RE: nrf52 WDT LFCLK sourcing

bjorn-spockeli — Fri, 30 Aug 2019 13:51:01 GMT

[quote user=""][/quote]

Does "the watchdog will automatically force the 32.768 kHz RC oscillator on as long as no other 32.768 kHz clock source is running" mean 'the internal RC will be used to clock the WDT only, until you configure LFCLKSRC to be something else and trigger TASKS_LFCLKSTART, at which point LFCLK will be used to drive the WDT'?

The LFCLK can have two sources, the internal RC oscillator (LFRC)or an external crystal oscillator (LFXO). If you have nRF52 design without the external crystal, then the LFRC will be used to clock all peripherals that are active and requesting the LFCLK.

If its a design with an external crystal and that is configured as the LFCLK source, but no other peripheral is using the LFCLK, then the WDT will use the LFRC and not the LFXO. If a peripheral requests the LFCLK, then the LFXO will start and that will be the LF clock source for both the WDT and the peripheral.

[quote user=""]Does the LFCLK source persist across a soft reset when the WDT forces it to stay active, or does it revert to using the internal RC?[/quote]

As the CLOCK is a peripheral and a SoftReset will reset the Peripheral registers, then I beleive that the LFCLK will revert to the RC configuration post a SoftReset.

Best regards

Bjørn