From b09b8a057dca5c6d4fc3ad0d1b0dbc3028b43a51 Mon Sep 17 00:00:00 2001
From: mathison <mathisono@gmail.com>
Date: Tue, 14 Jul 2026 00:22:34 -0700
Subject: [PATCH] Add RAK12501 L76K PCAS configuration

---
 variants/rak3401/target.cpp | 93 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 2 deletions(-)

diff --git a/variants/rak3401/target.cpp b/variants/rak3401/target.cpp
index 5309e6b22..4b13b7bc1 100644
--- a/variants/rak3401/target.cpp
+++ b/variants/rak3401/target.cpp
@@ -1,4 +1,5 @@
 #include <Arduino.h>
+#include <RTClib.h>
 #include "target.h"
 #include <helpers/ArduinoHelpers.h>
 
@@ -26,7 +27,96 @@ AutoDiscoverRTCClock rtc_clock(fallback_clock);
 
 #if ENV_INCLUDE_GPS
   #include <helpers/sensors/MicroNMEALocationProvider.h>
-  MicroNMEALocationProvider nmea = MicroNMEALocationProvider(Serial1, &rtc_clock);
+
+  // RAK3401 1W Booster GPS builds use the RAK12501 / Quectel L76K by default.
+  // This config is deliberately local to the RAK3401 target so the shared GPS
+  // manager does not learn another board-specific L76K init path.
+  #ifndef RAK12501_L76K_GPS
+    #define RAK12501_L76K_GPS 1
+  #endif
+
+  #if defined(RAK12501_L76K_GPS)
+    #ifndef RAK12501_L76K_NAV_MODE
+      #define RAK12501_L76K_NAV_MODE 3
+    #endif
+
+    #ifndef RAK12501_L76K_BOOT_DELAY_MS
+      #define RAK12501_L76K_BOOT_DELAY_MS 1000
+    #endif
+
+    static void rak12501SendNMEACommand(Stream& serial, const char* body) {
+      uint8_t checksum = 0;
+      for (const char* p = body; *p; ++p) {
+        checksum ^= (uint8_t)*p;
+      }
+
+      serial.print('$');
+      serial.print(body);
+      serial.print('*');
+      if (checksum < 0x10) {
+        serial.print('0');
+      }
+      serial.print(checksum, HEX);
+      serial.print("\r\n");
+    }
+
+    static void rak12501InjectKnownTime() {
+      uint32_t now = rtc_clock.getCurrentTime();
+
+      // Only inject if the board clock is plausible. Avoid feeding the GPS the
+      // zero/default RTC value on first boot. 2020-01-01 is a conservative floor.
+      if (now < 1577836800UL) {
+        return;
+      }
+
+      DateTime dt(now);
+      char body[40];
+      snprintf(body, sizeof(body), "PMTK740,%04u,%02u,%02u,%02u,%02u,%02u",
+               dt.year(), dt.month(), dt.day(), dt.hour(), dt.minute(), dt.second());
+      rak12501SendNMEACommand(Serial1, body);
+      delay(250);
+    }
+
+    static void rak12501ConfigureL76K() {
+      MESH_DEBUG_PRINTLN("Configuring RAK12501/L76K GPS");
+
+      // Best-effort MTK aiding: if RTC has a known time, provide UTC time before
+      // the main config. Location/almanac injection is intentionally not included;
+      // it needs a fresh/accurate location source or downloadable EPO/almanac data.
+      rak12501InjectKnownTime();
+
+      // Meshtastic-style L76K init:
+      //   GPS + GLONASS + BeiDou
+      //   NMEA RMC + GGA only to reduce serial traffic for the companion app
+      //   Vehicle mode by default ($PCAS11,3)
+      rak12501SendNMEACommand(Serial1, "PCAS04,7");
+      delay(250);
+      rak12501SendNMEACommand(Serial1, "PCAS03,1,0,0,0,1,0,0,0,0,0,,,0,0");
+      delay(250);
+
+      char nav_mode[16];
+      uint8_t mode = (RAK12501_L76K_NAV_MODE <= 7) ? RAK12501_L76K_NAV_MODE : 3;
+      snprintf(nav_mode, sizeof(nav_mode), "PCAS11,%u", mode);
+      rak12501SendNMEACommand(Serial1, nav_mode);
+      delay(250);
+    }
+
+    class RAK12501L76KLocationProvider : public MicroNMEALocationProvider {
+    public:
+      using MicroNMEALocationProvider::MicroNMEALocationProvider;
+
+      void reset() override {
+        MicroNMEALocationProvider::reset();
+        delay(RAK12501_L76K_BOOT_DELAY_MS);
+        rak12501ConfigureL76K();
+      }
+    };
+
+    RAK12501L76KLocationProvider nmea = RAK12501L76KLocationProvider(Serial1, &rtc_clock);
+  #else
+    MicroNMEALocationProvider nmea = MicroNMEALocationProvider(Serial1, &rtc_clock);
+  #endif
+
   EnvironmentSensorManager sensors = EnvironmentSensorManager(nmea);
 #else
   EnvironmentSensorManager sensors;
@@ -41,4 +131,3 @@ mesh::LocalIdentity radio_new_identity() {
   RadioNoiseListener rng(radio);
   return mesh::LocalIdentity(&rng);  // create new random identity
 }
-