Implement 'agc' reset for SX126x chip family

There's no actual agc on SX126x chips but you can reset the analog
registers by doing a warm sleep & running calibration.

Author: Wessel Nieboer

src/main.cpp

@@ -1125,6 +1125,13 @@ void loop()
             lastRadioMissedIrqPoll = millis();
             RadioLibInterface::instance->pollMissedIrqs();
         }
+
+        // Periodic AGC reset — warm sleep + recalibrate to prevent stuck AGC gain
+        static uint32_t lastAgcReset;
+        if (!Throttle::isWithinTimespanMs(lastAgcReset, AGC_RESET_INTERVAL_MS)) {
+            lastAgcReset = millis();
+            RadioLibInterface::instance->resetAGC();
+        }
     }
 
 #ifdef DEBUG_STACK

src/mesh/RadioLibInterface.cpp

@@ -529,6 +529,11 @@ void RadioLibInterface::pollMissedIrqs()
     }
 }
 
+void RadioLibInterface::resetAGC()
+{
+    // Base implementation: no-op. Override in chip-specific subclasses.
+}
+
 void RadioLibInterface::checkRxDoneIrqFlag()
 {
     if (iface->checkIrq(RADIOLIB_IRQ_RX_DONE)) {

src/mesh/RadioLibInterface.h

@@ -19,6 +19,8 @@
 // In addition to the default Rx flags, we need the PREAMBLE_DETECTED flag to detect whether we are actively receiving
 #define MESHTASTIC_RADIOLIB_IRQ_RX_FLAGS (RADIOLIB_IRQ_RX_DEFAULT_FLAGS | (1 << RADIOLIB_IRQ_PREAMBLE_DETECTED))
 
+#define AGC_RESET_INTERVAL_MS (60 * 1000) // 60 seconds
+
 /**
  * We need to override the RadioLib ArduinoHal class to add mutex protection for SPI bus access
  */
@@ -117,6 +119,13 @@ class RadioLibInterface : public RadioInterface, protected concurrency::Notified
      */
     void pollMissedIrqs();
 
+    /**
+     * Reset AGC by power-cycling the analog frontend.
+     * Subclasses override with chip-specific calibration sequences.
+     * Safe to call periodically — skips if currently sending or receiving.
+     */
+    virtual void resetAGC();
+
     /**
      * Debugging counts
      */

src/mesh/SX126xInterface.cpp

@@ -434,6 +434,51 @@ template <typename T> bool SX126xInterface<T>::sleep()
     return true;
 }
 
+template <typename T> void SX126xInterface<T>::resetAGC()
+{
+    // Safety: don't reset mid-packet
+    if (sendingPacket != NULL || (isReceiving && isActivelyReceiving()))
+        return;
+
+    LOG_INFO("SX126x AGC reset: warm sleep + Calibrate(0x7F)");
+
+    // 1. Warm sleep — powers down the entire analog frontend, resetting AGC state.
+    //    A plain standby→startReceive cycle does NOT reset the AGC.
+    lora.sleep(true);
+
+    // 2. Wake to RC standby for stable calibration
+    lora.standby(RADIOLIB_SX126X_STANDBY_RC, true);
+
+    // 3. Calibrate all blocks (ADC, PLL, image, RC oscillators)
+    uint8_t calData = RADIOLIB_SX126X_CALIBRATE_ALL;
+    module.SPIwriteStream(RADIOLIB_SX126X_CMD_CALIBRATE, &calData, 1, true, false);
+
+    // 4. Wait for calibration to complete (BUSY pin goes low)
+    module.hal->delay(5);
+    uint32_t start = millis();
+    while (module.hal->digitalRead(module.getGpio())) {
+        if (millis() - start > 50)
+            break;
+        module.hal->yield();
+    }
+
+    // 5. Re-apply settings that calibration may have reset
+
+    // DIO2 as RF switch
+#ifdef SX126X_DIO2_AS_RF_SWITCH
+    lora.setDio2AsRfSwitch(true);
+#elif defined(ARCH_PORTDUINO)
+    if (portduino_config.dio2_as_rf_switch)
+        lora.setDio2AsRfSwitch(true);
+#endif
+
+    // RX boosted gain mode
+    lora.setRxBoostedGainMode(config.lora.sx126x_rx_boosted_gain);
+
+    // 6. Resume receiving
+    startReceive();
+}
+
 /** Control PA mode for GC1109 FEM - CPS pin selects full PA (txon=true) or bypass mode (txon=false) */
 template <typename T> void SX126xInterface<T>::setTransmitEnable(bool txon)
 {

src/mesh/SX126xInterface.h

@@ -28,6 +28,8 @@ template <class T> class SX126xInterface : public RadioLibInterface
 
     bool isIRQPending() override { return lora.getIrqFlags() != 0; }
 
+    void resetAGC() override;
+
     void setTCXOVoltage(float voltage) { tcxoVoltage = voltage; }
 
   protected: