return now;
 }
 
 void ZephyrRTCClock::seedCurrentTime(uint32_t time)
 {
 	uint32_t uptime_sec = (uint32_t)(k_uptime_get() / 1000);
 	epoch_offset = time - uptime_sec;
+	/* As upstream's setCurrentTime(): unconditional, so a set below
+	 * RTC_TIME_MIN (clkreboot) replaces the backup and is not restored. */
+	_rtc_backup_time = time;
+	_rtc_backup_magic = RTC_BACKUP_MAGIC;
 }
 
 void ZephyrRTCClock::setCurrentTime(uint32_t time)

zephcore/adapters/clock/ZephyrRTCClock.h

@@ -11,6 +11,8 @@ namespace mesh {
 
 class ZephyrRTCClock : public RTCClock {
 public:
+	/* Starts from the time kept across the last reset, if any (see the .cpp). */
+	ZephyrRTCClock();
 	uint32_t getCurrentTime() override;
 	/* Also written to the board's hardware RTC, if it has one, as upstream's
 	 * AutoDiscoverRTCClock does: coalesced on the system work queue, so