From 70f1ad4aebf22a70a663f310487bbb8eb167ddf8 Mon Sep 17 00:00:00 2001 From: Wessel Nieboer Date: Wed, 25 Feb 2026 00:26:38 +0100 Subject: [PATCH] Fix RAK3401 SKY66122-11 FEM control: enable CSD/CPS for proper PA and LNA operation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The RAK13302 1W module uses a Skyworks SKY66122-11 front-end module with three digital control pins (CSD, CTX, CPS) that must be actively driven by the host MCU. The previous code only managed CTX (GPIO 31) — toggling it for TX/RX — but never initialized CSD (GPIO 24) or CPS (GPIO 21), leaving them floating with no pull-up/pull-down resistors on the PCB. With floating CSD and CPS, the SKY66122 was in an undefined operating mode: - The 30 dB TX PA may not have been reliably engaging - The 16 dB RX LNA was never reliably active, degrading receive sensitivity --- variants/rak3401/RAK3401Board.cpp | 33 ++++++++++++++++++++++++++----- variants/rak3401/RAK3401Board.h | 9 +++++---- variants/rak3401/variant.h | 11 ++++++++--- 3 files changed, 41 insertions(+), 12 deletions(-) diff --git a/variants/rak3401/RAK3401Board.cpp b/variants/rak3401/RAK3401Board.cpp index b9431c92..e2a9f318 100644 --- a/variants/rak3401/RAK3401Board.cpp +++ b/variants/rak3401/RAK3401Board.cpp @@ -23,10 +23,33 @@ void RAK3401Board::begin() { pinMode(PIN_3V3_EN, OUTPUT); digitalWrite(PIN_3V3_EN, HIGH); -#ifdef P_LORA_PA_EN - // Initialize RAK13302 1W LoRa transceiver module PA control pin + // Initialize SKY66122-11 FEM on the RAK13302 module. + // CSD (P0.24) and CPS (P0.21) must be HIGH for both TX and RX modes. + // CTX (P0.31) selects TX(HIGH) vs RX(LOW) and also enables the 5V boost + // converter that powers the PA section (VCC1/VCC2). + // The LNA section (VSUP1/VCC0) runs on 3.3V and works with boost off. + pinMode(P_LORA_PA_CSD, OUTPUT); + digitalWrite(P_LORA_PA_CSD, HIGH); // CSD=1: enable FEM + + pinMode(SX126X_POWER_EN, OUTPUT); + digitalWrite(SX126X_POWER_EN, HIGH); // CPS=1: enable TX/RX paths + pinMode(P_LORA_PA_EN, OUTPUT); - digitalWrite(P_LORA_PA_EN, LOW); // Start with PA disabled - delay(10); // Allow PA module to initialize + digitalWrite(P_LORA_PA_EN, LOW); // CTX=0: RX mode, boost off + + delay(1); // SKY66122 turn-on settling time +} + +#ifdef NRF52_POWER_MANAGEMENT +void RAK3401Board::initiateShutdown(uint8_t reason) { + // Put SKY66122 in guaranteed <1 uA shutdown (Mode 4: CSD=0, CTX=0, CPS=0) + digitalWrite(P_LORA_PA_EN, LOW); // CTX=0, boost off + digitalWrite(SX126X_POWER_EN, LOW); // CPS=0 + digitalWrite(P_LORA_PA_CSD, LOW); // CSD=0 + + // Disable 3V3 switched peripherals + digitalWrite(PIN_3V3_EN, LOW); + + enterSystemOff(reason); +} #endif -} \ No newline at end of file diff --git a/variants/rak3401/RAK3401Board.h b/variants/rak3401/RAK3401Board.h index 20edf906..8ca5b52e 100644 --- a/variants/rak3401/RAK3401Board.h +++ b/variants/rak3401/RAK3401Board.h @@ -38,13 +38,14 @@ public: return "RAK 3401"; } -#ifdef P_LORA_PA_EN + // SKY66122 FEM TX/RX switching via CTX pin. + // CTX=HIGH: TX mode + 5V boost ON (PA powered from VCC1/VCC2) + // CTX=LOW: RX mode + 5V boost OFF (LNA powered from VSUP1 at 3.3V) void onBeforeTransmit() override { - digitalWrite(P_LORA_PA_EN, HIGH); // Enable PA before transmission + digitalWrite(P_LORA_PA_EN, HIGH); // CTX=1: TX mode, boost on } void onAfterTransmit() override { - digitalWrite(P_LORA_PA_EN, LOW); // Disable PA after transmission to save power + digitalWrite(P_LORA_PA_EN, LOW); // CTX=0: RX mode, boost off } -#endif }; diff --git a/variants/rak3401/variant.h b/variants/rak3401/variant.h index 56fe0816..f2ef4ace 100644 --- a/variants/rak3401/variant.h +++ b/variants/rak3401/variant.h @@ -147,8 +147,14 @@ 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 pins (active HIGH, active LOW = shutdown <1uA) +// CSD+CPS must be HIGH for TX and RX; CTX selects TX(HIGH) vs RX(LOW) +// CTX also enables the 5V boost converter for the PA during TX +#define P_LORA_PA_CSD (24) // P0.24 -> SKY66122 CSD (pin 11) - FEM enable +#define SX126X_POWER_EN (21) // P0.21 -> SKY66122 CPS (pin 1) - path select +#define P_LORA_PA_EN (31) // P0.31 -> SKY66122 CTX (pin 2) - TX/RX + boost EN + +// DIO2 has a NC 0R footprint (R25) to CTX; not connected by default #define SX126X_DIO2_AS_RF_SWITCH #define SX126X_DIO3_TCXO_VOLTAGE 1.8 @@ -159,7 +165,6 @@ 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