Using PPI to enable/disable HFCLK

RE: Using PPI to enable/disable HFCLK

Stefan Birnir Sverrisson — Tue, 18 Aug 2015 17:14:46 GMT

Yes, you are correct. Thank you for the correction. I have edited my answer to correct myself.

RE: Using PPI to enable/disable HFCLK

FormerMember — Fri, 14 Aug 2015 14:52:10 GMT

Stefan, I thought the SET and CLR (CHENSET) registers in peripherals are for avoiding doing the operation that you mentioned?

RE: Using PPI to enable/disable HFCLK

shyam — Fri, 14 Aug 2015 14:28:27 GMT

Hi Stephan

I tried your suggestion. See below. This code doesn't work. It asserts in the end (last line).

==========

ASSERT(((NRF_CLOCK->HFCLKSTAT & CLOCK_HFCLKSTAT_STATE_Msk) == (CLOCK_HFCLKSTAT_STATE_NotRunning << CLOCK_HFCLKSTAT_STATE_Pos) ) || \
               ((NRF_CLOCK->HFCLKSTAT & CLOCK_HFCLKSTAT_SRC_Msk) == (CLOCK_HFCLKSTAT_SRC_RC << CLOCK_HFCLKSTAT_SRC_Pos))); /* ensure clock is stopped */

NRF_RTC0->INTENCLR = RTC_INTENCLR_COMPARE1_Msk;
NRF_RTC0->EVTENCLR = RTC_EVTENCLR_COMPARE1_Msk;
NRF_PPI->CH[9].EEP = (uint32_t) &NRF_RTC0->EVENTS_COMPARE[1];
NRF_PPI->CH[9].TEP = (uint32_t) &NRF_CLOCK->TASKS_HFCLKSTART;
NRF_PPI->CHENSET |= PPI_CHENSET_CH9_Msk;
#define TEST_TICKS (3)
#define TICKS_TO_US(ticks) ((uint64_t)ticks*(uint64_t)1000000/32768)
NRF_RTC0->CC[1] = NRF_RTC0->COUNTER + TEST_TICKS;
nrf_delay_us(TICKS_TO_US(TEST_TICKS)); /* wait until RTC fires TEST_TICKS */
nrf_delay_us(TICKS_TO_US(TEST_TICKS)); /* a little extra wait to make sure */
nrf_delay_ms(2); /* Wait 1 ms of warmup time and an extra 1 ms to make sure */
ASSERT(((NRF_CLOCK->HFCLKSTAT & CLOCK_HFCLKSTAT_STATE_Msk) == (CLOCK_HFCLKSTAT_STATE_Running << CLOCK_HFCLKSTAT_STATE_Pos) ) && \
             ((NRF_CLOCK->HFCLKSTAT & CLOCK_HFCLKSTAT_SRC_Msk) == (CLOCK_HFCLKSTAT_SRC_Xtal << CLOCK_HFCLKSTAT_SRC_Pos)));

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RE: Using PPI to enable/disable HFCLK

Stefan Birnir Sverrisson — Fri, 14 Aug 2015 11:39:01 GMT

Hi shyam

Your assumption is correct, shortcuts are only to use within the same peripheral. With PPI, you can connect an event of one peripheral with a task of another peripheral.

There should be no problem with using PPI to stop the 16MHz crystal. The PPI does not need the 16MHz crystal, it only needs 16MHz RC. The RTC uses either 32kHz RC or crystal.

You can see peripheral resource dependency in table 33 in nRF51822_PS v3.1. The PPI is not listed in this table, but it uses 16MHz RC.

Update 18.8.2015 I have attached a code below to show how this is possible

rtc0_triggering_HFLCK_start_and_stop_via_ppi.zip