NRF54L15 - adc_channel_setup_dt - Invalid argument (-22)

[Leschge]

Based on the DevAcademy here is my following setup using a custom NRF54L15 chip with the NRF54L15-DK devicetree with following overlay:

/ {
    zephyr,user {
        io-channels = <&adc 1>;
    };


    chosen {
        zephyr,console = &uart21;
        zephyr,shell-uart = &uart21;
        zephyr,uart-mcumgr = &uart21;
        zephyr,bt-mon-uart = &uart21;
        zephyr,bt-c2h-uart = &uart21;
    };

    aliases {
        /delete-property/ led3;
        /delete-property/ sw3;
        /delete-property/ sw2;
        /delete-property/ sw1;
        /delete-property/ sw0;
    };
};


/delete-node/ &button0;
/delete-node/ &button1;
/delete-node/ &button2;
/delete-node/ &button3;
/delete-node/ &{/buttons/};
/delete-node/ &led3;

&led0 {
    gpios = <&gpio1 7 0>; // B
    label = "BLUE LED 0";
};

&led1 {
    gpios = <&gpio1 6 0>; // G
    label = "GREEN LED 1";
};

&led2 {
    gpios = <&gpio1 8 0>; // R
    label = "RED LED 2";
};

&adc {
    status = "okay";
    #address-cells = <1>;
    #size-cells = <0>;
    channel@1 {
        reg = <1>;
        zephyr,gain = "ADC_GAIN_1_6";
        zephyr,reference = "ADC_REF_INTERNAL";
        zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 40)>; // Increased to 40us for your 2M Ohm divider
        zephyr,input-positive = <NRF_SAADC_AIN1>;
        zephyr,resolution = <12>;
    };
};

&spi20 {
    status = "okay";
    pinctrl-0 = <&spi20_default>;
    pinctrl-1 = <&spi20_sleep>;
    pinctrl-names = "default", "sleep";
    cs-gpios = <&gpio1 13 0>;
};

&uart20 {
    status = "disabled";
};

&uart21 {
    status = "okay";
    current-speed = <115200>;
    pinctrl-0 = <&uart21_default>;
    pinctrl-1 = <&uart21_sleep>;
    pinctrl-names = "default", "sleep";
};

&pinctrl {
    uart21_default: uart21_default {
        group1 {
            psels = <NRF_PSEL(UART_TX, 1, 4)>;
        };
        group2 {
            psels = <NRF_PSEL(UART_RX, 1, 3)>;
            bias-pull-up;
        };
    };

    uart21_sleep: uart21_sleep {
        group1 {
            psels = 
            <NRF_PSEL(UART_TX, 1, 4)>, 
            <NRF_PSEL(UART_RX, 1, 3)>;
            low-power-enable;
        };
    };

    spi20_default: spi20_default {
        group1 {
            psels = <NRF_PSEL(SPIM_SCK, 1, 11)>,
                    <NRF_PSEL(SPIM_MOSI, 1, 10)>,
                    <NRF_PSEL(SPIM_MISO, 1, 0)>;
        };
    };

    spi20_sleep: spi20_sleep {
        group1 {
            psels = <NRF_PSEL(SPIM_SCK, 1, 11)>;
        };
    };
};

prj.conf:

CONFIG_GPIO=y

CONFIG_ADC=y


code:

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

/* Divider calculation remains in C as it's math-based:
 * (2M + 510k) / 510k = 4.9215...
 */
#define BATTERY_DIVIDER_FACTOR 4.9215f

int16_t sample_buffer;

int read_battery_voltage(void)
{
    int err;

    /* 1. Check if the device is ready */
    if (!adc_is_ready_dt(&adc_channel))
    {
        printk("ADC device not ready\n");
        return -1;
    }

    /* 2. Setup the channel once (from DT) */
    err = adc_channel_setup_dt(&adc_channel);
    if (err < 0)
    {
        printk("Could not setup channel (%d)\n", err);
        return -1;
    }

    /* 3. Prepare the sequence */
    struct adc_sequence sequence = {
        .buffer = &sample_buffer,
        .buffer_size = sizeof(sample_buffer),
        // All other fields (resolution, channels) are pulled from DT by macros below
    };
    adc_sequence_init_dt(&adc_channel, &sequence);

    /* 4. Perform the read */
    err = adc_read_dt(&adc_channel, &sequence);
    if (err < 0)
    {
        printk("ADC read failed (%d)\n", err);
        return -1;
    }

    int32_t mv_value = sample_buffer;

    /* 5. Convert raw value to mV using DT-specific helper */
    err = adc_raw_to_millivolts_dt(&adc_channel, &mv_value);
    if (err < 0)
    {
        return -1;
    }

    /* 6. Scale back up to actual battery voltage */
    return (int)(mv_value * BATTERY_DIVIDER_FACTOR);
}

ADC pin is 1.05. I also tried to use  io-channels = <&adc 0>; with channel@1 and also with ADC_ACQ_TIME_DEFAULT but no luck either.
Always get Could not setup channel (-22)

Appreciate any help.

[Syed Maysum Abbas Zaidi]

Hi,

Thanks for the detailed setup and code. The -22 (EINVAL) is most likely caused by an unsupported ADC gain setting on nRF54L15. Could you please try changing the channel gain in &adc to ADC_GAIN_1_4 in your devicetree:

zephyr,gain = "ADC_GAIN_1_4";

This gain is recommended for nRF54L15 and is used in nRF Connect SDK Intermediate Course. Let us know if this resolves the issue.

Best Regards,
Syed Maysum

[Leschge]

Thanks a lot for the fast support! It worked. I am wondering where its documented that ADC_GAIN_1_6 is not supported? I also skimmed through the sdk code but did not find it.

Edit: Also where do I find which refrerence input can be set? E.g. ADC_REF_VDD_1 also leads to error -22

[Syed Maysum Abbas Zaidi]

Hi,

Could you please share which NCS version you are using? I’d like to double-check the behavior of ADC_GAIN_1_6.

Regarding the reference selection, as mentioned in SAADC reference SAADC driver supports ADC_REF_INTERNAL (which maps to the 0.9 V internal reference) and external reference. For an external reference, it is recommended to stay within +-5% of the internal reference voltage.

Best Regards,
Syed Maysum

[Leschge]

3.0.2

[Syed Maysum Abbas Zaidi]

Hi,

Thanks for your response. You can check the following link showing the supported gains:

https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/saadc.html#ariaid-title52

Which shows that nRF54L15 hardware does not support 1/6 gain.

Best Regards,
Syed Maysum