qmk_firmware/keyboard/hhkb_rn42/rn42/battery.c

#include <avr/io.h>
#include <util/delay.h>
#include "battery.h"


/*
 * Battery
 */
void battery_init(void)
{
    // blink 
    battery_led(LED_ON);  _delay_ms(500);
    battery_led(LED_OFF); _delay_ms(500);
    battery_led(LED_ON);  _delay_ms(500);
    battery_led(LED_OFF); _delay_ms(500);
    // LED indicates charger status
    battery_led(LED_CHARGER);

    // ADC setting for voltage monitor
    // Ref:2.56V band-gap, Input:ADC0(PF0), Prescale:128(16MHz/128=125KHz)
    ADMUX = (1<<REFS1) | (1<<REFS0);
    ADCSRA = (1<<ADPS2) | (1<<ADPS1) | (1<<ADPS0);
    ADCSRA |= (1<<ADEN);
}

// Indicator for battery
void battery_led(battery_led_t val)
{
    if (val == LED_TOGGLE) {
        // Toggle LED
        DDRF  |=  (1<<5);
        PINF  |=  (1<<5);
    } else if (val == LED_ON) {
        // On overriding charger status
        DDRF  |=  (1<<5);
        PORTF &= ~(1<<5);
    } else if (val == LED_OFF) {
        // Off overriding charger status
        DDRF  |=  (1<<5);
        PORTF |=  (1<<5);
    } else {
        // Display charger status
        DDRF  &= ~(1<<5);
        PORTF &= ~(1<<5);
    }
}

bool battery_charging(void)
{
    if (!(USBSTA&(1<<VBUS))) return false;

    // Charger Status:
    //   MCP73831   MCP73832   LTC4054  Status
    //   Hi-Z       Hi-Z       Hi-Z     Shutdown/No Battery
    //   Low        Low        Low      Charging
    //   Hi         Hi-Z       Hi-Z     Charged

    // preserve last register status
    uint8_t ddrf_prev  = DDRF;
    uint8_t portf_prev = PORTF;

    // Input with pullup
    DDRF  &= ~(1<<5);
    PORTF |=  (1<<5);
    _delay_ms(1);
    bool charging = PINF&(1<<5) ? false : true;

    // restore last register status
    DDRF  = (DDRF&~(1<<5))  | (ddrf_prev&(1<<5));
    PORTF = (PORTF&~(1<<5)) | (portf_prev&(1<<5));

    // TODO: With MCP73831 this can not get stable status when charging.
    // LED is powered from PSEL line(USB or Lipo)
    // due to weak low output of STAT pin?
    // due to pull-up'd via resitor and LED?
    return charging;
}

// Returns voltage in mV
uint16_t battery_voltage(void)
{
    volatile uint16_t bat;
    //ADCSRA |= (1<<ADEN);

    // discard first result
    ADCSRA |= (1<<ADSC);
    while (ADCSRA & (1<<ADSC)) ;
    bat = ADC;

    // discard second result
    ADCSRA |= (1<<ADSC);
    while (ADCSRA & (1<<ADSC)) ;
    bat = ADC;

    ADCSRA |= (1<<ADSC);
    while (ADCSRA & (1<<ADSC)) ;
    bat = ADC;

    //ADCSRA &= ~(1<<ADEN);

    return (bat - BATTERY_ADC_OFFSET) * BATTERY_ADC_RESOLUTION;
}

static bool low_voltage(void) {
    static bool low = false;
    uint16_t v = battery_voltage();
    if (v < BATTERY_VOLTAGE_LOW_LIMIT) {
        low = true;
    } else if (v > BATTERY_VOLTAGE_LOW_RECOVERY) {
        low = false;
    }
    return low;
}

battery_status_t battery_status(void)
{
    if (USBSTA&(1<<VBUS)) {
        /* powered */
        return battery_charging() ? CHARGING : FULL_CHARGED;
    } else {
        /* not powered */
        return low_voltage() ? LOW_VOLTAGE : DISCHARGING;
    }
}