qmk_firmware/drivers/avr/analog.c

/* Copyright 2015 Jack Humbert
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

// Simple analog to digitial conversion

#include <avr/io.h>
#include <avr/pgmspace.h>
#include <stdint.h>
#include "analog.h"

static uint8_t aref = (1 << REFS0);  // default to AREF = Vcc

void analogReference(uint8_t mode) { aref = mode & 0xC0; }

// Arduino compatible pin input
int16_t analogRead(uint8_t pin) {
#if defined(__AVR_ATmega32U4__)
    static const uint8_t PROGMEM pin_to_mux[] = {0x00, 0x01, 0x04, 0x05, 0x06, 0x07, 0x25, 0x24, 0x23, 0x22, 0x21, 0x20};
    if (pin >= 12) return 0;
    return adc_read(pgm_read_byte(pin_to_mux + pin));
#elif defined(__AVR_AT90USB646__) || defined(__AVR_AT90USB1286__)
    if (pin >= 8) return 0;
    return adc_read(pin);
#else
    return 0;
#endif
}

// Mux input
int16_t adc_read(uint8_t mux) {
#if defined(__AVR_AT90USB162__)
    return 0;
#else
    uint8_t low;

    ADCSRA = (1 << ADEN) | ADC_PRESCALER;                // enable ADC
    ADCSRB = (1 << ADHSM) | (mux & 0x20);                // high speed mode
    ADMUX  = aref | (mux & 0x1F);                        // configure mux input
    ADCSRA = (1 << ADEN) | ADC_PRESCALER | (1 << ADSC);  // start the conversion
    while (ADCSRA & (1 << ADSC))
        ;                      // wait for result
    low = ADCL;                // must read LSB first
    return (ADCH << 8) | low;  // must read MSB only once!
#endif
}