refactor: Move drivers into properly module.

* Align our driver module layout to properly match Zephyr conventions,
  allowing proper CMake setup to amend the library for each type of driver.

app/module/drivers/sensor/battery/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Copyright (c) 2020-2021 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+zephyr_include_directories(.)
+
+zephyr_library()
+
+zephyr_library_sources(battery_common.c)
+zephyr_library_sources_ifdef(CONFIG_ZMK_BATTERY_NRF_VDDH battery_nrf_vddh.c)
+zephyr_library_sources_ifdef(CONFIG_ZMK_BATTERY_VOLTAGE_DIVIDER battery_voltage_divider.c)

app/module/drivers/sensor/battery/Kconfig

@@ -0,0 +1,28 @@
+# Copyright (c) 2020-2021 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+
+DT_COMPAT_ZMK_BATTERY_NRF_VDDH := zmk,battery-nrf-vddh
+DT_COMPAT_ZMK_BATTERY_VOLTAGE_DIVIDER := zmk,battery-voltage-divider
+
+config ZMK_BATTERY
+    bool "ZMK battery monitoring"
+    help
+        Enable battery monitoring
+
+config ZMK_BATTERY_NRF_VDDH
+    bool
+    default $(dt_compat_enabled,$(DT_COMPAT_ZMK_BATTERY_NRF_VDDH))
+    select ADC
+    select ZMK_BATTERY
+    depends on SENSOR
+    help
+        Enable ZMK nRF VDDH voltage driver for battery monitoring.
+
+config ZMK_BATTERY_VOLTAGE_DIVIDER
+    bool
+    default $(dt_compat_enabled,$(DT_COMPAT_ZMK_BATTERY_VOLTAGE_DIVIDER))
+    select ADC
+    select ZMK_BATTERY
+    depends on SENSOR
+    help
+        Enable ZMK battery voltage divider driver for battery monitoring.

app/module/drivers/sensor/battery/battery_common.c

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2021 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <errno.h>
+#include <zephyr/drivers/sensor.h>
+
+#include "battery_common.h"
+
+int battery_channel_get(const struct battery_value *value, enum sensor_channel chan,
+                        struct sensor_value *val_out) {
+    switch (chan) {
+    case SENSOR_CHAN_GAUGE_VOLTAGE:
+        val_out->val1 = value->millivolts / 1000;
+        val_out->val2 = (value->millivolts % 1000) * 1000U;
+        break;
+
+    case SENSOR_CHAN_GAUGE_STATE_OF_CHARGE:
+        val_out->val1 = value->state_of_charge;
+        val_out->val2 = 0;
+        break;
+
+    default:
+        return -ENOTSUP;
+    }
+
+    return 0;
+}
+
+uint8_t lithium_ion_mv_to_pct(int16_t bat_mv) {
+    // Simple linear approximation of a battery based off adafruit's discharge graph:
+    // https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages
+
+    if (bat_mv >= 4200) {
+        return 100;
+    } else if (bat_mv <= 3450) {
+        return 0;
+    }
+
+    return bat_mv * 2 / 15 - 459;
+}

app/module/drivers/sensor/battery/battery_common.h

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2021 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#pragma once
+
+#include <zephyr/drivers/sensor.h>
+#include <stdint.h>
+
+struct battery_value {
+    uint16_t adc_raw;
+    uint16_t millivolts;
+    uint8_t state_of_charge;
+};
+
+int battery_channel_get(const struct battery_value *value, enum sensor_channel chan,
+                        struct sensor_value *val_out);
+
+uint8_t lithium_ion_mv_to_pct(int16_t bat_mv);

