src/audio/dma/SDL_dmaaudio.c - third_party/sdl - Git at Google

 /*
     SDL - Simple DirectMedia Layer
     Copyright (C) 1997-2009 Sam Lantinga

     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Lesser General Public
     License as published by the Free Software Foundation; either
     version 2.1 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
     Lesser General Public License for more details.

     You should have received a copy of the GNU Lesser General Public
     License along with this library; if not, write to the Free Software
     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

     Sam Lantinga
     slouken@libsdl.org
 */
 #include "SDL_config.h"

 /* Allow access to a raw mixing buffer */

 #include <stdio.h>
 #include <string.h>	/* For strerror() */
 #include <errno.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <sys/types.h>
 #include <sys/time.h>
 #include <sys/ioctl.h>
 #include <sys/stat.h>
 #include <sys/mman.h>

 #if SDL_AUDIO_DRIVER_OSS_SOUNDCARD_H
 /* This is installed on some systems */
 #include <soundcard.h>
 #else
 /* This is recommended by OSS */
 #include <sys/soundcard.h>
 #endif

 #ifndef MAP_FAILED
 #define MAP_FAILED	((Uint8 *)-1)
 #endif

 #include "SDL_timer.h"
 #include "SDL_audio.h"
 #include "../SDL_audio_c.h"
 #include "../SDL_audiodev_c.h"
 #include "SDL_dmaaudio.h"

 /* The tag name used by DMA audio */
 #define DMA_DRIVER_NAME         "dma"

 /* Open the audio device for playback, and don't block if busy */
 #define OPEN_FLAGS	(O_RDWR|O_NONBLOCK)

 /* Audio driver functions */
 static int DMA_OpenAudio(_THIS, SDL_AudioSpec *spec);
 static void DMA_WaitAudio(_THIS);
 static void DMA_PlayAudio(_THIS);
 static Uint8 *DMA_GetAudioBuf(_THIS);
 static void DMA_CloseAudio(_THIS);

 /* Audio driver bootstrap functions */

 static int Audio_Available(void)
 {
 	int available;
 	int fd;

 	available = 0;

 	fd = SDL_OpenAudioPath(NULL, 0, OPEN_FLAGS, 0);
 	if ( fd >= 0 ) {
 		int caps;
 		struct audio_buf_info info;

 		if ( (ioctl(fd, SNDCTL_DSP_GETCAPS, &caps) == 0) &&
 	             (caps & DSP_CAP_TRIGGER) && (caps & DSP_CAP_MMAP) &&
 		     (ioctl(fd, SNDCTL_DSP_GETOSPACE, &info) == 0) ) {
 			available = 1;
 		}
 		close(fd);
 	}
 	return(available);
 }

 static void Audio_DeleteDevice(SDL_AudioDevice *device)
 {
 	SDL_free(device->hidden);
 	SDL_free(device);
 }

 static SDL_AudioDevice *Audio_CreateDevice(int devindex)
 {
 	SDL_AudioDevice *this;

 	/* Initialize all variables that we clean on shutdown */
 	this = (SDL_AudioDevice *)SDL_malloc(sizeof(SDL_AudioDevice));
 	if ( this ) {
 		SDL_memset(this, 0, (sizeof *this));
 		this->hidden = (struct SDL_PrivateAudioData *)
 				SDL_malloc((sizeof *this->hidden));
 	}
 	if ( (this == NULL) || (this->hidden == NULL) ) {
 		SDL_OutOfMemory();
 		if ( this ) {
 			SDL_free(this);
 		}
 		return(0);
 	}
 	SDL_memset(this->hidden, 0, (sizeof *this->hidden));
 	audio_fd = -1;

 	/* Set the function pointers */
 	this->OpenAudio = DMA_OpenAudio;
 	this->WaitAudio = DMA_WaitAudio;
 	this->PlayAudio = DMA_PlayAudio;
 	this->GetAudioBuf = DMA_GetAudioBuf;
 	this->CloseAudio = DMA_CloseAudio;

 	this->free = Audio_DeleteDevice;

 	return this;
 }

 AudioBootStrap DMA_bootstrap = {
 	DMA_DRIVER_NAME, "OSS /dev/dsp DMA audio",
 	Audio_Available, Audio_CreateDevice
 };

