File content as of revision 2:8dff77a1ee4d:

#include "mbed.h"
#include "rtos.h"

#define TITLE_STR1      ("KIK01 Kick Machine")
#define TITLE_STR2      ("20170604")

#define PI_F            (3.1415926f)
#define SAMPLING_RATE   (96000)
#define SAMPLING_PERIOD (1.0f/SAMPLING_RATE)

#define ENVELOPE_PERIOD     (500)
#define FREQUENCY_ATTACK    (5)
#define FREQUENCY_RELEASE   (300)
#define AMPLITUDE_ATTACK    (50)
#define AMPLITUDE_RELEASE   (200)

AnalogOut Dac1(PA_4);

class EnvelopeAR {
public:
    EnvelopeAR(int _attack, int _release, float _v0, float _v1, float _v2, float _attackTauRatio=0.36f, float _releaseTauRatio=0.36f) :
        amplitude(_v0),
        v0(_v0),
        v1(_v1),
        v2(_v2),
        vLast(_v0),
        attackTauRatio(_attackTauRatio),
        releaseTauRatio(_releaseTauRatio)
    {
        setAttack(_attack);
        setRelease(_release);
    }

    ~EnvelopeAR() {}

    void setAttack(int _attack) {
        attack = _attack;
        tau0 = attack * attackTauRatio;
    }
    int getAttack() { return attack; }

    void setRelease(int _release) {
        release = _release;
        tau1 = release * releaseTauRatio;
    }
    int getRelease() { return release; }

    void setAttackTauRatio(float _attackTauRatio) { attackTauRatio = _attackTauRatio; }
    float getAttackTauRatio() { return attackTauRatio;  }

    void setReleaseTauRatio(float _releaseTauRatio) { releaseTauRatio = _releaseTauRatio; }
    float getReleaseTauRatio() { return releaseTauRatio; }

    void setV0(float _v0) { v0 = _v0; }
    float getV0() { return v0; }
    void setV1(float _v1) { v1 = _v1; }
    float getV1() { return v1; }
    void setV2(float _v2) { v2 = _v2; }
    float getV2() { return v2; }

    float getAmplitude() { return amplitude; }
    float getAmplitude(int tick) {
        if (tick < attack) {
            // attackの処理
            amplitude = v0 + (v1 - v0) * (1 - expf(-(float)tick / tau0));
            vLast = amplitude;
        }
        else {
            // releaseの処理
            amplitude = (vLast - v2) * (expf(-(float)(tick - attack) / tau1)) + v2;
        }
        return amplitude;
    }

private:
    int attack;
    int release;
    float amplitude;
    float v0;
    float v1;
    float v2;
    float vLast;
    float tau0;
    float tau1;
    float attackTauRatio;
    float releaseTauRatio;
};

EnvelopeAR envelopeFrequency(
    FREQUENCY_ATTACK, FREQUENCY_RELEASE, 880.0f, 120.0f, 40.0f, 0.36f, 0.1f);
EnvelopeAR envelopeAmplitude(AMPLITUDE_ATTACK, AMPLITUDE_RELEASE, 0.9f, 1.0f, 0.0f);

int ticks;
int envelopeTicks;
float frequency;
float phi;
float phiDelta;
float amplitude;

void generateWave()
{
    phi += phiDelta;
    if (phi >= 1.0f) {
        phi -= 2.0f;
    }
    float level = sinf(PI_F * phi) * amplitude;

    Dac1.write((level + 1.0f) / 2.0f);
}

void generateEnvelope()
{
    // Frequency Envelope
    frequency = envelopeFrequency.getAmplitude(envelopeTicks);
    phiDelta = 2.0f * frequency / SAMPLING_RATE;

    // Amplitude Envelope
    amplitude = envelopeAmplitude.getAmplitude(envelopeTicks);

    envelopeTicks++;
    if (envelopeTicks == ENVELOPE_PERIOD) {
        envelopeTicks = 0;
    }
}

void update()
{
    ticks--;
    if (ticks == 0) {
        ticks = SAMPLING_RATE / 1000;
        generateEnvelope();
    }
    generateWave();
}

int main()
{
    printf("%s %s\r\n", TITLE_STR1, TITLE_STR2);
    
    frequency = 1000.0f;
    phiDelta = 2.0f * frequency / SAMPLING_RATE;
    amplitude = 1.0f;
    
    ticks = SAMPLING_RATE / 1000;
    envelopeTicks = 0;
    
    Ticker samplingTicker;
    samplingTicker.attach(&update, SAMPLING_PERIOD);
        
    for (;;) {}
}