From 03d1ace9229f3dbc8b620ce6e3c4c654d4be83ab Mon Sep 17 00:00:00 2001
From: Henry Potgieter <hpotgieter@viscousbits.ca>
Date: Mon, 30 Mar 2026 00:47:08 -0400
Subject: [PATCH] Allow support for <= v4.2 and v4.3 Heltec ESP32 boards due to
 KCT8103L PA in v4.3

---
 Boards.h           |  7 ++---
 RNode_Firmware.ino | 10 ++++---
 sx126x.cpp         | 66 ++++++++++++++++++++++------------------------
 sx126x.h           |  3 +++
 4 files changed, 45 insertions(+), 41 deletions(-)

diff --git a/Boards.h b/Boards.h
index 9d69bf6..ca97b71 100644
--- a/Boards.h
+++ b/Boards.h
@@ -422,10 +422,11 @@
 
       #define LORA_LNA_GAIN  17
       #define LORA_LNA_GVT   12
-      #define LORA_PA_KCT8103L true
+      #define LORA_PA_AUTO_DETECT true
       #define LORA_PA_PWR_EN  7
-      #define LORA_PA_CSD     2
-      #define LORA_PA_CTX     5
+      #define LORA_PA_CSD     2  // GC1109: PA_EN | KCT8103L: CSD (same pin, different pull resistor)
+      #define LORA_PA_CTX     5  // KCT8103L: TX/LNA select (CTX=LOW=LNA, CTX=HIGH=PA)
+      #define LORA_PA_CPS    46  // GC1109: TX_EN
 
       #define PA_MAX_OUTPUT  28
       #define PA_GAIN_POINTS 22
diff --git a/RNode_Firmware.ino b/RNode_Firmware.ino
index 1f13040..5e77883 100644
--- a/RNode_Firmware.ino
+++ b/RNode_Firmware.ino
@@ -1767,10 +1767,12 @@ void sleep_now() {
         #endif
       #endif
       #if BOARD_MODEL == BOARD_HELTEC32_V4
-          #if LORA_PA_KCT8103L
-            digitalWrite(LORA_PA_CTX, LOW);
-          #elif LORA_PA_GC1109
-            digitalWrite(LORA_PA_CPS, LOW);
+          #if LORA_PA_AUTO_DETECT
+            if (sx126x_modem.isKCT8103L()) {
+              digitalWrite(LORA_PA_CTX, LOW);
+            } else {
+              digitalWrite(LORA_PA_CPS, LOW);
+            }
           #endif
           digitalWrite(LORA_PA_CSD, LOW);
           digitalWrite(LORA_PA_PWR_EN, LOW);
diff --git a/sx126x.cpp b/sx126x.cpp
index ddb7c07..6d31e63 100644
--- a/sx126x.cpp
+++ b/sx126x.cpp
@@ -343,33 +343,29 @@ int sx126x::begin(long frequency) {
   setPacketParams(_preambleLength, _implicitHeaderMode, _payloadLength, _crcMode);
 
   #if HAS_LORA_PA
-    #if LORA_PA_KCT8103L
-      // Enable Vfem_ctl for supply to PA power net.
+    #if LORA_PA_AUTO_DETECT
+      // Power up the FEM, then read GPIO LORA_PA_CSD as input.
+      // The V4.2 (GC1109) board pulls it LOW; V4.3 (KCT8103L) pulls it HIGH.
       pinMode(LORA_PA_PWR_EN, OUTPUT);
       digitalWrite(LORA_PA_PWR_EN, HIGH);
+      delay(1);
+      pinMode(LORA_PA_CSD, INPUT);
+      delay(1);
+      _kct8103l = (digitalRead(LORA_PA_CSD) == HIGH);
 