 /* This function waits until it is possible to write a full sound buffer */
 static void DMA_WaitAudio(_THIS)
 {
 	fd_set fdset;

 	/* Check to see if the thread-parent process is still alive */
 	{ static int cnt = 0;
 		/* Note that this only works with thread implementations
 		   that use a different process id for each thread.
 		*/
 		if (parent && (((++cnt)%10) == 0)) { /* Check every 10 loops */
 			if ( kill(parent, 0) < 0 ) {
 				this->enabled = 0;
 			}
 		}
 	}

 	/* See if we need to use timed audio synchronization */
 	if ( frame_ticks ) {
 		/* Use timer for general audio synchronization */
 		Sint32 ticks;

 		ticks = ((Sint32)(next_frame - SDL_GetTicks()))-FUDGE_TICKS;
 		if ( ticks > 0 ) {
 			SDL_Delay(ticks);
 		}
 	} else {
 		/* Use select() for audio synchronization */
 		struct timeval timeout;
 		FD_ZERO(&fdset);
 		FD_SET(audio_fd, &fdset);
 		timeout.tv_sec = 10;
 		timeout.tv_usec = 0;
 #ifdef DEBUG_AUDIO
 		fprintf(stderr, "Waiting for audio to get ready\n");
 #endif
 		if ( select(audio_fd+1, NULL, &fdset, NULL, &timeout) <= 0 ) {
 			const char *message =
 #ifdef AUDIO_OSPACE_HACK
 			"Audio timeout - buggy audio driver? (trying ospace)";
 #else
 			"Audio timeout - buggy audio driver? (disabled)";
 #endif
 			/* In general we should never print to the screen,
 			   but in this case we have no other way of letting
 			   the user know what happened.
 			*/
 			fprintf(stderr, "SDL: %s\n", message);
 #ifdef AUDIO_OSPACE_HACK
 			/* We may be able to use GET_OSPACE trick */
 			frame_ticks = (float)(this->spec->samples*1000) /
 			                      this->spec->freq;
 			next_frame = SDL_GetTicks()+frame_ticks;
 #else
 			this->enabled = 0;
 			/* Don't try to close - may hang */
 			audio_fd = -1;
 #ifdef DEBUG_AUDIO
 			fprintf(stderr, "Done disabling audio\n");
 #endif
 #endif /* AUDIO_OSPACE_HACK */
 		}
 #ifdef DEBUG_AUDIO
 		fprintf(stderr, "Ready!\n");
 #endif
 	}
 }

 static void DMA_PlayAudio(_THIS)
 {
 	/* If timer synchronization is enabled, set the next write frame */
 	if ( frame_ticks ) {
 		next_frame += frame_ticks;
 	}
 	return;
 }

 static Uint8 *DMA_GetAudioBuf(_THIS)
 {
 	count_info info;
 	int playing;
 	int filling;

 	/* Get number of blocks, looping if we're not using select() */
 	do {
 		if ( ioctl(audio_fd, SNDCTL_DSP_GETOPTR, &info) < 0 ) {
 			/* Uh oh... */
 			this->enabled = 0;
 			return(NULL);
 		}
 	} while ( frame_ticks && (info.blocks < 1) );
 #ifdef DEBUG_AUDIO
 	if ( info.blocks > 1 ) {
 		printf("Warning: audio underflow (%d frags)\n", info.blocks-1);
 	}
 #endif
 	playing = info.ptr / this->spec.size;
 	filling = (playing + 1)%num_buffers;
 	return (dma_buf + (filling * this->spec.size));
 }

 static void DMA_CloseAudio(_THIS)
 {
 	if ( dma_buf != NULL ) {
 		munmap(dma_buf, dma_len);
 		dma_buf = NULL;
 	}
 	if ( audio_fd >= 0 ) {
 		close(audio_fd);
 		audio_fd = -1;
 	}
 }

 static int DMA_ReopenAudio(_THIS, const char *audiodev, int format, int stereo,
 							SDL_AudioSpec *spec)
 {
 	int frag_spec;
 	int value;

 	/* Close and then reopen the audio device */
 	close(audio_fd);
 	audio_fd = open(audiodev, O_RDWR, 0);
 	if ( audio_fd < 0 ) {
 		SDL_SetError("Couldn't open %s: %s", audiodev, strerror(errno));
 		return(-1);
 	}

