Add support for measuring battery voltage

src/battery.c

@@ -0,0 +1,68 @@
+#include <device.h>
+#include <drivers/adc.h>
+
+#include "battery.h"
+
+#define VBATT DT_PATH(vbatt)
+#define BATTERY_ADC_GAIN ADC_GAIN_1_6
+
+static struct {
+    const struct device *adc;
+    uint32_t output_resistance_ohm;
+    uint32_t full_resistance_ohm;
+    struct adc_sequence sequence;
+    uint16_t raw_value;
+    uint16_t value_mv;
+} battery_adc_config;
+
+int battery_init() {
+    struct adc_channel_cfg config;
+
+    battery_adc_config.adc = device_get_binding(DT_IO_CHANNELS_LABEL(VBATT));
+    if (!battery_adc_config.adc) {
+        return -ENODEV;
+    }
+
+    battery_adc_config.output_resistance_ohm = DT_PROP(VBATT, output_ohms);
+    battery_adc_config.full_resistance_ohm = DT_PROP(VBATT, full_ohms);
+
+    battery_adc_config.sequence.channels = BIT(0);
+    battery_adc_config.sequence.buffer = &battery_adc_config.raw_value;
+    battery_adc_config.sequence.buffer_size = sizeof(battery_adc_config.raw_value);
+    battery_adc_config.sequence.oversampling = 4;
+    battery_adc_config.sequence.calibrate = true;
+    battery_adc_config.sequence.resolution = 14;
+
+    config.gain = BATTERY_ADC_GAIN;
+    config.reference = ADC_REF_INTERNAL;
+    config.acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 40);
+    config.channel_id = 0;
+    config.input_positive = SAADC_CH_PSELP_PSELP_AnalogInput0 + DT_IO_CHANNELS_INPUT(VBATT);
+
+    return adc_channel_setup(battery_adc_config.adc, &config);
+}
+
+int battery_update() {
+    int err;
+    int32_t val_mv;
+
+    err = adc_read(battery_adc_config.adc, &battery_adc_config.sequence);
+    if (err) {
+        return err;
+    }
+
+    battery_adc_config.sequence.calibrate = false;
+
+    val_mv = battery_adc_config.raw_value;
+    err = dc_raw_to_millivolts(adc_ref_internal(battery_adc_config.adc), BATTERY_ADC_GAIN, battery_adc_config.sequence.resolution, &val_mv);
+    if (err) {
+        return err;
+    }
+
+    battery_adc_config.value_mv = val_mv * battery_adc_config.full_resistance_ohm / battery_adc_config.output_resistance_ohm;
+    return 0;
+}
+
+uint16_t battery_get_voltage_mv() {
+    return battery_adc_config.value_mv;
+}

src/battery.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stdint.h>
+
+int battery_init();
+int battery_update();
+uint16_t battery_get_voltage_mv();

src/display.h

@@ -4,7 +4,8 @@
 #include <stdbool.h>
 
 #define DISPLAY_LINE_CURRENT_IDENTIFIER  0
-#define DISPLAY_LINE_LAST_CONTACTS_START 2
+#define DISPLAY_LINE_LAST_CONTACTS_START 5
+#define DISPLAY_LINE_BATTERY_VOLTAGE     20
 
 #ifdef PLATFORM_PINETIME
 #include "display_pinetime.h"

src/main.c

@@ -11,6 +11,7 @@
 #include <bluetooth/hci.h>
 #include <random/rand32.h>
 
+#include "battery.h"
 #include "exposure-notification.h"
 #include "covid_types.h"
 #include "contacts.h"
@@ -35,6 +36,20 @@ void main(void)
 	platform_display_draw_string(0, 0, "Hello World!");
 	platform_display_draw_string(0, DISPLAY_LINE_LAST_CONTACTS_START, "Seen identifiers:");
 
+	err = battery_init();
+	if (err) {
+		printk("Failed to initialize battery gauging: %d\n", err);
+		return;
+	}
+
+	err = battery_update();
+	if (err) {
+		printk("Failed to update battery voltage: %d\n", err);
+		return;
+	}
+
+	platform_display_draw_string(0, DISPLAY_LINE_BATTERY_VOLTAGE, "Battery voltage:");
+
     // first init everything
 	// Use custom randomization as the mbdet_tls context initialization messes with the Zeyhr BLE stack.
     err = en_init(sys_csrand_get);
@@ -72,7 +87,16 @@ void main(void)
 		return;
 	}
 
-	do{
+	do {
+		err = battery_update();
+		if (err) {
+			printk("Failed to update battery voltage: %d\n", err);
+		} else {
+			char voltage_mv[12] = { 0 };
+
+			snprintf(voltage_mv, sizeof(voltage_mv), "%04u mV", battery_get_voltage_mv());
+			platform_display_draw_string(0, DISPLAY_LINE_BATTERY_VOLTAGE + 1, voltage_mv);
+		}
 		do_covid();
 		do_gatt();
 	} while (1);

zephyr/pinetime_devkit0.overlay

@@ -0,0 +1,12 @@
+&adc {
+    status = "okay";
+};
+
+/ {
+    vbatt {
+        compatible = "voltage-divider";
+        io-channels = <&adc 7>;
+        output-ohms = <1000000>;
+        full-ohms = <(1000000 + 1000000)>;
+    };
+};

zephyr/prj.conf

@@ -24,6 +24,7 @@ CONFIG_HEAP_MEM_POOL_SIZE=8192
 
 CONFIG_GPIO=y
 CONFIG_LED=y
+CONFIG_ADC=y
 
 #CONFIG_LVGL=y
 #CONFIG_LVGL_USE_LABEL=y