OS: Windows 11 Pro
OS Version: 10.0.22631
Toolchain: nRF Connect SDK (VS Code Extension) version 2.9.0
Hardware: BMD-340
Our Implementation requires disabling the ADC peripheral while not in use to conserve power.
Issue: While attempting to disable the peripheral through the function call void ADC_Disable(void) or enable the peripheral through the function call void ADC_Enable(void), the peripheral is not able to change it's power state. The error output shows the following:
[00:00:59.810,058] <err> battery_monitor: Failed to resume ADC: -88
[00:01:05.235,168] <err> battery_monitor: Failed to suspend ADC: -88
Looking up the error shows the following:
ENOSYS 88
Function not implemented.
Question: What configuration or code needs to be added to be able to manage the ADC peripheral power?
The current device tree configuration is provided below:
&adc {
status = "okay";
#address-cells = <1>;
#size-cells = <0>;
zephyr,pm-device-runtime-auto;
channel@0 {
reg = <0>;
zephyr,gain = "ADC_GAIN_1_6";
zephyr,reference = "ADC_REF_INTERNAL";
zephyr,resolution = <12>;
zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 20)>;
zephyr,input-positive = <NRF_SAADC_VDD>;
};
};
We have written a function for monitoring the battery voltage of the device which enables the peripheral, takes a sample, then disables the peripheral. I have provided the Implementation Below:
AdcBattery.h
#ifndef ADC_BATTERY_H
#define ADC_BATTERY_H
#include <stdint.h>
#include <zephyr/device.h>
#include <zephyr/drivers/adc.h>
#include "SystemConfig.h"
#ifdef DEBUG_BATTERY_MONITORING
#define BATTERY_VOLTAGE_READ_PERIOD_SECONDS 10
#else
#define BATTERY_VOLTAGE_READ_PERIOD_SECONDS 43200 /** Period in which the battery voltage will be read in seconds. 43200 = 12 hours (twice per day) */
#endif
/**
* @brief Initializes the ADC peripheral for battery voltage measurement.
*/
void ADC_Init(void);
/**
* @brief Disables the ADC peripheral to conserve power.
*/
void ADC_Disable(void);
/**
* @brief Enables the ADC peripheral to obtain a sample.
*/
void ADC_Enable(void);
/**
* @brief Reads the battery voltage and returns it as millivolts (mV * 1000).
*
* @return uint16_t The battery voltage in millivolts x 1000.
*/
uint16_t ADC_GetBatteryVoltage(void);
#endif // ADC_BATTERY_H
AdcBattery.c
#include "AdcBattery.h"
#include <zephyr/kernel.h>
#include <zephyr/sys/printk.h>
#include <zephyr/device.h>
#include <zephyr/drivers/adc.h>
#include <zephyr/devicetree.h>
#include <zephyr/pm/device.h>
#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(battery_monitor, LOG_LEVEL_INF);
#define ADC_RESOLUTION 12
#define ADC_CHANNEL_ID 0
#define ADC_GAIN ADC_GAIN_1_6
#define ADC_REFERENCE_VOLTAGE 600 // Internal reference voltage in millivolts
#define ADC_MAX_COUNTS 4096 // 2^12 for 12-bit resolution
// Use adc_dt_spec for defining ADC channel
static const struct adc_dt_spec adc_channel = ADC_DT_SPEC_GET_BY_NAME(DT_PATH(zephyr_user), a0);
static int16_t adc_sample_buffer;
static bool adc_initialized = false;
static bool adc_enabled = false;
static struct adc_sequence sequence = {
.buffer = &adc_sample_buffer,
.buffer_size = sizeof(int16_t),
};
void ADC_Init(void) {
int err = 0;
if (!adc_is_ready_dt(&adc_channel)) {
LOG_ERR("ADC controller device %s not ready\n", "Battery");
return;
}
err = adc_channel_setup_dt(&adc_channel);
if (err < 0) {
LOG_ERR("Could not setup channel #%d (%d)\n", 0, err);
return;
}
adc_initialized = true;
LOG_INF("ADC initialized using Zephyr DT\n");
}
void ADC_Disable(void) {
enum pm_device_state state;
if (adc_enabled) {
pm_device_state_get(adc_channel.dev, &state);
__NOP();
int ret = pm_device_action_run(adc_channel.dev, PM_DEVICE_ACTION_SUSPEND);
if (ret == 0) {
LOG_INF("ADC suspended\n");
} else {
LOG_ERR("Failed to suspend ADC: %d\n", ret);
}
adc_enabled = false;
}
}
void ADC_Enable(void) {
enum pm_device_state state;
if (!adc_initialized) {
ADC_Init();
} else {
pm_device_state_get(adc_channel.dev, &state);
__NOP();
int ret = pm_device_action_run(adc_channel.dev, PM_DEVICE_ACTION_RESUME);
if (ret == 0) {
LOG_INF("ADC resumed\n");
} else {
LOG_ERR("Failed to resume ADC: %d\n", ret);
}
adc_enabled = true;
}
}
uint16_t ADC_GetBatteryVoltage(void) {
int err = 0;
if ((!adc_initialized) || (!adc_enabled)) {
ADC_Enable();
}
(void)adc_sequence_init_dt(&adc_channel, &sequence);
err = adc_read_dt(&adc_channel, &sequence);
ADC_Disable();
if (err < 0) {
LOG_ERR("Could not read (%d)\n", err);
}
// Convert ADC counts to millivolts: Voltage = (counts / max_counts) * (reference_voltage / gain)
uint16_t voltage_mv = ((uint32_t)adc_sample_buffer * ADC_REFERENCE_VOLTAGE * 6) / ADC_MAX_COUNTS;
return voltage_mv;
}