app/module/drivers/sensor/battery/battery_nrf_vddh.c

@@ -0,0 +1,116 @@
+/*
+ * Copyright (c) 2021 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * This is a simplified version of battery_voltage_divider.c which always reads
+ * the VDDHDIV5 channel of the &adc node and multiplies it by 5.
+ */
+
+#define DT_DRV_COMPAT zmk_battery_nrf_vddh
+
+#include <zephyr/device.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/drivers/adc.h>
+#include <zephyr/drivers/sensor.h>
+#include <zephyr/logging/log.h>
+
+#include "battery_common.h"
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+#define VDDHDIV (5)
+
+static const struct device *adc = DEVICE_DT_GET(DT_NODELABEL(adc));
+
+struct vddh_data {
+    struct adc_channel_cfg acc;
+    struct adc_sequence as;
+    struct battery_value value;
+};
+
+static int vddh_sample_fetch(const struct device *dev, enum sensor_channel chan) {
+    // Make sure selected channel is supported
+    if (chan != SENSOR_CHAN_GAUGE_VOLTAGE && chan != SENSOR_CHAN_GAUGE_STATE_OF_CHARGE &&
+        chan != SENSOR_CHAN_ALL) {
+        LOG_DBG("Selected channel is not supported: %d.", chan);
+        return -ENOTSUP;
+    }
+
+    struct vddh_data *drv_data = dev->data;
+    struct adc_sequence *as = &drv_data->as;
+
+    int rc = adc_read(adc, as);
+    as->calibrate = false;
+
+    if (rc != 0) {
+        LOG_ERR("Failed to read ADC: %d", rc);
+        return rc;
+    }
+
+    int32_t val = drv_data->value.adc_raw;
+    rc = adc_raw_to_millivolts(adc_ref_internal(adc), drv_data->acc.gain, as->resolution, &val);
+    if (rc != 0) {
+        LOG_ERR("Failed to convert raw ADC to mV: %d", rc);
+        return rc;
+    }
+
+    drv_data->value.millivolts = val * VDDHDIV;
+    drv_data->value.state_of_charge = lithium_ion_mv_to_pct(drv_data->value.millivolts);
+
+    LOG_DBG("ADC raw %d ~ %d mV => %d%%", drv_data->value.adc_raw, drv_data->value.millivolts,
+            drv_data->value.state_of_charge);
+
+    return rc;
+}
+
+static int vddh_channel_get(const struct device *dev, enum sensor_channel chan,
+                            struct sensor_value *val) {
+    struct vddh_data const *drv_data = dev->data;
+    return battery_channel_get(&drv_data->value, chan, val);
+}
+
+static const struct sensor_driver_api vddh_api = {
+    .sample_fetch = vddh_sample_fetch,
+    .channel_get = vddh_channel_get,
+};
+
+static int vddh_init(const struct device *dev) {
+    struct vddh_data *drv_data = dev->data;
+
+    if (!device_is_ready(adc)) {
+        LOG_ERR("ADC device is not ready %s", adc->name);
+        return -ENODEV;
+    }
+
+    drv_data->as = (struct adc_sequence){
+        .channels = BIT(0),
+        .buffer = &drv_data->value.adc_raw,
+        .buffer_size = sizeof(drv_data->value.adc_raw),
+        .oversampling = 4,
+        .calibrate = true,
+    };
+
+#ifdef CONFIG_ADC_NRFX_SAADC
+    drv_data->acc = (struct adc_channel_cfg){
+        .gain = ADC_GAIN_1_2,
+        .reference = ADC_REF_INTERNAL,
+        .acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 40),
+        .input_positive = SAADC_CH_PSELN_PSELN_VDDHDIV5,
+    };
+
+    drv_data->as.resolution = 12;
+#else
+#error Unsupported ADC
+#endif
+
+    const int rc = adc_channel_setup(adc, &drv_data->acc);
+    LOG_DBG("VDDHDIV5 setup returned %d", rc);
+
+    return rc;
+}
+
+static struct vddh_data vddh_data;
+
+DEVICE_DT_INST_DEFINE(0, &vddh_init, NULL, &vddh_data, NULL, POST_KERNEL,
+                      CONFIG_SENSOR_INIT_PRIORITY, &vddh_api);

