SAM0: Inability to configure ADC for internal temperature sensor

[toshbi4]

Describe the bug

Controller: SamL21 (samr34j18b)

Problem: Following this condition in SAM0 ADC driver (https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/adc/adc_sam0.c#L462) we can initialize ADC driver only with the corresponding controller's pins. However, internal ADC temperature measurement in SUPC isn't provided with any controller's pins. Hence, we can't use this ADC driver for reading ADC values with internal temperature measurements.

Testing: A simple and direct solution - to comment out this condition (pinctrl checking) - made a success, so it means that it is redundant for this particular case...

Expected behavior

It seems that the structure of ADC driver should be made in such a way, that we can optionally check providing of pinctrl structure. For example, we can check for specific channels, where there is no need in any pins for adc.

Impact

Without dealing with this problem I can't implement temperature measurement in a device, what is critical feature for functionality.

Environment (please complete the following information):

• OS: Linux
• Toolchain: Zephyr SDK
• Commit SHA: c69986da4caa0a05b46435b119d58a26d7518138

Additional context

Link to SAM documentation about internal temperature sensor (page 947, "Device Temperature Measurement"): https://ww1.microchip.com/downloads/en/DeviceDoc/SAM_L21_Family_DataSheet_DS60001477C.pdf

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[guenzel-kinexon]

You should be able to achieve what you want with a channel definition and setting the input-positive property to the correct (internal) channel, don't you?

&adc {
// ....
channel@0 {
        reg = <0>;
        zephyr,gain = "ADC_GAIN_1";
        zephyr,reference = "ADC_REF_INTERNAL";
        zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
        zephyr,resolution = <12>;
        zephyr,input-positive = <0x18>;
    };
};

[toshbi4]

You should be able to achieve what you want with a channel definition and setting the input-positive property to the correct (internal) channel, don't you?

&adc {
// ....
channel@0 {
      reg = <0>;
      zephyr,gain = "ADC_GAIN_1";
      zephyr,reference = "ADC_REF_INTERNAL";
      zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
      zephyr,resolution = <12>;
      zephyr,input-positive = <0x18>;
  };
};

Thank you for your answer! This didn't help, unfortunately

But I dealt with this in another way: To avoid triggering this condition you can just create empty pinctrl definition. For example:

pinctrl.dtsi

adc_pins_default: adc_pins_default {
    };

overlay.dts

&adc {
    label = "ADC_TEMP";
    status = "okay";
    pinctrl-0 = <&adc_pins_default>;
    pinctrl-names = "default";
};