Clock inaccuracy of nRF52832 custom board

[barky]

When using uart example on my curstom board, from /examples/peripheral/uart ,at baudrate 9600, bits are read with a little offset - so that starting from 4th bit, it is mistaken with the fallowing bit.

When measuring with logic analyzer, lenght of each bit is 92us, but it should be 104us at this baudrate.

The function nrf_delay_ms(100) gives a delay of 88.67ms.

I have solderd both 32MHz and 32.768KHz crystals on board, but for this example i am pretty sure i am using internal clock.

Any suggestions? Thanks

[Kenneth]

Hi, have you started the external crystal oscillator by calling NRF_CLOCK->TASKS_HFCLKSTART = 1;?

http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/clock.html?cp=2_1_0_18_2#topic 

[barky]

Thanks you for the tip.

Problem stays the same. I tried to measure the waveform on 32MHz crystal, but all i see on osciloscope is 100mV DC on both X1 and X2 pins.

[AmbystomaLabs]

You can never measure clock at a crystal with probes.  The probes will always load pull the crystal. The easiest way to measure frequency accuracy is with a calibrated spectrum analyzer with the nRF producing CW. Also you can route P_Clk out through gpio and measure that.

[barky]

Well yes, the frequency will shift, because of the probe capacitance, but waveform should have been visible.

I will continue actively debugging the clock. I added lines to code, but program halts, meaning that it is stuck in a while loop:

// Start the external high frequency crystal

NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

NRF_CLOCK->TASKS_HFCLKSTART = 1;

nrf_clock_lf_actv_src_get();

// Wait for the external oscillator to start up

while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);

Isn't it needed to set the clock frequency e.g. 32MHz or 16MHz somewhere?

[Kenneth]

No need to set the frequency, as there is only one crystal supported (32MHz).

Does the radio work? Are you able to transmit and receive data.