ADCMux.hpp

#ifndef __ADCMUX_HPP__
#define __ADCMUX_HPP__

#include <Arduino.h>

#include <cstdarg>

extern "C" int system_adc_read();

#ifndef ADC_RESOLUTION_BITS
#define ADC_RESOLUTION_BITS (10) // hardware ADC resolution
#endif

template <
    int8_t PIN1 = NOT_A_PIN, int8_t PIN2 = NOT_A_PIN, int8_t PIN3 = NOT_A_PIN, int8_t PIN4 = NOT_A_PIN,
    int8_t PIN5 = NOT_A_PIN, int8_t PIN6 = NOT_A_PIN, int8_t PIN7 = NOT_A_PIN, int8_t PIN8 = NOT_A_PIN
> class ADCMux {
public:
    void init() {
        _initPin<PIN1, PIN1>()();
        _initPin<PIN2, PIN2>()();
        _initPin<PIN3, PIN3>()();
        _initPin<PIN4, PIN4>()();
        _initPin<PIN5, PIN5>()();
        _initPin<PIN6, PIN6>()();
        _initPin<PIN7, PIN7>()();
        _initPin<PIN8, PIN8>()();
    }

    int analogRead(uint8_t channel, uint8_t oversample_bits = ADC_RESOLUTION_BITS) {
        _selectPin<PIN1, 0x01 << 0>()(channel);
        _selectPin<PIN2, 0x01 << 1>()(channel);
        _selectPin<PIN3, 0x01 << 2>()(channel);
        _selectPin<PIN4, 0x01 << 3>()(channel);
        _selectPin<PIN5, 0x01 << 4>()(channel);
        _selectPin<PIN6, 0x01 << 5>()(channel);
        _selectPin<PIN7, 0x01 << 6>()(channel);
        _selectPin<PIN8, 0x01 << 7>()(channel);

        size_t loop = 0;
        if (oversample_bits > ADC_RESOLUTION_BITS)
            loop = oversample_bits - ADC_RESOLUTION_BITS;
        loop = 0x01 << loop;

        // clear out the SAR ADC capacitor by reading it once
        system_adc_read();

        int result = 0;
        noInterrupts();
        for (int i = 0;i < loop;++i)
            result += system_adc_read();
        interrupts();
        return result;
    }
private:
    template <int8_t PIN, uint32_t MASK>
    class _selectPin {
    public:
        void operator()(uint8_t channel) {
#ifdef DEBUG_ADCMUX
            Serial.printf("_selectPin(): PIN = %d, MASK = 0x%08x, channel = %d\n", PIN, MASK, channel);
#endif
            digitalWrite(PIN, channel & MASK ? HIGH : LOW);
        }
    };

    // dunno why I can't specialize with `template <>`, so this UNUSED is here.
    template <int8_t PIN, int8_t UNUSED>
    class _initPin {
    public:
        void operator()() {
#ifdef DEBUG_ADCMUX
            Serial.printf("_initPin(): pinMode(%d, OUTPUT);\n", PIN);
#endif
            pinMode(PIN, OUTPUT);
        }
    };
};

template <int8_t PIN1, int8_t PIN2, int8_t PIN3, int8_t PIN4, int8_t PIN5, int8_t PIN6, int8_t PIN7, int8_t PIN8>
template <uint32_t MASK>
class ADCMux<PIN1, PIN2, PIN3, PIN4, PIN5, PIN6, PIN7, PIN8>::_selectPin<NOT_A_PIN, MASK> {
public:
    void operator()(uint8_t channel) {}
};

template <int8_t PIN1, int8_t PIN2, int8_t PIN3, int8_t PIN4, int8_t PIN5, int8_t PIN6, int8_t PIN7, int8_t PIN8>
template <int8_t UNUSED>
class ADCMux<PIN1, PIN2, PIN3, PIN4, PIN5, PIN6, PIN7, PIN8>::_initPin<NOT_A_PIN, UNUSED> {
public:
    void operator()() {}
};

#endif