File content as of revision 7:acf82069b794:

/*
 * Mbed library program
 *  Control Piezo Transducer
 *
 * Copyright (c) 2018 Kenji Arai / JH1PJL
 *  http://www.page.sannet.ne.jp/kenjia/index.html
 *  http://mbed.org/users/kenjiArai/
 *      Created:    Feburary  28th, 2018
 *      Revised:    March      3rd, 2018
 */

#include "mbed.h"
#include "piezo_bz.h"

PIEZO_BZ::PIEZO_BZ(PinName pin, uint32_t f, uint32_t on_off_time)
    :  _pin(pin)
{
    out = false;
    _pin.write(0);
    freq = f;
    if (freq < 50) {
        freq = 50;
    } else if (freq > 10000) {
        freq = 10000;
    }
    flag_run = false;
    _t0.attach_us(callback(this, &PIEZO_BZ::create_freq_irq), 500000 / freq);
    t_onoff  = on_off_time;
    if (t_onoff == 0) {
        flag_continuous = true;
        _t1.attach_us(
            callback(this, &PIEZO_BZ::create_onoff_irq),
            1000000000 // 1000sec
        );
    } else {
        flag_continuous = false;
        _t1.attach_us(
            callback(this, &PIEZO_BZ::create_onoff_irq),
            t_onoff * 1000
        );
    }
}

PIEZO_BZ::~PIEZO_BZ()
{
    _t0.detach();
    _t1.detach();
}

void PIEZO_BZ::start()
{
    flag_run = true;
}

void PIEZO_BZ::stop()
{
    flag_run = false;
}

void PIEZO_BZ::change_frequency(uint32_t f)
{
    _t0.detach();
    freq = f;
    if (freq < 300) {
        freq = 300;
    } else if (freq > 10000) {
        freq = 10000;
    }
    _t0.attach_us(callback(this, &PIEZO_BZ::create_freq_irq), 500000 / freq);
}

void PIEZO_BZ::change_on_off(uint32_t on_off_time)
{
    _t1.detach();
    t_onoff  = on_off_time;
    if (t_onoff == 0) {
        flag_continuous = true;
        _t1.attach_us(
            callback(this, &PIEZO_BZ::create_onoff_irq),
            1000000000U // 1000sec
        );
    } else {
        flag_continuous = false;
        _t1.attach_us(
            callback(this, &PIEZO_BZ::create_onoff_irq),
            t_onoff * 1000U
        );
    }
}

void PIEZO_BZ::create_freq_irq(void)
{
    // <point A>
    if (!flag_run) {
        _pin.write(0);
        return;
    }
    if (!flag_continuous) {
        if (!flag_onoff) {
            _pin.write(0);
            return;
        }
    }
    _pin.write(out);
    out = !out;
    // <point B>
    // Processing time from <point A> to <point B> is 200 to 230ns
    // measured on Nucleo-F446RE board (System clock 180MHz)
}

void PIEZO_BZ::create_onoff_irq(void)
{
    // <point C>
    if (flag_continuous) {
        flag_onoff = true;
    } else {
        flag_onoff = !flag_onoff;
    }
    // <point D>
    // Processing time from <point C> to <point D> is 120 to 140ns
    // measured on Nucleo-F446RE board (System clock 180MHz)
}