app/module/drivers/sensor/battery/battery_voltage_divider.c

@@ -0,0 +1,175 @@
+/*
+ * Copyright (c) 2020 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#define DT_DRV_COMPAT zmk_battery_voltage_divider
+
+#include <zephyr/device.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/drivers/gpio.h>
+#include <zephyr/drivers/adc.h>
+#include <zephyr/drivers/sensor.h>
+#include <zephyr/logging/log.h>
+
+#include "battery_common.h"
+
+LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
+
+struct io_channel_config {
+    uint8_t channel;
+};
+
+struct bvd_config {
+    struct io_channel_config io_channel;
+    struct gpio_dt_spec power;
+    uint32_t output_ohm;
+    uint32_t full_ohm;
+};
+
+struct bvd_data {
+    const struct device *adc;
+    struct adc_channel_cfg acc;
+    struct adc_sequence as;
+    struct battery_value value;
+};
+
+static int bvd_sample_fetch(const struct device *dev, enum sensor_channel chan) {
+    struct bvd_data *drv_data = dev->data;
+    const struct bvd_config *drv_cfg = dev->config;
+    struct adc_sequence *as = &drv_data->as;
+
+    // Make sure selected channel is supported
+    if (chan != SENSOR_CHAN_GAUGE_VOLTAGE && chan != SENSOR_CHAN_GAUGE_STATE_OF_CHARGE &&
+        chan != SENSOR_CHAN_ALL) {
+        LOG_DBG("Selected channel is not supported: %d.", chan);
+        return -ENOTSUP;
+    }
+
+    int rc = 0;
+
+#if DT_INST_NODE_HAS_PROP(0, power_gpios)
+    // Enable power before sampling
+    rc = gpio_pin_set_dt(&drv_cfg->power, 1);
+
+    if (rc != 0) {
+        LOG_DBG("Failed to enable ADC power GPIO: %d", rc);
+        return rc;
+    }
+
+    // wait for any capacitance to charge up
+    k_sleep(K_MSEC(10));
+#endif // DT_INST_NODE_HAS_PROP(0, power_gpios)
+
+    // Read ADC
+    rc = adc_read(drv_data->adc, as);
+    as->calibrate = false;
+
+    if (rc == 0) {
+        int32_t val = drv_data->value.adc_raw;
+
+        adc_raw_to_millivolts(adc_ref_internal(drv_data->adc), drv_data->acc.gain, as->resolution,
+                              &val);
+
+        uint16_t millivolts = val * (uint64_t)drv_cfg->full_ohm / drv_cfg->output_ohm;
+        LOG_DBG("ADC raw %d ~ %d mV => %d mV", drv_data->value.adc_raw, val, millivolts);
+        uint8_t percent = lithium_ion_mv_to_pct(millivolts);
+        LOG_DBG("Percent: %d", percent);
+
+        drv_data->value.millivolts = millivolts;
+        drv_data->value.state_of_charge = percent;
+    } else {
+        LOG_DBG("Failed to read ADC: %d", rc);
+    }
+
+#if DT_INST_NODE_HAS_PROP(0, power_gpios)
+    // Disable power GPIO if present
+    int rc2 = gpio_pin_set_dt(&drv_cfg->power, 0);
+
+    if (rc2 != 0) {
+        LOG_DBG("Failed to disable ADC power GPIO: %d", rc2);
+        return rc2;
+    }
+#endif // DT_INST_NODE_HAS_PROP(0, power_gpios)
+
+    return rc;
+}
+
+static int bvd_channel_get(const struct device *dev, enum sensor_channel chan,
+                           struct sensor_value *val) {
+    struct bvd_data *drv_data = dev->data;
+    return battery_channel_get(&drv_data->value, chan, val);
+}
+
+static const struct sensor_driver_api bvd_api = {
+    .sample_fetch = bvd_sample_fetch,
+    .channel_get = bvd_channel_get,
+};
+
+static int bvd_init(const struct device *dev) {
+    struct bvd_data *drv_data = dev->data;
+    const struct bvd_config *drv_cfg = dev->config;
+
+    if (drv_data->adc == NULL) {
+        LOG_ERR("ADC failed to retrieve ADC driver");
+        return -ENODEV;
+    }
+
+    int rc = 0;
+
+#if DT_INST_NODE_HAS_PROP(0, power_gpios)
+    if (!device_is_ready(drv_cfg->power.port)) {
+        LOG_ERR("GPIO port for power control is not ready");
+        return -ENODEV;
+    }
+    rc = gpio_pin_configure_dt(&drv_cfg->power, GPIO_OUTPUT_INACTIVE);
+    if (rc != 0) {
+        LOG_ERR("Failed to control feed %u: %d", drv_cfg->power.pin, rc);
+        return rc;
+    }
+#endif // DT_INST_NODE_HAS_PROP(0, power_gpios)
+
+    drv_data->as = (struct adc_sequence){
+        .channels = BIT(0),
+        .buffer = &drv_data->value.adc_raw,
+        .buffer_size = sizeof(drv_data->value.adc_raw),
+        .oversampling = 4,
+        .calibrate = true,
+    };
+
+#ifdef CONFIG_ADC_NRFX_SAADC
+    drv_data->acc = (struct adc_channel_cfg){
+        .gain = ADC_GAIN_1_6,
+        .reference = ADC_REF_INTERNAL,
+        .acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 40),
+        .input_positive = SAADC_CH_PSELP_PSELP_AnalogInput0 + drv_cfg->io_channel.channel,
+    };
+
+    drv_data->as.resolution = 12;
+#else
+#error Unsupported ADC
+#endif
+
+    rc = adc_channel_setup(drv_data->adc, &drv_data->acc);
+    LOG_DBG("AIN%u setup returned %d", drv_cfg->io_channel.channel, rc);
+
+    return rc;
+}
+
+static struct bvd_data bvd_data = {.adc = DEVICE_DT_GET(DT_IO_CHANNELS_CTLR(DT_DRV_INST(0)))};
+
+static const struct bvd_config bvd_cfg = {
+    .io_channel =
+        {
+            DT_IO_CHANNELS_INPUT(DT_DRV_INST(0)),
+        },
+#if DT_INST_NODE_HAS_PROP(0, power_gpios)
+    .power = GPIO_DT_SPEC_INST_GET(0, power_gpios),
+#endif
+    .output_ohm = DT_INST_PROP(0, output_ohms),
+    .full_ohm = DT_INST_PROP(0, full_ohms),
+};
+
+DEVICE_DT_INST_DEFINE(0, &bvd_init, NULL, &bvd_data, &bvd_cfg, POST_KERNEL,
+                      CONFIG_SENSOR_INIT_PRIORITY, &bvd_api);