ADC Channle Not Configured... adc_nrfx_saadc: Channel 2 not configured

Question

I am programming a RAK4631 Board, which is of course based on the nrf52840 SoC. The BaseLine Device tree has no detail in the ADC Node so I have created an overlay. The RAK4631 documentation indicates that AIN2 (P0.04) is directly connected to the battery for voltage measurement. There are many Arduino examples out there but not many C code examples. Here is my overlay file contents:

/ {

zephyr,user {

io-channels = <&adc 2>, <&adc 7>;

};

&adc {

status = "okay";

#address-cells = <1>;

#size-cells = <0>;

channel@2 {

reg = <2>;

zephyr,gain = "ADC_GAIN_1_6";

zephyr,reference = "ADC_REF_INTERNAL";

zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;

zephyr,input-positive = <NRF_SAADC_AIN2>; /* Corresponds to P0.04 */

zephyr,resolution = <12>;

};

channel@7 {

reg = <7>;

zephyr,gain = "ADC_GAIN_1_6";

zephyr,reference = "ADC_REF_INTERNAL";

zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;

zephyr,input-positive = <NRF_SAADC_AIN7>; /* Corresponds to P0.31 */

zephyr,resolution = <12>;

};

Here is my setup code:

//

// ADC Defines

//

#define BATT_ADC_NODE DT_NODELABEL(adc) // ADC peripheral node

#define ADC_RESOLUTION 12 // 12-bit ADC resolution

#define ADC_GAIN ADC_GAIN_1_6 // Gain setting for ADC

#define ADC_REFERENCE ADC_REF_INTERNAL // Internal reference voltage

#define ADC_ACQUISITION_TIME ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10) // Acquisition time

#define BATTERY_CHANNEL_ID 2 // ADC channel ID for the battery AIN2

#define ADC_MAX_VOLTAGE 3.6 // Maximum ADC input voltage (V)

#define ADC_FULL_SCALE (1 << ADC_RESOLUTION) // Full-scale value for 12-bit ADC

#define VOLTAGE_DIVIDER_RATIO 2.0f

const struct device *batt_adc_dev = DEVICE_DT_GET(BATT_ADC_NODE);

// Define ADC channel configuration

static const struct adc_channel_cfg battery_channel_cfg = {

.gain = ADC_GAIN_1_6,

.reference = ADC_REF_INTERNAL,

.acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10),

.channel_id = BATTERY_CHANNEL_ID, // Specify the channel ID for AIN2

.differential = 0 // Single-ended input

};

// Define ADC sequence

static struct adc_sequence battery_adc_seq = {

.channels = BIT(BATTERY_CHANNEL_ID),

.buffer = NULL, // Buffer will be set dynamically

.buffer_size = 0,

.resolution = ADC_RESOLUTION,

};

I am calling this for setup:

//

// Check AIN Ready for Battery Voltage Read

//

if (!device_is_ready(batt_adc_dev))

{

LOG_ERR("AIN2 Device not ready");

return;

}

else

{

LOG_ERR("AIN2 Device Ready!!");

}

ret = adc_channel_setup(batt_adc_dev, &battery_channel_cfg);

if (ret != 0) {

LOG_ERR("Failed to configure ADC channel: %d", ret);

}else

{

LOG_INF("ADC channel configured for battery voltage measurement");

}

These calls are all successful.

However, when I call this:

int ret = adc_read(batt_adc_dev, &battery_adc_seq);

if (ret < 0) {

LOG_ERR("Failed to read ADC: %d", ret);

return -1.0f;

}

I always get this log message:

00> [00:30:35.901,824] <err> adc_nrfx_saadc: Channel 2 not configured
00> [00:30:36.002,075] <err> ublox_gps: Failed to read ADC: -22

The project builds successfully without warnings or errors. Any help letting me know where I am going wrong would be appreciated. I am using Zephyr v2.9.0 which I believe is the latest and the RAK4631 dev board.

Thank you.

eq · Answer

This Ticket can be closed. I found an example that used zypher_user to access the overlay nodes, which was the trick!

eq · Answer

Hi Martin, a couple of things. In my initial setup, I used the zephyr user to get the device context like this:

static const struct adc_dt_spec adc_channel = ADC_DT_SPEC_GET(DT_PATH(zephyr_user));

int16_t buf;
struct adc_sequence sequence = {
.buffer = &buf,
/* buffer size in bytes, not number of samples */
.buffer_size = sizeof(buf),
// Optional
//.calibrate = true,
};

My initialization was then this:

//
// Initialize ADC for Battery Voltage Measurement
//
/* STEP 3.3 - validate that the ADC peripheral (SAADC) is ready */
if (!adc_is_ready_dt(&adc_channel)) {
LOG_ERR("ADC controller device %s not ready", adc_channel.dev->name);
return;
}
/* STEP 3.4 - Setup the ADC channel */
int err = adc_channel_setup_dt(&adc_channel);
if (err < 0) {
LOG_ERR("Could not setup channel #%d (%d)", 0, err);
return;
}
/* STEP 4.2 - Initialize the ADC sequence */
err = adc_sequence_init_dt(&adc_channel, &sequence);
if (err < 0) {
LOG_ERR("Could not initalize sequnce");
return;
}

And then measuring:

LOG_INF("Reading Battery Voltage...");

int val_mv;
uint32_t count = 0;

/* STEP 5 - Read a sample from the ADC */
int err = adc_read(adc_channel.dev, &sequence);
if (err < 0) {
LOG_ERR("Could not read (%d)", err);
return 0.0;
}

val_mv = (int)buf;
LOG_INF("ADC reading[%u]: %s, channel %d: Raw: %d", count++, adc_channel.dev->name, adc_channel.channel_id, val_mv);

/* STEP 6 - Convert raw value to mV*/
err = adc_raw_to_millivolts_dt(&adc_channel, &val_mv);
/* conversion to mV may not be supported, skip if not */
if (err < 0) {
LOG_WRN(" (value in mV not available)\n");
} else {
LOG_INF("Unscaled voltage = %d mV", val_mv);
}
/* Calculate the battery voltage */
float battery_voltage = (val_mv / 1000.0) / VOLTAGE_DIVIDER_RATIO;

Oh yeah, how can i forget. The big confusion point was this in my overlay file:

zephyr,input-positive = <NRF_SAADC_AIN3>; /* Corresponds to P0.04 */

I had mistakenly been using AIN4!!!

I hope this helps!

EQ