add example using the usb_c vbus driver

Signed-off-by: Mark Kettner <mark@kettner.io>

samples/drivers/vbatt/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(vbatt)
+
+target_sources(app PRIVATE src/main.c)

samples/drivers/vbatt/README.rst

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+.. _vbatt_sample:
+
+Battery Voltage Measurement Sample
+##################################
+
+Overview
+********
+
+This sample demonstrates how one can use the configuration of the Zephyr ADC infrastructure to
+measure the voltage of the device power supply using a voltage-divider. The sample assumes a
+regulator that provides a fixed voltage to IO38 of the esp32 behind a voltage divider. In this
+sample the voltage divider consists of 300k and 100k Ohms resistors. It will then print the measured
+battery voltage to the console. If you take care to not power the device thru the usb port, you can
+see how the battery voltage decreases over time, Thus indicating the current charging level.
+
+Application Details
+===================
+
+The application initializes battery measurement on startup, then loops
+displaying the battery status every five seconds.
+
+Requirements
+************
+
+A charging regulator (e.g. MAX777) connected to a voltage divider to the
+
+
+Building and Running
+********************
+
+This application can be built and executed on QEMU as follows:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/drivers/vbatt
+   :host-os: unix
+   :board: esp32_devkitc_wrover
+   :goals: build flash
+   :compact:
+
+To build for another board, change "qemu_x86" above to that board's name.
+
+Sample Output
+=============
+
+.. code-block:: console
+
+    bat=1.85V
+    bat=1.80V
+    bat=1.85V
+    bat=1.80V

samples/drivers/vbatt/boards/esp32_devkitc_wrover.overlay

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+/ {
+	aliases {
+		battery = &vbatt;
+	};
+
+	vbatt: vbatt {
+		compatible = "zephyr,usb-c-vbus-adc";
+		status = "okay";
+		io-channels = <&adc0 3>;
+		output-ohms = <300000>;
+		full-ohms = <(300000 + 100000)>;
+	};
+
+};
+
+&adc0 {
+	status = "okay";
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	channel@3 {
+		reg = <3>;
+		zephyr,gain = "ADC_GAIN_1_4";
+		zephyr,reference = "ADC_REF_INTERNAL";
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,resolution = <12>;
+	};
+};

samples/drivers/vbatt/prj.conf

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+CONFIG_USBC_VBUS_ADC=y
+CONFIG_USBC_VBUS_DRIVER=y
+
+CONFIG_GPIO=y
+CONFIG_ADC=y

samples/drivers/vbatt/src/main.c

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+#include <zephyr/device.h>
+#include <zephyr/drivers/usb_c/usbc_vbus.h>
+
+#include <zephyr/kernel.h>
+#define BAT_NODE DT_ALIAS(battery)
+static const struct device *bat_dev = DEVICE_DT_GET(BAT_NODE);
+
+int main(void)
+{
+	int rc = 0;
+	int mea;
+	for(;;) {
+          usbc_vbus_measure(bat_dev, &mea);
+	  printf("bat=%i.%iV", mea/100,mea%100);
+	  k_sleep(K_SECONDS(5));
+        }
+}