nRF5340 with RV3028C7 external clock EVENTS_LFCLKSTARTED not triggering

[denis]

Our design has an nRF5340 with RV3028C7 to provide the 32 kHz clock via P0.00.

If I configure P0.00 as a digital input, I can see the pin toggling.

However, if I use the code below to try and switch from to the external clock, the EVENTS_LFCLKSTARTED doesn't happen.  Any idea why this would be?

NRF_CLOCK->LFCLKSRC = CLOCK_LFCLKSRC_SRC_LFXO << CLOCK_LFCLKSRC_SRC_Pos;

NRF_OSCILLATORS->XOSC32KI.INTCAP = OSCILLATORS_XOSC32KI_INTCAP_INTCAP_External << OSCILLATORS_XOSC32KI_INTCAP_INTCAP_Pos;

NRF_OSCILLATORS->XOSC32KI.BYPASS = OSCILLATORS_XOSC32KI_BYPASS_BYPASS_Enabled << OSCILLATORS_XOSC32KI_BYPASS_BYPASS_Pos;

NRF_P0->PIN_CNF[0] = GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos |

GPIO_PIN_CNF_DRIVE_S0S1 << GPIO_PIN_CNF_DRIVE_Pos |

GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos |

GPIO_PIN_CNF_INPUT_Disconnect << GPIO_PIN_CNF_INPUT_Pos;

NRF_P0->PIN_CNF[1] = GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos |

GPIO_PIN_CNF_DRIVE_S0S1 << GPIO_PIN_CNF_DRIVE_Pos |

GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos |

GPIO_PIN_CNF_INPUT_Disconnect<< GPIO_PIN_CNF_INPUT_Pos;

NRF_CLOCK->LFCLKALWAYSRUN = CLOCK_LFCLKALWAYSRUN_ALWAYSRUN_AlwaysRun << CLOCK_LFCLKALWAYSRUN_ALWAYSRUN_Pos;

NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;

NRF_CLOCK->TASKS_LFCLKSTART = 1;

uint32_t count = 0;

while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {

// wait for LFCLK to start

++count;

}