Fix rak4631 boot with DC/DC

src/helpers/NRF52Board.cpp

@@ -130,10 +130,17 @@ bool NRF52Board::checkBootVoltage(const PowerMgtConfig* config) {
   // Only trigger shutdown if reading is valid (>1000mV) AND below threshold
   // This prevents spurious shutdowns on ADC glitches or uninitialized reads
   if (boot_voltage_mv > 1000 && boot_voltage_mv < config->voltage_bootlock) {
-    MESH_DEBUG_PRINTLN("PWRMGT: Boot voltage too low - entering protective shutdown");
+    // First reading below threshold - wait for DCDC to stabilize and re-read
+    delay(50);
+    boot_voltage_mv = getBattMilliVolts();
+    MESH_DEBUG_PRINTLN("PWRMGT: Boot voltage (confirmed) = %u mV (threshold = %u mV)",
+        boot_voltage_mv, config->voltage_bootlock);
 
-    initiateShutdown(SHUTDOWN_REASON_BOOT_PROTECT);
-    return false;  // Should never reach this
+    if (boot_voltage_mv > 1000 && boot_voltage_mv < config->voltage_bootlock) {
+      MESH_DEBUG_PRINTLN("PWRMGT: Boot voltage too low - entering protective shutdown");
+      initiateShutdown(SHUTDOWN_REASON_BOOT_PROTECT);
+      return false;  // Should never reach this
+    }
   }
 
   return true;
@@ -177,7 +184,7 @@ void NRF52Board::enterSystemOff(uint8_t reason) {
   NVIC_SystemReset();
 }
 
-void NRF52Board::configureVoltageWake(uint8_t ain_channel, uint8_t refsel) {
+bool NRF52Board::configureVoltageWake(uint8_t ain_channel, uint8_t refsel) {
   // LPCOMP is not managed by SoftDevice - direct register access required
   // Halt and disable before reconfiguration
   NRF_LPCOMP->TASKS_STOP = 1;
@@ -213,6 +220,14 @@ void NRF52Board::configureVoltageWake(uint8_t ain_channel, uint8_t refsel) {
     delayMicroseconds(50);
   }
 
+  // Safety: if voltage is already above threshold, UP detection will never fire
+  if (NRF_LPCOMP->RESULT & LPCOMP_RESULT_RESULT_Msk) {
+    MESH_DEBUG_PRINTLN("PWRMGT: LPCOMP shows voltage above threshold - unsafe for SYSTEMOFF");
+    NRF_LPCOMP->TASKS_STOP = 1;
+    NRF_LPCOMP->ENABLE = LPCOMP_ENABLE_ENABLE_Disabled;
+    return false;
+  }
+
   if (refsel == 7) {
     MESH_DEBUG_PRINTLN("PWRMGT: LPCOMP wake configured (AIN%d, ref=ARef)", ain_channel);
   } else if (refsel <= 6) {
@@ -235,19 +250,23 @@ void NRF52Board::configureVoltageWake(uint8_t ain_channel, uint8_t refsel) {
   }
 
   MESH_DEBUG_PRINTLN("PWRMGT: VBUS wake configured");
+
+  return true;
 }
 #endif
 
 void NRF52BoardDCDC::begin() {
   NRF52Board::begin();
 
-  // Enable DC/DC converter for improved power efficiency
+  // Enable DC/DC converter only when SoftDevice is managing the POWER peripheral.
+  // Without SoftDevice, NRF_POWER->DCDCEN = 1 leaves the DC/DC permanently on,
+  // which causes boot failures on some boards when running on battery alone.
+  // The SoftDevice manages DC/DC dynamically (on during radio, off during idle),
+  // which is the safe way to use it.
   uint8_t sd_enabled = 0;
   sd_softdevice_is_enabled(&sd_enabled);
   if (sd_enabled) {
     sd_power_dcdc_mode_set(NRF_POWER_DCDC_ENABLE);
-  } else {
-    NRF_POWER->DCDCEN = 1;
   }
 }
 

src/helpers/NRF52Board.h

@@ -40,7 +40,7 @@ class NRF52Board : public mesh::MainBoard {
 
   bool checkBootVoltage(const PowerMgtConfig* config);
   void enterSystemOff(uint8_t reason);
-  void configureVoltageWake(uint8_t ain_channel, uint8_t refsel);
+  bool configureVoltageWake(uint8_t ain_channel, uint8_t refsel);
   virtual void initiateShutdown(uint8_t reason);
 #endif
 

variants/heltec_t114/T114Board.cpp

@@ -25,7 +25,9 @@ void T114Board::initiateShutdown(uint8_t reason) {
   digitalWrite(PIN_BAT_CTL, enable_lpcomp ? HIGH : LOW);
 
   if (enable_lpcomp) {
-    configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel);
+    if (!configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel)) {
+      NVIC_SystemReset();
+    }
   }
 
   enterSystemOff(reason);

variants/rak4631/RAK4631Board.cpp

@@ -3,6 +3,22 @@
 
 #include "RAK4631Board.h"
 
