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cpu/nrf5x_common: fix ztimer issue on warm-boot #20665

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merged 1 commit into from
May 13, 2024
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cpu/nrf5x_common: fix ztimer issue on warm-boot #20665

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12 changes: 11 additions & 1 deletion cpu/nrf5x_common/clock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -78,10 +78,18 @@
irq_restore(state);
}

/**
* True if the low frequency clock (LFCLK) has been started by RIOT.
* We don't rely on NRF_CLOCK->LFCLKSTAT since that register appears to be latched
* for a short amount of time after a soft reset on at least nRF52832 and nRF52840.
* @see https://devzone.nordicsemi.com/f/nordic-q-a/35792/nrf_clock--lfclkstat-register-contents-are-not-properly-evaluated-after-a-system-reset-if-rtc-compare-event-1-or-2-are-used/138995

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*/
static bool clock_lf_running = false;

void clock_start_lf(void)
{
/* abort if LF clock is already running */
if (NRF_CLOCK->LFCLKSTAT & CLOCK_LFCLKSTAT_STATE_Msk) {
if (clock_lf_running) {
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Is there a case where this function would be called more than once anyway?
I think we could easily drop that check.

It's only called in rtt_init() which is run once, the call in nimble_riot.c could be guarded with a if (!IS_USED(MODULE_PERIPH_RTT))

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Moving this check to a guard in nimble_riot.c moves logic to somewhere where it doesn't belong to. And the product specification explicitly mentions that changing clock parameters while the clock is running is not allowed.

return;
}

Expand All @@ -92,6 +100,7 @@
NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
NRF_CLOCK->TASKS_LFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {}
clock_lf_running = true;

/* calibrate the RC LF clock if applicable */
#if (CLOCK_HFCLK && (CLOCK_LFCLK == 0))
Expand All @@ -105,4 +114,5 @@
{
NRF_CLOCK->TASKS_LFCLKSTOP = 1;
while (NRF_CLOCK->LFCLKSTAT & CLOCK_LFCLKSTAT_STATE_Msk) {}
clock_lf_running = false;
}
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