nRF9160 HFINT accuracy problem.

Question

Hello, dear sir: 
 In my opinion, HFXO means external oscillator, I need to buy a external oscillator because it is not exist in nRF9160? 
 HFINT means internal oscillator, I don't need to buy a external oscillator because it is in nRF9160 already? 
 
 There is a schematic in nRF9160_ps_v1.1.pdf which didn't use HFXO as a reference design. 
 HFINT accuracy is 1% and HFXO accuracy is 1ppm. 
 So will the HFINT accuracy cause problem if I run lte_ble_gateway on nRF9160 and hci_uart on nRF52840 in nRF9160DK platform because the default HCI baud rate is 1M? 
 HFINT accuracy is badly affected by temperature. 
 So how to solve the problem if HCI_uart with 1M communication is affected by low accuracy HFINT?

Håkon Alseth · Accepted Answer

Hi, 
 
 There's an HFXO in the nRF9160 SIP, which is used by the modem for the radio communication etc. 
 If you want to start the HFCLK, the simplest form is NRF_CLOCK->TASKS_HFCLKSTART=1;, then wait and clear the EVENTS_HFCLKSTARTED event. 
 To use the clock subsys, you can do it similar to this: https://github.com/nrfconnect/sdk-nrf/blob/master/samples/bluetooth/direct_test_mode/src/dtm.c#L462-L479 
 static int clock_init(void)
{
	int err;
	const struct device *clock;

	clock = device_get_binding("CLOCK");
	if (!clock) {
 printk("Unable to find clock device binding
");
 return -ENODEV;
	}

	err = clock_control_on(clock, CLOCK_CONTROL_NRF_SUBSYS_HF);
	if (err) {
 printk("Unable to turn on the clock: %d", err);
	}

	return err;
} 
 
 So will the HFINT accuracy cause problem if I run lte_ble_gateway on nRF9160 and hci_uart on nRF52840 in nRF9160DK platform because the default HCI baud rate is 1M? 
 It can, especially for larger transmission (due to drift), as the max. tolerance is given to 5%: https://infocenter.nordicsemi.com/topic/ps_nrf9160/pmu_oscillators.html?cp=2_0_0_4_0_3_3#unique_847745536 
 
 Kind regards, 
 Håkon

nRF9160 HFINT accuracy problem.

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