+#ifdef BOOT_DIAG
+// Diagnostic LED blink: N short blinks on green LED to indicate boot stage
+static void diag_blink(uint8_t count) {
+  pinMode(PIN_LED1, OUTPUT);
+  for (uint8_t i = 0; i < count; i++) {
+    digitalWrite(PIN_LED1, HIGH);
+    delay(100);
+    digitalWrite(PIN_LED1, LOW);
+    delay(150);
+  }
+  delay(300);
+}
+#else
+#define diag_blink(n) ((void)0)
+#endif
+
 #ifdef NRF52_POWER_MANAGEMENT
 // Static configuration for power management
 // Values set in variant.h defines
@@ -18,15 +34,26 @@ void RAK4631Board::initiateShutdown(uint8_t reason) {
 
   if (reason == SHUTDOWN_REASON_LOW_VOLTAGE ||
       reason == SHUTDOWN_REASON_BOOT_PROTECT) {
-    configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel);
+    if (!configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel)) {
+      NVIC_SystemReset();
+    }
   }
 
   enterSystemOff(reason);
 }
 #endif // NRF52_POWER_MANAGEMENT
 
 void RAK4631Board::begin() {
+  diag_blink(1);  // Stage 1: entering begin()
+
+#ifdef DISABLE_DCDC
+  NRF52Board::begin();
+#else
   NRF52BoardDCDC::begin();
+#endif
+
+  diag_blink(2);  // Stage 2: board base init done
+
   pinMode(PIN_VBAT_READ, INPUT);
 #ifdef PIN_USER_BTN
   pinMode(PIN_USER_BTN, INPUT_PULLUP);
@@ -42,12 +69,19 @@ void RAK4631Board::begin() {
 
   Wire.begin();
 
+  diag_blink(3);  // Stage 3: I2C done, about to configure LoRa power
+
   pinMode(SX126X_POWER_EN, OUTPUT);
-#ifdef NRF52_POWER_MANAGEMENT
+#if defined(NRF52_POWER_MANAGEMENT) && !defined(DISABLE_BOOT_PROTECTION)
   // Boot voltage protection check (may not return if voltage too low)
   // We need to call this after we configure SX126X_POWER_EN as output but before we pull high
   checkBootVoltage(&power_config);
 #endif
+
+  diag_blink(4);  // Stage 4: power check passed
+
   digitalWrite(SX126X_POWER_EN, HIGH);
   delay(10);   // give sx1262 some time to power up
+
+  diag_blink(5);  // Stage 5: board.begin() complete
 }

variants/rak4631/platformio.ini

@@ -48,6 +48,23 @@ build_src_filter = ${rak4631.build_src_filter}
   +<helpers/ui/SSD1306Display.cpp>
   +<../examples/simple_repeater>
 
+; Diagnostic build: LED blinks at boot stages + boot protection disabled
+[env:RAK_4631_repeater_diag]
+extends = env:RAK_4631_repeater
+build_flags =
+  ${env:RAK_4631_repeater.build_flags}
+  -D BOOT_DIAG
+  -D DISABLE_BOOT_PROTECTION
+
+; Diagnostic build: LED blinks + boot protection disabled + DC/DC disabled
+[env:RAK_4631_repeater_diag_no_dcdc]
+extends = env:RAK_4631_repeater
+build_flags =
+  ${env:RAK_4631_repeater.build_flags}
+  -D BOOT_DIAG
+  -D DISABLE_BOOT_PROTECTION
+  -D DISABLE_DCDC
+
 [env:RAK_4631_repeater_bridge_rs232_serial1]
 extends = rak4631
 build_flags =

variants/xiao_nrf52/XiaoNrf52Board.cpp

@@ -22,7 +22,9 @@ void XiaoNrf52Board::initiateShutdown(uint8_t reason) {
   digitalWrite(VBAT_ENABLE, enable_lpcomp ? LOW : HIGH);
 
   if (enable_lpcomp) {
-    configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel);
+    if (!configureVoltageWake(power_config.lpcomp_ain_channel, power_config.lpcomp_refsel)) {
+      NVIC_SystemReset();
+    }
   }
 
   enterSystemOff(reason);