 	/* Calculate the final parameters for this audio specification */
 	SDL_CalculateAudioSpec(spec);

 	/* Determine the power of two of the fragment size */
 	for ( frag_spec = 0; (0x01<<frag_spec) < spec->size; ++frag_spec );
 	if ( (0x01<<frag_spec) != spec->size ) {
 		SDL_SetError("Fragment size must be a power of two");
 		return(-1);
 	}

 	/* Set the audio buffering parameters */
 	if ( ioctl(audio_fd, SNDCTL_DSP_SETFRAGMENT, &frag_spec) < 0 ) {
 		SDL_SetError("Couldn't set audio fragment spec");
 		return(-1);
 	}

 	/* Set the audio format */
 	value = format;
 	if ( (ioctl(audio_fd, SNDCTL_DSP_SETFMT, &value) < 0) ||
 						(value != format) ) {
 		SDL_SetError("Couldn't set audio format");
 		return(-1);
 	}

 	/* Set mono or stereo audio */
 	value = (spec->channels > 1);
 	if ( (ioctl(audio_fd, SNDCTL_DSP_STEREO, &stereo) < 0) ||
 						(value != stereo) ) {
 		SDL_SetError("Couldn't set audio channels");
 		return(-1);
 	}

 	/* Set the DSP frequency */
 	value = spec->freq;
 	if ( ioctl(audio_fd, SNDCTL_DSP_SPEED, &value) < 0 ) {
 		SDL_SetError("Couldn't set audio frequency");
 		return(-1);
 	}
 	spec->freq = value;

 	/* We successfully re-opened the audio */
 	return(0);
 }

 static int DMA_OpenAudio(_THIS, SDL_AudioSpec *spec)
 {
 	char audiodev[1024];
 	int format;
 	int stereo;
 	int value;
 	Uint16 test_format;
 	struct audio_buf_info info;

 	/* Reset the timer synchronization flag */
 	frame_ticks = 0.0;

 	/* Open the audio device */
 	audio_fd = SDL_OpenAudioPath(audiodev, sizeof(audiodev), OPEN_FLAGS, 0);
 	if ( audio_fd < 0 ) {
 		SDL_SetError("Couldn't open %s: %s", audiodev, strerror(errno));
 		return(-1);
 	}
 	dma_buf = NULL;
 	ioctl(audio_fd, SNDCTL_DSP_RESET, 0);

 	/* Get a list of supported hardware formats */
 	if ( ioctl(audio_fd, SNDCTL_DSP_GETFMTS, &value) < 0 ) {
 		SDL_SetError("Couldn't get audio format list");
 		return(-1);
 	}

 	/* Try for a closest match on audio format */
 	format = 0;
 	for ( test_format = SDL_FirstAudioFormat(spec->format);
 						! format && test_format; ) {
 #ifdef DEBUG_AUDIO
 		fprintf(stderr, "Trying format 0x%4.4x\n", test_format);
 #endif
 		switch ( test_format ) {
 			case AUDIO_U8:
 				if ( value & AFMT_U8 ) {
 					format = AFMT_U8;
 				}
 				break;
 			case AUDIO_S8:
 				if ( value & AFMT_S8 ) {
 					format = AFMT_S8;
 				}
 				break;
 			case AUDIO_S16LSB:
 				if ( value & AFMT_S16_LE ) {
 					format = AFMT_S16_LE;
 				}
 				break;
 			case AUDIO_S16MSB:
 				if ( value & AFMT_S16_BE ) {
 					format = AFMT_S16_BE;
 				}
 				break;
 			case AUDIO_U16LSB:
 				if ( value & AFMT_U16_LE ) {
 					format = AFMT_U16_LE;
 				}
 				break;
 			case AUDIO_U16MSB:
 				if ( value & AFMT_U16_BE ) {
 					format = AFMT_U16_BE;
 				}
 				break;
 			default:
 				format = 0;
 				break;
 		}
 		if ( ! format ) {
 			test_format = SDL_NextAudioFormat();
 		}
 	}
 	if ( format == 0 ) {
 		SDL_SetError("Couldn't find any hardware audio formats");
 		return(-1);
 	}
 	spec->format = test_format;

 	/* Set the audio format */
 	value = format;
 	if ( (ioctl(audio_fd, SNDCTL_DSP_SETFMT, &value) < 0) ||
 						(value != format) ) {
 		SDL_SetError("Couldn't set audio format");
 		return(-1);
 	}

