zmk_mf68/app/drivers/zephyr/battery_voltage_divider.c

/*
 * Copyright (c) 2020 The ZMK Contributors
 *
 * SPDX-License-Identifier: MIT
 */

#define DT_DRV_COMPAT zmk_battery_voltage_divider

#include <device.h>
#include <drivers/kscan.h>
#include <drivers/gpio.h>
#include <drivers/adc.h>
#include <drivers/sensor.h>
#include <logging/log.h>
#include <math.h>

LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);

#if DT_HAS_COMPAT_STATUS_OKAY(DT_DRV_COMPAT)

#define VBATT DT_PATH(vbatt)

struct battery_config {
    struct device *adc;
    struct adc_channel_cfg acc;
    struct adc_sequence as;
    int16_t adc_raw;
};

static struct battery_config battery_config;

static int lithium_ion_mv_to_pct(int16_t bat_mv) {
    // Magic function that maps mV to this discharge graph from adafruit:
    // https://learn.adafruit.com/li-ion-and-lipoly-batteries/voltages
    return round(106.818 +
                 (-0.032685 - 106.818) / pow(1 + pow(bat_mv / 3679.35, 58.979), 0.347386));
}

static void battery_read(struct k_work *workd) {
    struct battery_config *cfg = &battery_config;
    struct adc_sequence *as = &cfg->as;

    int rc = adc_read(cfg->adc, as);
    as->calibrate = false;
    if (rc == 0) {
        int32_t val = cfg->adc_raw;

        adc_raw_to_millivolts(adc_ref_internal(cfg->adc), cfg->acc.gain, as->resolution, &val);

        rc = val * (uint64_t)DT_PROP(VBATT, full_ohms) / DT_PROP(VBATT, output_ohms);
        LOG_DBG("ADC raw %d ~ %d mV => %d mV\n", cfg->adc_raw, val, rc);
        int percent = lithium_ion_mv_to_pct(rc);
        LOG_DBG("Percent: %d", percent);
    } else {
        LOG_DBG("Failed to read ADC: %d", rc);
    }
}

K_WORK_DEFINE(battery_work, battery_read);

static void battery_handler(struct k_timer *timer) { k_work_submit(&battery_work); }

K_TIMER_DEFINE(battery_tick, battery_handler, NULL);

static int battery_setup(struct device *_arg) {
    struct battery_config *cfg = &battery_config;
    struct adc_sequence *as = &cfg->as;
    struct adc_channel_cfg *acc = &cfg->acc;

    cfg->adc = device_get_binding(DT_IO_CHANNELS_LABEL(VBATT));

    if (cfg->adc == NULL) {
        LOG_ERR("ADC %s failed to retrieve", DT_IO_CHANNELS_LABEL(VBATT));
        return -ENOENT;
    }

    *as = (struct adc_sequence){
        .channels = BIT(0),
        .buffer = &cfg->adc_raw,
        .buffer_size = sizeof(cfg->adc_raw),
        .oversampling = 4,
        .calibrate = true,
    };

#ifdef CONFIG_ADC_NRFX_SAADC
    *acc = (struct adc_channel_cfg){
        .gain = ADC_GAIN_1_5,
        .reference = ADC_REF_INTERNAL,
        .acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 40),
        .input_positive = SAADC_CH_PSELP_PSELP_AnalogInput0 + DT_IO_CHANNELS_INPUT(VBATT),
    };

    as->resolution = 12;
#else
#error Unsupported ADC
#endif

    int adc_rc = adc_channel_setup(cfg->adc, acc);
    LOG_DBG("AIN%u setup returned %d", DT_IO_CHANNELS_INPUT(VBATT), adc_rc);

    if (adc_rc != 0) {
        return adc_rc;
    }

    k_timer_start(&battery_tick, K_NO_WAIT, K_SECONDS(5));

    return 0;
}

SYS_INIT(battery_setup, APPLICATION, CONFIG_APPLICATION_INIT_PRIORITY);

#endif /* DT_HAS_COMPAT_STATUS_OKAY(DT_DRV_COMPAT) */