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Zephyr ADC Configuration

[TOC]

Overview

ADC is used to measure VBUS, temperature and other values depending on a board.

Kconfig Options

The CONFIG_ADC option enables ADC support in the Zephyr EC application. Use the CONFIG_ADC_SHELL option to enable ADC related shell commands.

Refer to Kconfig.adc for all sub-options related to ADC support that are specific to the Zephyr EC application.

Devicetree Nodes

The EC chip disables all Analog-to-Digital Converters by default. Enable ADC used on your design by changing the chip-specific ADC status property to "okay".

ADC properties:

Property Description Settings
status Enables or disables the ADC module "okay"
"disabled"
label Override the EC chip specific label. "ADC_<number>"

Either Nuvoton NPCX and ITE IT8xxx2 ECs use single a devicetree node adc0 to describe ADC, but it supports multiple ADC channels.

To enable the ADC set the status property to "okay":

&adc0 {
	status = "okay";
};

Mapping legacy ADC enums to ADC channels

The legacy ADC API for the Chromium EC application uses an enumeration (e.g. ADC_VBUS, ADC_AMON_BMON) to specify the ADC channel to measure voltage.

The named-adc-channels node creates the mapping between the legacy ADC channels enumeration and the Zephyr ADC driver's channel_id.

named-adc-channels {
	compatible = "named-adc-channels";
	vbus {
		enum-name = "ADC_VBUS";
		io-channels = <&adc0 1>;
		/* Measure VBUS through a 1/10 voltage divider */
		mul = <10>;
	};
};

Refer to the named-adc.yaml child-binding file for details about each property.

Board Specific Code

None required.

Threads

ADC support does not enable any threads.

Testing and Debugging

Unfortunately, the are two adc console commands: a Zephyr command and the one implemented in CrosEC. Only one of them can be enabled with CONFIG_ADC_SHELL or CONFIG_PLATFORM_EC_ADC_CMD respectively.

Zephyr command {#zephyr-cc}

The Zephyr adc includes the following subcommands:

Subcommand Description Usage
acq_time Configure acquisition time adc <adc_label> acq_time <time> <unit>
channel Configure ADC channel adc <adc_label> channel id <channel_id>
gain Configure gain adc <adc_label> gain <gain>
print Print current configuration adc <adc_label> print
read Read adc value adc <adc_label> read <channel>
reference Configure reference adc <adc_label> reference <reference>
resolution Configure resolution for the read subcommand adc <adc_label> resolution <resolution>

Parameters summary:

Parameter Description
<adc_label> The ADC label property. By default, this is specified by the EC vendor in the respective devicetree include file unless you override the label in your devicetree.
<time> For the acq_time subcommand, specifies the time of acquisition.
<unit> For the acq_time subcommand, specifies the unit of the time of acquisition: us, ns, ticks.
<channel_id> For the channel subcommand, specifies the channel ID.
<gain> For the gain subcommand, specifies the gain of the ADC measurement, e.g. GAIN_1_6, GAIN_2, GAIN_64.
<channel> ADC channel.
<reference> For the reference subcommand, specifies the reference for the ADC measurement, e.g. VDD_1, INTERNAL.
<resolution> For the resolution subcommand, specifies the resolution for the ADC conversion for the read subcommand.

E.g.

21-12-22 13:51:11.380 uart:~$ adc ADC_0 read 5
adc ADC_0 read 5
21-12-22 13:51:26.031 read: 1023

CrosEC command {#crosec-cc}

The CrosEC shell command adc displays current ADC measurements, e.g.

21-12-21 09:58:03.746 uart:~$ adc
adc
21-12-21 09:58:05.322   ADC_VBUS = 14850 mV
21-12-21 09:58:05.325   ADC_AMON_BMON = 37111 mV
21-12-21 09:58:05.325   ADC_PSYS = 8432000 mV

Example

The image below shows the ADC wiring for the Volteer reference board.

ADC Example

The Volteer board uses Nuvoton NPCX EC that has one Analog-to-Digital Converter adc0, so enable it:

&adc0 {
	status = "okay";
};

The board has four temperature sensors handled with ADC. Map legacy cros-ec enums to ADC channels with the following values:

ADC Enumeration Name Volteer ADC channel
ADC_TEMP_SENSOR_CHARGER ADC0
ADC_TEMP_SENSOR_PP3300_REGULATOR ADC1
ADC_TEMP_SENSOR_DDR_SOC ADC8
ADC_TEMP_SENSOR_FAN ADC3

The Volteer project establishes this map using the named-adc-channels as shown below:

named-adc-channels {
	compatible = "named-adc-channels";

	adc_charger: charger {
		enum-name = "ADC_TEMP_SENSOR_CHARGER";
		io-channels = <&adc0 0>;
	};
	adc_pp3300_regulator: pp3300_regulator {
		enum-name = "ADC_TEMP_SENSOR_PP3300_REGULATOR";
		io-channels = <&adc0 1>;
	};
	adc_ddr_soc: ddr_soc {
		enum-name = "ADC_TEMP_SENSOR_DDR_SOC";
		io-channels = <&adc0 8>;
	};
	adc_fan: fan {
		enum-name = "ADC_TEMP_SENSOR_FAN";
		io-channels = <&adc0 3>;
	};
};