Questions about the temperature sensor (TEMP)

[backstreet.devisor]

Hi.

I am experimenting with an internal temperature sensor (TEMP) on an nRF52810 microcontroller and have some questions: 

1. How to select a crystal oscillator as a source of HFCLK to achieve better temperature sensor performance?

2. How to measure the time (in microseconds) in which the microcontroller completes the temperature measurement (the time between TASKS_START and DATARDY)? 

Thanks.

[Håkon Alseth]

Hi,

 

You are not clearing your events, and it seems that you're also not dereferencing TEMP_EVENTS_DATARDY. The data types are returned as 64 bit length, so you need to print as "%lld" types.

I would recommend that you rather include "nrf.h" and access the temp directly (or include nrf_temp.h and use that API):

/*
 * Copyright (c) 2016 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <zephyr/zephyr.h>
#include <zephyr/drivers/gpio.h>
#include <zephyr/timing/timing.h>
#include "nrf.h"

int main(void)
{
	int32_t tmp;
	timing_t start_time, end_time;
	uint64_t total_cycles;
	uint64_t total_ns;
	timing_init();
	while (1) {
		timing_start();
		NRF_TEMP->TASKS_START = 1;
		start_time = timing_counter_get();
		while (NRF_TEMP->EVENTS_DATARDY == 0) {}
		end_time = timing_counter_get();
		timing_stop();		
		NRF_TEMP->EVENTS_DATARDY = 0;
		printk("Temperature measurement time = %lld ns\n", timing_cycles_to_ns(timing_cycles_get(&start_time, &end_time)));
		tmp = (int32_t)NRF_TEMP->TEMP / 4;
		printk("SoC temperature = %d\n", tmp);
		NRF_TEMP->TASKS_STOP = 1;
		k_msleep(5000);
	}
	return 0;
}

 

This will print approx. 35 us:

Temperature measurement time = 35437 ns

 

Kind regards,

Håkon

[backstreet.devisor]

Hi Håkon. Thank you for your reply.

Yeah, your advice worked. When I include "nrf.h" I get the temperature calculation in 35 ns.

Could you please answer my first question. How can I select an external generator as HFCLK and be sure that the temperature measurement performance will improve?

Thanks.

[Håkon Alseth]

Either use clock_control module (recommended approach, as other modules might also request HFCLK):

https://github.com/nrfconnect/sdk-nrf/blob/v2.5.0/samples/cellular/at_client/src/main.c#L16-L24

 

Or, you can directly start it via the registers:

NRF_CLOCK->TASKS_HFCLKSTART = 1;

while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);

NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

 

Kind regards,

Håkon

[backstreet.devisor]

Thank you.