Source: arts/audiosubsys.h

    /*

    Copyright (C) 2000 Stefan Westerfeld
                       stefan@space.twc.de

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.
  
    This library 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
    Library General Public License for more details.
   
    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
    Boston, MA 02111-1307, USA.

    */

#ifndef AUDIOSUBSYS_H
#define AUDIOSUBSYS_H
#include <string>
#include "pipebuffer.h"
#include "startupmanager.h"

/*
 * BC - Status (2000-09-30): AudioSubSystem, ASProducer, ASConsumer.
 *
 * These classes are kept binary compatible. You can rely on them.
 * AudioSubSystem has a private data pointer to do so. Even if ports to
 * other architectures or hardware will require different organization
 * (i.e. no fragments, direct memory access via mmap), the data members
 * and functions exported here MAY NOT BE CHANGED. Use the private data
 * pointer for adding data members.
 *
 * If ASProducer/ASConsumer doesn't suit the needs any longer, do NOT
 * change them. Add new classes instead.
 */

namespace Arts {

class ASProducer {
public:
	virtual void needMore() = 0;
};

// FIXME: haveMore won't be called currently
class ASConsumer {
public:
	virtual void haveMore() = 0;
};

class AudioSubSystemStart :public StartupClass {
protected:
	class AudioSubSystem *_instance;
public:
	inline AudioSubSystem *the() { return _instance; };
	void startup();
	void shutdown();
};

class AudioSubSystemPrivate;

class AudioSubSystem {
	class AudioSubSystemPrivate *d;

	std::string _error;
	int audio_fd;
	char *fragment_buffer;
	int usageCount;

	int _fragmentCount;
	int _fragmentSize;
	int _samplingRate;
	int _channels;

	bool _running;
	bool _fullDuplex;
	PipeBuffer wBuffer, rBuffer;
	ASConsumer *consumer;
	ASProducer *producer;

	friend class AudioSubSystemStart;
	AudioSubSystem();
	~AudioSubSystem();

	void close();
	void initAudioIO();

public:
	enum { ioRead=1, ioWrite=2, ioExcept=4 };

	// singleton
	static AudioSubSystem *the();

	/*
	 * Currently, if you want to use the AudioSubSystem, you need to
	 * 
	 * 1. - attach one producer
	 *    - attach one consumer (only for full duplex)
	 *    - open the audio subsystem using open (watch the fd)
	 *    (in any order)
	 *
	 * 2. react on the callbacks you get for the producer
	 *
	 * 3. if you don't need the audio subsystem any longer, call detach
	 *    both, the producer and the cosumer.
	 *
	 * Be careful that you don't read/write from/to the audio subsystem
	 * when running() is not true.
	 */

	bool attachProducer(ASProducer *producer);
	bool attachConsumer(ASConsumer *consumer);

	void detachProducer();
	void detachConsumer();

	/*
	 * can be used to select the AudioIO class to use, reasonable choices
	 * may be "oss" or "alsa" at this point in time - you need to choose
	 * this before doing anything else
	 */
	void audioIO(const std::string& audioIO);
	std::string audioIO();

	// which device to use for audio output (default /dev/dsp)
	void deviceName(const std::string& deviceName);
	std::string deviceName();

	void fragmentSize(int size);
	int fragmentSize();

	void fragmentCount(int fragments);
	int fragmentCount();

	void samplingRate(int samplingrate);
	int samplingRate();

	void channels(int channels);
	int channels();

	void format(int format);
	int format();

	void fullDuplex(bool newFullDuplex);
	bool fullDuplex();

	bool check();

	int open();								/* obsolete: see bool open(); */
	const char *error();

	/*
	 * returncode of open: -1 indicates an error; otherwise, the returned
	 * filedescriptor must be watched using select calls, and, whenever
	 * fd is ready for something, handleIO must be called. 
	 *
	 * The type for handleIO must be set to ioRead if fd is ready for
	 * reading, ioWrite if fd is ready for writing, ioExcept if something
	 * special happend or any combination of these using bitwise or.
	 */

	void handleIO(int type);

	/*
	 * the old open function didn't cover cases where the audio driver will
	 * not be able to provide a file decriptor - it is left for compatibility
	 * reasons, you should use the bool variant instead
	 */
	bool open(int& fd);

	void read(void *buffer, int size);
	void write(void *buffer, int size);

	/**
	 * returns true as long as the audio subsystem is opened and active (that
	 * is, between successful opening, with attaching producer, and the first
	 * detachConsumer/detachProducer)
	 */
	bool running();

	/*
	 * returns true if the audiosubsystem would like to have the CPU now
	 * and not later ;-)
	 */
	bool needCPU();
};

};

#endif /* AUDIOSUBSYS_H */