Merge pull request #1836 from weebl2000/fix-rak3401-sky66122-11-fem

Fix RAK3401 SKY66122-11 FEM control: enable CSD/CPS for proper PA/LNA operation

Author: liamcottle

variants/rak3401/RAK3401Board.cpp

@@ -20,13 +20,29 @@ void RAK3401Board::begin() {
 
   Wire.begin();
 
+  // PIN_3V3_EN (WB_IO2, P0.34) controls the 3V3_S switched peripheral rail
+  // AND the 5V boost regulator (U5) on the RAK13302 that powers the SKY66122 PA.
+  // Must stay HIGH during radio operation — do not toggle for power saving.
   pinMode(PIN_3V3_EN, OUTPUT);
   digitalWrite(PIN_3V3_EN, HIGH);
 
-#ifdef P_LORA_PA_EN
-  // Initialize RAK13302 1W LoRa transceiver module PA control pin
-  pinMode(P_LORA_PA_EN, OUTPUT);
-  digitalWrite(P_LORA_PA_EN, LOW);  // Start with PA disabled
-  delay(10);  // Allow PA module to initialize
+  // Enable SKY66122-11 FEM on the RAK13302 module.
+  // CSD and CPS are tied together on the RAK13302 PCB, routed to IO3 (P0.21).
+  // HIGH = FEM active (LNA for RX, PA path available for TX).
+  // TX/RX switching (CTX) is handled by SX1262 DIO2 via SetDIO2AsRfSwitchCtrl.
+  pinMode(SX126X_POWER_EN, OUTPUT);
+  digitalWrite(SX126X_POWER_EN, HIGH);
+  delay(1);  // SKY66122 turn-on settling time (tON = 3us typ)
+}
+
+#ifdef NRF52_POWER_MANAGEMENT
+void RAK3401Board::initiateShutdown(uint8_t reason) {
+  // Disable SKY66122 FEM (CSD+CPS LOW = shutdown, <1 uA)
+  digitalWrite(SX126X_POWER_EN, LOW);
+
+  // Disable 3V3 switched peripherals and 5V boost
+  digitalWrite(PIN_3V3_EN, LOW);
+
+  enterSystemOff(reason);
+}
 #endif
-}

variants/rak3401/RAK3401Board.h

@@ -38,13 +38,6 @@ class RAK3401Board : public NRF52BoardDCDC {
     return "RAK 3401";
   }
 
-#ifdef P_LORA_PA_EN
-  void onBeforeTransmit() override {
-    digitalWrite(P_LORA_PA_EN, HIGH);  // Enable PA before transmission
-  }
-
-  void onAfterTransmit() override {
-    digitalWrite(P_LORA_PA_EN, LOW);   // Disable PA after transmission to save power
-  }
-#endif
+  // TX/RX switching is handled by SX1262 DIO2 -> SKY66122 CTX (hardware-timed).
+  // No onBeforeTransmit/onAfterTransmit overrides needed.
 };

variants/rak3401/platformio.ini

@@ -11,6 +11,7 @@ build_flags = ${nrf52_base.build_flags}
   -D LORA_TX_POWER=22
   -D SX126X_CURRENT_LIMIT=140
   -D SX126X_RX_BOOSTED_GAIN=1
+  -D SX126X_REGISTER_PATCH=1       ; Patch register 0x8B5 for improved RX with SKY66122 FEM
 build_src_filter = ${nrf52_base.build_src_filter}
   +<../variants/rak3401>
   +<helpers/sensors>

variants/rak3401/variant.h

@@ -147,8 +147,15 @@ static const uint8_t AREF = PIN_AREF;
 #define SX126X_BUSY (9)
 #define SX126X_RESET (4)
 
-#define SX126X_POWER_EN (21)
-// DIO2 controlls an antenna switch and the TCXO voltage is controlled by DIO3
+// SKY66122-11 FEM control on the RAK13302 module:
+//   CSD + CPS are tied together on the PCB, routed to WisBlock IO3 (P0.21).
+//   Setting IO3 HIGH enables the FEM (LNA for RX, PA path for TX).
+//   CTX is connected to SX1262 DIO2 — the radio handles TX/RX switching
+//   in hardware via SetDIO2AsRfSwitchCtrl (microsecond-accurate, no GPIO needed).
+//   The 5V boost for the PA is enabled by WB_IO2 (P0.34 = PIN_3V3_EN).
+#define SX126X_POWER_EN (21)        // P0.21 = IO3 -> SKY66122 CSD+CPS (FEM enable)
+
+// CTX is driven by SX1262 DIO2, not a GPIO
 #define SX126X_DIO2_AS_RF_SWITCH
 #define SX126X_DIO3_TCXO_VOLTAGE 1.8
 
@@ -159,7 +166,6 @@ static const uint8_t AREF = PIN_AREF;
 #define P_LORA_DIO_1 SX126X_DIO1
 #define P_LORA_BUSY SX126X_BUSY
 #define P_LORA_RESET SX126X_RESET
-#define P_LORA_PA_EN  31
 
 // enables 3.3V periphery like GPS or IO Module
 // Do not toggle this for GPS power savings