 	/* Set mono or stereo audio (currently only two channels supported) */
 	stereo = (spec->channels > 1);
 	ioctl(audio_fd, SNDCTL_DSP_STEREO, &stereo);
 	if ( stereo ) {
 		spec->channels = 2;
 	} else {
 		spec->channels = 1;
 	}

 	/* Because some drivers don't allow setting the buffer size
 	   after setting the format, we must re-open the audio device
 	   once we know what format and channels are supported
 	 */
 	if ( DMA_ReopenAudio(this, audiodev, format, stereo, spec) < 0 ) {
 		/* Error is set by DMA_ReopenAudio() */
 		return(-1);
 	}

 	/* Memory map the audio buffer */
 	if ( ioctl(audio_fd, SNDCTL_DSP_GETOSPACE, &info) < 0 ) {
 		SDL_SetError("Couldn't get OSPACE parameters");
 		return(-1);
 	}
 	spec->size = info.fragsize;
 	spec->samples = spec->size / ((spec->format & 0xFF) / 8);
 	spec->samples /= spec->channels;
 	num_buffers = info.fragstotal;
 	dma_len = num_buffers*spec->size;
 	dma_buf = (Uint8 *)mmap(NULL, dma_len, PROT_WRITE, MAP_SHARED,
 							audio_fd, 0);
 	if ( dma_buf == MAP_FAILED ) {
 		SDL_SetError("DMA memory map failed");
 		dma_buf = NULL;
 		return(-1);
 	}
 	SDL_memset(dma_buf, spec->silence, dma_len);

 	/* Check to see if we need to use select() workaround */
 	{ char *workaround;
 		workaround = SDL_getenv("SDL_DSP_NOSELECT");
 		if ( workaround ) {
 			frame_ticks = (float)(spec->samples*1000)/spec->freq;
 			next_frame = SDL_GetTicks()+frame_ticks;
 		}
 	}

 	/* Trigger audio playback */
 	value = 0;
 	ioctl(audio_fd, SNDCTL_DSP_SETTRIGGER, &value);
 	value = PCM_ENABLE_OUTPUT;
 	if ( ioctl(audio_fd, SNDCTL_DSP_SETTRIGGER, &value) < 0 ) {
 		SDL_SetError("Couldn't trigger audio output");
 		return(-1);
 	}

 	/* Get the parent process id (we're the parent of the audio thread) */
 	parent = getpid();

 	/* We're ready to rock and roll. :-) */
 	return(0);
 }
	/*
	SDL - Simple DirectMedia Layer
	Copyright (C) 1997-2009 Sam Lantinga

	This library is free software; you can redistribute it and/or
	modify it under the terms of the GNU Lesser General Public
	License as published by the Free Software Foundation; either
	version 2.1 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
	Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public
	License along with this library; if not, write to the Free Software
	Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

	Sam Lantinga
	slouken@libsdl.org
	*/
	#include "SDL_config.h"

	/* Allow access to a raw mixing buffer */

	#include <stdio.h>
	#include <string.h> /* For strerror() */
	#include <errno.h>
	#include <unistd.h>
	#include <fcntl.h>
	#include <signal.h>
	#include <sys/types.h>
	#include <sys/time.h>
	#include <sys/ioctl.h>
	#include <sys/stat.h>
	#include <sys/mman.h>

	#if SDL_AUDIO_DRIVER_OSS_SOUNDCARD_H
	/* This is installed on some systems */
	#include <soundcard.h>
	#else
	/* This is recommended by OSS */
	#include <sys/soundcard.h>
	#endif

	#ifndef MAP_FAILED
	#define MAP_FAILED ((Uint8 *)-1)
	#endif

	#include "SDL_timer.h"
	#include "SDL_audio.h"
	#include "../SDL_audio_c.h"
	#include "../SDL_audiodev_c.h"
	#include "SDL_dmaaudio.h"

	/* The tag name used by DMA audio */
	#define DMA_DRIVER_NAME "dma"

	/* Open the audio device for playback, and don't block if busy */
	#define OPEN_FLAGS (O_RDWR\|O_NONBLOCK)

