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nRF52 BLE: wait for LFXO crystal before enabling SoftDevice (fixes t1000e hanging at reboot) #1939

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nRF52 BLE: wait for LFXO crystal before enabling SoftDevice (fixes t1000e hanging at reboot) #1939

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nRF52 BLE: wait for LFXO crystal before enabling SoftDevice
weebl2000 Mar 6, 2026
e715a4b
Check if we use LFXO and guard with 2 second timeout for broken crystals
weebl2000 Mar 6, 2026
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18 changes: 18 additions & 0 deletions src/helpers/nrf52/SerialBLEInterface.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,24 @@ void SerialBLEInterface::begin(const char* prefix, char* name, uint32_t pin_code
char charpin[20];
snprintf(charpin, sizeof(charpin), "%lu", (unsigned long)pin_code);

// Ensure LFXO crystal is fully started before enabling SoftDevice.
// The framework starts LFXO in init() but doesn't wait for it.
// On fast boots (filesystem already formatted), Bluefruit.begin() can
// be called before the crystal is stable, hanging sd_softdevice_enable().
// See: https://github.com/meshcore-dev/MeshCore/issues/1780
#ifdef USE_LFXO
{
uint32_t lfclk_start = millis();
while (!NRF_CLOCK->EVENTS_LFCLKSTARTED) {
if (millis() - lfclk_start >= 2000) {
Serial.println("WARNING: LFXO crystal did not start within 2s — check 32.768kHz crystal");
break;
}
delay(1);
}
}
#endif

// If we want to control BLE LED ourselves, uncomment this:
// Bluefruit.autoConnLed(false);
Bluefruit.configPrphBandwidth(BANDWIDTH_MAX);
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