From 225c47ede3ac069e2690fd3f5d9038fdea04a035 Mon Sep 17 00:00:00 2001
From: Ben Meadors <benmmeadors@gmail.com>
Date: Wed, 16 Jul 2025 19:17:45 -0500
Subject: [PATCH] Factory reset RTC

---
 src/gps/GPS.cpp | 7 +++++++
 src/gps/cas.h   | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/src/gps/GPS.cpp b/src/gps/GPS.cpp
index 3a6b19f64..9f7a7ebbf 100644
--- a/src/gps/GPS.cpp
+++ b/src/gps/GPS.cpp
@@ -1539,6 +1539,13 @@ The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of s
             if (perhapsSetRTC(RTCQualityGPS, t) == RTCSetResultInvalidTime) {
                 // Clear the GPS buffer if we got an invalid time
                 clearBuffer();
+                // Clear the RTC from the L76K, L76B, and clones
+                if (IS_ONE_OF(gnssModel, GNSS_MODEL_MTK_L76B, GNSS_MODEL_MTK)) {
+                    // Clear the RTC from the L76 and MTK GPS modules
+                    LOG_DEBUG("Clearing RTC from L76K/L76B");
+                    int msglen = makeCASPacket(0x06, 0x02, sizeof(_message_CAS_CFG_RST_FACTORY), _message_CAS_CFG_RST_FACTORY);
+                    _serial_gps->write(_message_CAS_CFG_RST_FACTORY, msglen);
+                }
             }
             return true;
         } else
diff --git a/src/gps/cas.h b/src/gps/cas.h
index 725fd07b3..cd8ef0eba 100644
--- a/src/gps/cas.h
+++ b/src/gps/cas.h
@@ -27,6 +27,13 @@ static const uint8_t _message_CAS_CFG_RST_FACTORY[] = {
     0x03        // Startup Mode: Factory
 };
 
+// Clear RTC data
+static const uint8_t _message_CAS_CFG_RST_RTC[] = {
+    0x00, 0x01, // NavBbrMask: Clear RTC data
+    0x01,       // Reset Mode: Controlled Software reset
+    0x00        // Reserved
+};
+
 // CFG_RATE (0x06, 0x01)
 // 1HZ update rate, this should always be the case after
 // factory reset but update it regardless