	/* Audio driver functions */
	static int DMA_OpenAudio(_THIS, SDL_AudioSpec *spec);
	static void DMA_WaitAudio(_THIS);
	static void DMA_PlayAudio(_THIS);
	static Uint8 *DMA_GetAudioBuf(_THIS);
	static void DMA_CloseAudio(_THIS);

	/* Audio driver bootstrap functions */

	static int Audio_Available(void)
	{
	int available;
	int fd;

	available = 0;

	fd = SDL_OpenAudioPath(NULL, 0, OPEN_FLAGS, 0);
	if ( fd >= 0 ) {
	int caps;
	struct audio_buf_info info;

	if ( (ioctl(fd, SNDCTL_DSP_GETCAPS, &caps) == 0) &&
	(caps & DSP_CAP_TRIGGER) && (caps & DSP_CAP_MMAP) &&
	(ioctl(fd, SNDCTL_DSP_GETOSPACE, &info) == 0) ) {
	available = 1;
	}
	close(fd);
	}
	return(available);
	}

	static void Audio_DeleteDevice(SDL_AudioDevice *device)
	{
	SDL_free(device->hidden);
	SDL_free(device);
	}

	static SDL_AudioDevice *Audio_CreateDevice(int devindex)
	{
	SDL_AudioDevice *this;

	/* Initialize all variables that we clean on shutdown */
	this = (SDL_AudioDevice *)SDL_malloc(sizeof(SDL_AudioDevice));
	if ( this ) {
	SDL_memset(this, 0, (sizeof *this));
	this->hidden = (struct SDL_PrivateAudioData *)
	SDL_malloc((sizeof *this->hidden));
	}
	if ( (this == NULL) \|\| (this->hidden == NULL) ) {
	SDL_OutOfMemory();
	if ( this ) {
	SDL_free(this);
	}
	return(0);
	}
	SDL_memset(this->hidden, 0, (sizeof *this->hidden));
	audio_fd = -1;

	/* Set the function pointers */
	this->OpenAudio = DMA_OpenAudio;
	this->WaitAudio = DMA_WaitAudio;
	this->PlayAudio = DMA_PlayAudio;
	this->GetAudioBuf = DMA_GetAudioBuf;
	this->CloseAudio = DMA_CloseAudio;

	this->free = Audio_DeleteDevice;

	return this;
	}

	AudioBootStrap DMA_bootstrap = {
	DMA_DRIVER_NAME, "OSS /dev/dsp DMA audio",
	Audio_Available, Audio_CreateDevice
	};

	/* This function waits until it is possible to write a full sound buffer */
	static void DMA_WaitAudio(_THIS)
	{
	fd_set fdset;

	/* Check to see if the thread-parent process is still alive */
	{ static int cnt = 0;
	/* Note that this only works with thread implementations
	that use a different process id for each thread.
	*/
	if (parent && (((++cnt)%10) == 0)) { /* Check every 10 loops */
	if ( kill(parent, 0) < 0 ) {
	this->enabled = 0;
	}
	}
	}

	/* See if we need to use timed audio synchronization */
	if ( frame_ticks ) {
	/* Use timer for general audio synchronization */
	Sint32 ticks;

	ticks = ((Sint32)(next_frame - SDL_GetTicks()))-FUDGE_TICKS;
	if ( ticks > 0 ) {
	SDL_Delay(ticks);
	}
	} else {
	/* Use select() for audio synchronization */
	struct timeval timeout;
	FD_ZERO(&fdset);
	FD_SET(audio_fd, &fdset);
	timeout.tv_sec = 10;
	timeout.tv_usec = 0;
	#ifdef DEBUG_AUDIO
	fprintf(stderr, "Waiting for audio to get ready\n");
	#endif
	if ( select(audio_fd+1, NULL, &fdset, NULL, &timeout) <= 0 ) {
	const char *message =
	#ifdef AUDIO_OSPACE_HACK
	"Audio timeout - buggy audio driver? (trying ospace)";
	#else
	"Audio timeout - buggy audio driver? (disabled)";
	#endif
	/* In general we should never print to the screen,
	but in this case we have no other way of letting
	the user know what happened.
	*/
	fprintf(stderr, "SDL: %s\n", message);
	#ifdef AUDIO_OSPACE_HACK
	/* We may be able to use GET_OSPACE trick */
	frame_ticks = (float)(this->spec->samples*1000) /
	this->spec->freq;
	next_frame = SDL_GetTicks()+frame_ticks;
	#else
	this->enabled = 0;
	/* Don't try to close - may hang */
	audio_fd = -1;
	#ifdef DEBUG_AUDIO
	fprintf(stderr, "Done disabling audio\n");
	#endif
	#endif /* AUDIO_OSPACE_HACK */
	}
	#ifdef DEBUG_AUDIO
	fprintf(stderr, "Ready!\n");
	#endif
	}
	}

