nRF9160 HFINT accuracy problem.

[bbslhb]

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]

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\n");
		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

[bbslhb]

“There's an HFXO in the nRF9160 SIP, which is used by the modem for the radio communication etc.”

So can I use HFXO as crystal source for nRF9160 "LTE_BLE_GATEWAY" 1M baud rate?

Or HFXO can only be used by modem?

NRF_CLOCK->TASKS_HFCLKSTART=1 only use HFCLK but not defined HFINT or HFXO.

Both HFINT and HFXO can be the source of HFCLK.

[Håkon Alseth]

bbslhb said:

So can I use HFXO as crystal source for nRF9160 "LTE_BLE_GATEWAY" 1M baud rate?

Yes, you can use that as a HFCLK source. By default you use the HFINT, but by issuing TASKS_HFCLKSTART, you start up the HFXO.

 

bbslhb said:

Or HFXO can only be used by modem?

It can be used by the application as well. Just start it using NRF_CLOCK->TASKS_HFCLKSTART and wait for it to start up (approx. 1 ms) 

You can check the HFCLKSTAT register to see which is running.

 

Kind regards,

Håkon