native_sound_timer.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * 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 3 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/>.
 *
 */

#ifndef MADS_CORE_NATIVE_SOUND_TIMER_H
#define MADS_CORE_NATIVE_SOUND_TIMER_H

#include "common/scummsys.h"

namespace MADS {

class NativeSoundTimer {
public:
    enum {
        kPitClockHz = 1193182,
        kHostTimerDivisor = 0x07a8,
        kHostServiceDivider = 2,
        kSequenceServiceDivider = 5
    };

    NativeSoundTimer() : _accumulator(0), _pollCountdown(1) {
    }

    uint32 advance(uint64 elapsedUnits, uint64 unitsPerSecond) {
        const uint64 serviceThreshold = unitsPerSecond *
            kHostTimerDivisor * kHostServiceDivider;

        _accumulator += elapsedUnits * kPitClockHz;
        const uint32 serviceTicks = _accumulator / serviceThreshold;
        _accumulator %= serviceThreshold;
        return serviceTicks;
    }

    bool pollDue() {
        if (--_pollCountdown)
            return false;

        _pollCountdown = kSequenceServiceDivider;
        return true;
    }

private:
    uint64 _accumulator;
    byte _pollCountdown;
};

} // namespace MADS

#endif