	static void DMA_PlayAudio(_THIS)
	{
	/* If timer synchronization is enabled, set the next write frame */
	if ( frame_ticks ) {
	next_frame += frame_ticks;
	}
	return;
	}

	static Uint8 *DMA_GetAudioBuf(_THIS)
	{
	count_info info;
	int playing;
	int filling;

	/* Get number of blocks, looping if we're not using select() */
	do {
	if ( ioctl(audio_fd, SNDCTL_DSP_GETOPTR, &info) < 0 ) {
	/* Uh oh... */
	this->enabled = 0;
	return(NULL);
	}
	} while ( frame_ticks && (info.blocks < 1) );
	#ifdef DEBUG_AUDIO
	if ( info.blocks > 1 ) {
	printf("Warning: audio underflow (%d frags)\n", info.blocks-1);
	}
	#endif
	playing = info.ptr / this->spec.size;
	filling = (playing + 1)%num_buffers;
	return (dma_buf + (filling * this->spec.size));
	}

	static void DMA_CloseAudio(_THIS)
	{
	if ( dma_buf != NULL ) {
	munmap(dma_buf, dma_len);
	dma_buf = NULL;
	}
	if ( audio_fd >= 0 ) {
	close(audio_fd);
	audio_fd = -1;
	}
	}

	static int DMA_ReopenAudio(_THIS, const char *audiodev, int format, int stereo,
	SDL_AudioSpec *spec)
	{
	int frag_spec;
	int value;

	/* Close and then reopen the audio device */
	close(audio_fd);
	audio_fd = open(audiodev, O_RDWR, 0);
	if ( audio_fd < 0 ) {
	SDL_SetError("Couldn't open %s: %s", audiodev, strerror(errno));
	return(-1);
	}

	/* Calculate the final parameters for this audio specification */
	SDL_CalculateAudioSpec(spec);

	/* Determine the power of two of the fragment size */
	for ( frag_spec = 0; (0x01<<frag_spec) < spec->size; ++frag_spec );
	if ( (0x01<<frag_spec) != spec->size ) {
	SDL_SetError("Fragment size must be a power of two");
	return(-1);
	}

	/* Set the audio buffering parameters */
	if ( ioctl(audio_fd, SNDCTL_DSP_SETFRAGMENT, &frag_spec) < 0 ) {
	SDL_SetError("Couldn't set audio fragment spec");
	return(-1);
	}

	/* Set the audio format */
	value = format;
	if ( (ioctl(audio_fd, SNDCTL_DSP_SETFMT, &value) < 0) \|\|
	(value != format) ) {
	SDL_SetError("Couldn't set audio format");
	return(-1);
	}

	/* Set mono or stereo audio */
	value = (spec->channels > 1);
	if ( (ioctl(audio_fd, SNDCTL_DSP_STEREO, &stereo) < 0) \|\|
	(value != stereo) ) {
	SDL_SetError("Couldn't set audio channels");
	return(-1);
	}

	/* Set the DSP frequency */
	value = spec->freq;
	if ( ioctl(audio_fd, SNDCTL_DSP_SPEED, &value) < 0 ) {
	SDL_SetError("Couldn't set audio frequency");
	return(-1);
	}
	spec->freq = value;

	/* We successfully re-opened the audio */
	return(0);
	}

	static int DMA_OpenAudio(_THIS, SDL_AudioSpec *spec)
	{
	char audiodev[1024];
	int format;
	int stereo;
	int value;
	Uint16 test_format;
	struct audio_buf_info info;

	/* Reset the timer synchronization flag */
	frame_ticks = 0.0;

	/* Open the audio device */
	audio_fd = SDL_OpenAudioPath(audiodev, sizeof(audiodev), OPEN_FLAGS, 0);
	if ( audio_fd < 0 ) {
	SDL_SetError("Couldn't open %s: %s", audiodev, strerror(errno));
	return(-1);
	}
	dma_buf = NULL;
	ioctl(audio_fd, SNDCTL_DSP_RESET, 0);

