From 21570fc24fbdecf6ace4d40fdfd3e7929bbe47f0 Mon Sep 17 00:00:00 2001
From: Kevin Hester <kevinh@geeksville.com>
Date: Sun, 27 Dec 2020 12:54:44 +0800
Subject: [PATCH] fix #540 use gps to fix rtc clock drift every 12 hrs

---
 src/gps/RTC.cpp | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/gps/RTC.cpp b/src/gps/RTC.cpp
index bc65dea17..387f4c0c4 100644
--- a/src/gps/RTC.cpp
+++ b/src/gps/RTC.cpp
@@ -31,9 +31,23 @@ void readFromRTC()
 /// If we haven't yet set our RTC this boot, set it from a GPS derived time
 bool perhapsSetRTC(RTCQuality q, const struct timeval *tv)
 {
+    static uint32_t lastSetMsec = 0;
+    uint32_t now = millis();
+
+    bool shouldSet;
     if (q > currentQuality) {
-        currentQuality = q;
-        DEBUG_MSG("Setting RTC %ld secs\n", tv->tv_sec);
+        shouldSet = true;
+        DEBUG_MSG("Upgrading time to RTC %ld secs (quality %d)\n", tv->tv_sec, q);
+    } else if(q == RTCQualityGPS && (now - lastSetMsec) > (12 * 60 * 60 * 1000L)) {
+        // Every 12 hrs we will slam in a new GPS time, to correct for local RTC clock drift
+        shouldSet = true;
+        DEBUG_MSG("Reapplying GPS time to correct clock drift %ld secs\n", tv->tv_sec);
+    }
+    else
+        shouldSet = false;
+
+    if (shouldSet) {
+        lastSetMsec = now;
 #ifndef NO_ESP32
         settimeofday(tv, NULL);
 #else