RE: Setting up multiple ADC channels in the device tree

Ted H — Thu, 21 Jul 2022 13:56:50 GMT

Hi Carl,

Thank you for the reply. In fact, I used the DT macro to enable the GPIO pins but was unsuccessful with the ADC stuff. The only relevant part was:

&adc {
    // compatible = "nordic_nrf_saadc"; // only used to instantiate the NRF_SAADC-peripheral on the chip
    status = "okay";
    // io-channels = <&adc 0>, <&adc 1>, <&adc 2>, <&adc 3>, <&adc 4>, <&adc 5>, <&adc 6>, <&adc 7>;
    // io-channel-names = "VCM2", "READ2_MCU", "READ3_MCU", "VCM3", "VCM1", "READ1_MCU", "VCM4", "READ4_MCU";
};

Please note that it didn't need the io-channels to be specified in the overlay file, but those were configured in the source code side instead and it worked fine:

#define ADC_DEVICE_NAME "ADC_0"
#define ADC_RESOLUTION 10
#define ADC_GAIN ADC_GAIN_1_4
#define ADC_REFERENCE ADC_REF_VDD_1_4
#define ADC_ACQUISITION_TIME ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)

// READ4 Channel
#define AIN6_VCM_CHANNEL_ID 6
#define AIN6_VCM_CHANNEL_INPUT NRF_SAADC_INPUT_AIN6
#define AIN7_READ4_MCU_CHANNEL_ID 7
#define AIN7_READ4_MCU_CHANNEL_INPUT NRF_SAADC_INPUT_AIN7

static const struct adc_channel_cfg m_read4_channel_cfg = {
    .gain = ADC_GAIN,
    .reference = ADC_REFERENCE,
    .acquisition_time = ADC_ACQUISITION_TIME,
    .channel_id = AIN7_READ4_MCU_CHANNEL_ID,
    .differential = 1,
#if defined(CONFIG_ADC_CONFIGURABLE_INPUTS)
    .input_positive = AIN7_READ4_MCU_CHANNEL_INPUT,
    .input_negative = AIN6_VCM_CHANNEL_INPUT,
#endif
};

err = adc_channel_setup(adc_dev, &m_read4_channel_cfg);
if (err) {
    printk("Error in setting up the READ4_MCU: %d\n", err);
}

So my question is, what are the benefits of instantiating these ADC channels in the device tree rather than doing it in the source code?

RE: Setting up multiple ADC channels in the device tree

Carl Richard — Mon, 20 Jun 2022 17:14:55 GMT

Hello, Ted!

Have you had a look at the Device Tree API documentation for IO Channels? Specifically the DT_IO_CHANNELS_INPUT_BY_NAME macro. I haven't tried these myself, but from what I can see they fit your requirements.

Regarding your second question I believe you can instantiate all the channels in a single node like they have done in the example code in the documentation.

Best regards,
Carl Richard