	/* Get a list of supported hardware formats */
	if ( ioctl(audio_fd, SNDCTL_DSP_GETFMTS, &value) < 0 ) {
	SDL_SetError("Couldn't get audio format list");
	return(-1);
	}

	/* Try for a closest match on audio format */
	format = 0;
	for ( test_format = SDL_FirstAudioFormat(spec->format);
	! format && test_format; ) {
	#ifdef DEBUG_AUDIO
	fprintf(stderr, "Trying format 0x%4.4x\n", test_format);
	#endif
	switch ( test_format ) {
	case AUDIO_U8:
	if ( value & AFMT_U8 ) {
	format = AFMT_U8;
	}
	break;
	case AUDIO_S8:
	if ( value & AFMT_S8 ) {
	format = AFMT_S8;
	}
	break;
	case AUDIO_S16LSB:
	if ( value & AFMT_S16_LE ) {
	format = AFMT_S16_LE;
	}
	break;
	case AUDIO_S16MSB:
	if ( value & AFMT_S16_BE ) {
	format = AFMT_S16_BE;
	}
	break;
	case AUDIO_U16LSB:
	if ( value & AFMT_U16_LE ) {
	format = AFMT_U16_LE;
	}
	break;
	case AUDIO_U16MSB:
	if ( value & AFMT_U16_BE ) {
	format = AFMT_U16_BE;
	}
	break;
	default:
	format = 0;
	break;
	}
	if ( ! format ) {
	test_format = SDL_NextAudioFormat();
	}
	}
	if ( format == 0 ) {
	SDL_SetError("Couldn't find any hardware audio formats");
	return(-1);
	}
	spec->format = test_format;

	/* Set the audio format */
	value = format;
	if ( (ioctl(audio_fd, SNDCTL_DSP_SETFMT, &value) < 0) \|\|
	(value != format) ) {
	SDL_SetError("Couldn't set audio format");
	return(-1);
	}

	/* Set mono or stereo audio (currently only two channels supported) */
	stereo = (spec->channels > 1);
	ioctl(audio_fd, SNDCTL_DSP_STEREO, &stereo);
	if ( stereo ) {
	spec->channels = 2;
	} else {
	spec->channels = 1;
	}

	/* Because some drivers don't allow setting the buffer size
	after setting the format, we must re-open the audio device
	once we know what format and channels are supported
	*/
	if ( DMA_ReopenAudio(this, audiodev, format, stereo, spec) < 0 ) {
	/* Error is set by DMA_ReopenAudio() */
	return(-1);
	}

	/* Memory map the audio buffer */
	if ( ioctl(audio_fd, SNDCTL_DSP_GETOSPACE, &info) < 0 ) {
	SDL_SetError("Couldn't get OSPACE parameters");
	return(-1);
	}
	spec->size = info.fragsize;
	spec->samples = spec->size / ((spec->format & 0xFF) / 8);
	spec->samples /= spec->channels;
	num_buffers = info.fragstotal;
	dma_len = num_buffers*spec->size;
	dma_buf = (Uint8 *)mmap(NULL, dma_len, PROT_WRITE, MAP_SHARED,
	audio_fd, 0);
	if ( dma_buf == MAP_FAILED ) {
	SDL_SetError("DMA memory map failed");
	dma_buf = NULL;
	return(-1);
	}
	SDL_memset(dma_buf, spec->silence, dma_len);

	/* Check to see if we need to use select() workaround */
	{ char *workaround;
	workaround = SDL_getenv("SDL_DSP_NOSELECT");
	if ( workaround ) {
	frame_ticks = (float)(spec->samples*1000)/spec->freq;
	next_frame = SDL_GetTicks()+frame_ticks;
	}
	}

	/* Trigger audio playback */
	value = 0;
	ioctl(audio_fd, SNDCTL_DSP_SETTRIGGER, &value);
	value = PCM_ENABLE_OUTPUT;
	if ( ioctl(audio_fd, SNDCTL_DSP_SETTRIGGER, &value) < 0 ) {
	SDL_SetError("Couldn't trigger audio output");
	return(-1);
	}

	/* Get the parent process id (we're the parent of the audio thread) */
	parent = getpid();

	/* We're ready to rock and roll. :-) */
	return(0);
	}