RE: ADC Peripheral Power Management on NRF52840 (BMD-340)

Einar Thorsrud — Tue, 04 Mar 2025 09:39:21 GMT

Hi,

I am sorry for the very late reply. You are right, when using the Zephyr blocking API there is no stop. It is also not needed in this case, and you only need to enable device power management in Kconfig, and it will be handled automatically under the holld. That can be demonstrated by using the adc_dt sample from SDK 2.9, with this added to prj.conf:

CONFIG_PM_DEVICE=y
CONFIG_PM_DEVICE_RUNTIME=y

However, the sample will continue to consume a significant amount of current in sleep due to the UART being enabled, so I modified the sample like this to sample for a short time and then also disable the UART. If you measure the current consumption of this, you should see a low sleep current as expected:

/*
 * Copyright (c) 2020 Libre Solar Technologies GmbH
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <inttypes.h>
#include <stddef.h>
#include <stdint.h>

#include <zephyr/device.h>
#include <zephyr/devicetree.h>
#include <zephyr/drivers/adc.h>
#include <zephyr/kernel.h>
#include <zephyr/sys/printk.h>
#include <zephyr/sys/util.h>
#include <zephyr/pm/device.h>
#include <zephyr/pm/device_runtime.h>

#if !DT_NODE_EXISTS(DT_PATH(zephyr_user)) || \
	!DT_NODE_HAS_PROP(DT_PATH(zephyr_user), io_channels)
#error "No suitable devicetree overlay specified"
#endif

#define DT_SPEC_AND_COMMA(node_id, prop, idx) \
	ADC_DT_SPEC_GET_BY_IDX(node_id, idx),

/* Data of ADC io-channels specified in devicetree. */
static const struct adc_dt_spec adc_channels[] = {
	DT_FOREACH_PROP_ELEM(DT_PATH(zephyr_user), io_channels,
			     DT_SPEC_AND_COMMA)
};

void uart_suspend(void)
{
	static const struct device *const console_dev = DEVICE_DT_GET(DT_CHOSEN(zephyr_console));

	/* Disable console UART */
	int err = pm_device_action_run(console_dev, PM_DEVICE_ACTION_SUSPEND);
	if (err < 0)
	{
		printk("Unable to suspend console UART. (err: %d)\n", err);
	}
}

int main(void)
{
	int err;
	uint32_t count = 0;
	uint16_t buf;
	struct adc_sequence sequence = {
		.buffer = &buf,
		/* buffer size in bytes, not number of samples */
		.buffer_size = sizeof(buf),
	};
	/* Configure channels individually prior to sampling. */
	for (size_t i = 0U; i < ARRAY_SIZE(adc_channels); i++) {
		if (!adc_is_ready_dt(&adc_channels[i])) {
			printk("ADC controller device %s not ready\n", adc_channels[i].dev->name);
			return 0;
		}

		err = adc_channel_setup_dt(&adc_channels[i]);
		if (err < 0) {
			printk("Could not setup channel #%d (%d)\n", i, err);
			return 0;
		}
	}

	for (int k = 0; k < 2; k++) {
		printk("ADC reading[%u]:\n", count++);
		for (size_t i = 0U; i < ARRAY_SIZE(adc_channels); i++) {
			int32_t val_mv;

			printk("- %s, channel %d: ",
			       adc_channels[i].dev->name,
			       adc_channels[i].channel_id);

			(void)adc_sequence_init_dt(&adc_channels[i], &sequence);

			err = adc_read_dt(&adc_channels[i], &sequence);
			if (err < 0) {
				printk("Could not read (%d)\n", err);
				continue;
			}

			/*
			 * If using differential mode, the 16 bit value
			 * in the ADC sample buffer should be a signed 2's
			 * complement value.
			 */
			if (adc_channels[i].channel_cfg.differential) {
				val_mv = (int32_t)((int16_t)buf);
			} else {
				val_mv = (int32_t)buf;
			}
			printk("%"PRId32, val_mv);
			err = adc_raw_to_millivolts_dt(&adc_channels[i],
						       &val_mv);
			/* conversion to mV may not be supported, skip if not */
			if (err < 0) {
				printk(" (value in mV not available)\n");
			} else {
				printk(" = %"PRId32" mV\n", val_mv);
			}
		}

		k_sleep(K_MSEC(1000));
	}

	uart_suspend();

	// Wait forever
	while (1) {
		k_sleep(K_MSEC(1000));
	}

	return 0;
}

RE: ADC Peripheral Power Management on NRF52840 (BMD-340)

rschimandle — Fri, 21 Feb 2025 15:22:15 GMT

There is no "stop" API call, how do you stop the sample sequence? If there is not a way to explicitly stop the sample sequence can i configure for "single sample" or "single shot" mode?

RE: ADC Peripheral Power Management on NRF52840 (BMD-340)

Einar Thorsrud — Fri, 21 Feb 2025 13:52:23 GMT

Hi,

Do yo make sure to stop ongoin sampling before calling your ADC_Disable() function?