-      // Enable KCT8103L: CSD=HIGH activates the chip.
-      pinMode(LORA_PA_CSD, OUTPUT);
-      digitalWrite(LORA_PA_CSD, HIGH);
-
-      // CTX=LOW selects LNA/RX mode by default.
-      // CTX=HIGH switches to PA/TX mode.
-      // Must be toggled on each TX/RX transition.
-      pinMode(LORA_PA_CTX, OUTPUT);
-      digitalWrite(LORA_PA_CTX, LOW);
-    #elif LORA_PA_GC1109
-      // Enable Vfem_ctl for supply to
-      // PA power net.
-      pinMode(LORA_PA_PWR_EN, OUTPUT);
-      digitalWrite(LORA_PA_PWR_EN, HIGH);
-
-      // Enable PA LNA and TX standby
-      pinMode(LORA_PA_CSD, OUTPUT);
-      digitalWrite(LORA_PA_CSD, HIGH);
-
-      // Keep PA CPS high permanently.
-      pinMode(LORA_PA_CPS, OUTPUT);
-      digitalWrite(LORA_PA_CPS, HIGH);
+      if (_kct8103l) {
+        // KCT8103L (V4.3): CSD=HIGH enables chip, CTX=LOW=LNA/RX, CTX=HIGH=PA/TX
+        pinMode(LORA_PA_CSD, OUTPUT);
+        digitalWrite(LORA_PA_CSD, HIGH);
+        pinMode(LORA_PA_CTX, OUTPUT);
+        digitalWrite(LORA_PA_CTX, LOW); // LNA enabled by default
+      } else {
+        // GC1109 (V4.2): PA_EN=HIGH enables chip, CPS=HIGH=full PA mode
+        pinMode(LORA_PA_CSD, OUTPUT);
+        digitalWrite(LORA_PA_CSD, HIGH);
+        pinMode(LORA_PA_CPS, OUTPUT);
+        digitalWrite(LORA_PA_CPS, HIGH);
+      }
     #endif
   #endif
 
@@ -380,11 +376,12 @@ void sx126x::end() { sleep(); SPI.end(); _preinit_done = false; }
 
 int sx126x::beginPacket(int implicitHeader) {
   #if HAS_LORA_PA
-    #if LORA_PA_KCT8103L
-      // CTX=HIGH: switch KCT8103L to PA/TX mode.
-      digitalWrite(LORA_PA_CTX, HIGH);
-    #elif LORA_PA_GC1109
-      // CPS kept HIGH permanently, no action needed.
+    #if LORA_PA_AUTO_DETECT
+      if (_kct8103l) {
+        // CTX=HIGH: switch KCT8103L to PA/TX mode.
+        digitalWrite(LORA_PA_CTX, HIGH);
+      }
+      // GC1109: CPS kept HIGH permanently, no action needed.
     #endif
   #endif
 
@@ -596,11 +593,12 @@ void sx126x::onReceive(void(*callback)(int)){
 
 void sx126x::receive(int size) {
   #if HAS_LORA_PA
-    #if LORA_PA_KCT8103L
-      // CTX=LOW: switch KCT8103L to LNA/RX mode.
-      digitalWrite(LORA_PA_CTX, LOW);
-    #elif LORA_PA_GC1109
-      // CPS kept HIGH permanently, no action needed.
+    #if LORA_PA_AUTO_DETECT
+      if (_kct8103l) {
+        // CTX=LOW: switch KCT8103L to LNA/RX mode.
+        digitalWrite(LORA_PA_CTX, LOW);
+      }
+      // GC1109: CPS kept HIGH permanently, no action needed.
     #endif
   #endif
 
diff --git a/sx126x.h b/sx126x.h
index 068a1bb..c31202a 100644
--- a/sx126x.h
+++ b/sx126x.h
@@ -97,6 +97,8 @@ public:
 
   void dumpRegisters(Stream& out);
 
+  bool isKCT8103L() { return _kct8103l; }
+
 private:
   void explicitHeaderMode();
   void implicitHeaderMode();
@@ -137,6 +139,7 @@ private:
   int _fifo_rx_addr_ptr;
   uint8_t _packet[255];
   bool _preinit_done;
+  bool _kct8103l;
   void (*_onReceive)(int);
 };