src/audio/dsp/SDL_dspaudio.c

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2006 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

    Modified in Oct 2004 by Hannu Savolainen 
    hannu@opensound.com
*/
#include "SDL_config.h"

/* Allow access to a raw mixing buffer */

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

#include "SDL_timer.h"
#include "SDL_audio.h"
#include "../SDL_audiomem.h"
#include "../SDL_audio_c.h"
#include "../SDL_audiodev_c.h"
#include "SDL_dspaudio.h"

/* The tag name used by DSP audio */
#define DSP_DRIVER_NAME         "dsp"

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

/* Audio driver functions */
static int DSP_OpenAudio (_THIS, SDL_AudioSpec * spec);
static void DSP_WaitAudio (_THIS);
static void DSP_PlayAudio (_THIS);
static Uint8 *DSP_GetAudioBuf (_THIS);
static void DSP_CloseAudio (_THIS);

/* Audio driver bootstrap functions */

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

    available = 0;
    fd = SDL_OpenAudioPath (NULL, 0, OPEN_FLAGS, 0);
    if (fd >= 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 = DSP_OpenAudio;
    this->WaitAudio = DSP_WaitAudio;
    this->PlayAudio = DSP_PlayAudio;
    this->GetAudioBuf = DSP_GetAudioBuf;
    this->CloseAudio = DSP_CloseAudio;

    this->free = Audio_DeleteDevice;

    return this;
}

AudioBootStrap DSP_bootstrap = {
    DSP_DRIVER_NAME, "OSS /dev/dsp standard audio",
    Audio_Available, Audio_CreateDevice
};

/* This function waits until it is possible to write a full sound buffer */
static void
DSP_WaitAudio (_THIS)
{
    /* Not needed at all since OSS handles waiting automagically */
}

static void
DSP_PlayAudio (_THIS)
{
    if (write (audio_fd, mixbuf, mixlen) == -1) {
        perror ("Audio write");
        this->enabled = 0;
    }
#ifdef DEBUG_AUDIO
    fprintf (stderr, "Wrote %d bytes of audio data\n", mixlen);
#endif
}

static Uint8 *
DSP_GetAudioBuf (_THIS)
{
    return (mixbuf);
}

static void
DSP_CloseAudio (_THIS)
{
    if (mixbuf != NULL) {
        SDL_FreeAudioMem (mixbuf);
        mixbuf = NULL;
    }
    if (audio_fd >= 0) {
        close (audio_fd);
        audio_fd = -1;
    }
}

static int
DSP_OpenAudio (_THIS, SDL_AudioSpec * spec)
{
    char audiodev[1024];
    int format;
    int value;
    int frag_spec;
    Uint16 test_format;

    /* 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);
    }
    mixbuf = NULL;

    /* Make the file descriptor use blocking writes with fcntl() */
    {
        long flags;
        flags = fcntl (audio_fd, F_GETFL);
        flags &= ~O_NONBLOCK;
        if (fcntl (audio_fd, F_SETFL, flags) < 0) {
            SDL_SetError ("Couldn't set audio blocking mode");
            DSP_CloseAudio (this);
            return (-1);
        }
    }

    /* Get a list of supported hardware formats */
    if (ioctl (audio_fd, SNDCTL_DSP_GETFMTS, &value) < 0) {
        perror ("SNDCTL_DSP_GETFMTS");
        SDL_SetError ("Couldn't get audio format list");
        DSP_CloseAudio (this);
        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_S16LSB:
            if (value & AFMT_S16_LE) {
                format = AFMT_S16_LE;
            }
            break;
        case AUDIO_S16MSB:
            if (value & AFMT_S16_BE) {
                format = AFMT_S16_BE;
            }
            break;
#if 0
/*
 * These formats are not used by any real life systems so they are not 
 * needed here.
 */
        case AUDIO_S8:
            if (value & AFMT_S8) {
                format = AFMT_S8;
            }
            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;
#endif
        default:
            format = 0;
            break;
        }
        if (!format) {
            test_format = SDL_NextAudioFormat ();
        }
    }
    if (format == 0) {
        SDL_SetError ("Couldn't find any hardware audio formats");
        DSP_CloseAudio (this);
        return (-1);
    }
    spec->format = test_format;

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

    /* Set the number of channels of output */
    value = spec->channels;
    if (ioctl (audio_fd, SNDCTL_DSP_CHANNELS, &value) < 0) {
        perror ("SNDCTL_DSP_CHANNELS");
        SDL_SetError ("Cannot set the number of channels");
        DSP_CloseAudio (this);
        return (-1);
    }
    spec->channels = value;

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

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

    /* Determine the power of two of the fragment size */
    for (frag_spec = 0; (0x01U << frag_spec) < spec->size; ++frag_spec);
    if ((0x01U << frag_spec) != spec->size) {
        SDL_SetError ("Fragment size must be a power of two");
        DSP_CloseAudio (this);
        return (-1);
    }
    frag_spec |= 0x00020000;    /* two fragments, for low latency */

    /* Set the audio buffering parameters */
#ifdef DEBUG_AUDIO
    fprintf (stderr, "Requesting %d fragments of size %d\n",
             (frag_spec >> 16), 1 << (frag_spec & 0xFFFF));
#endif
    if (ioctl (audio_fd, SNDCTL_DSP_SETFRAGMENT, &frag_spec) < 0) {
        perror ("SNDCTL_DSP_SETFRAGMENT");
    }
#ifdef DEBUG_AUDIO
    {
        audio_buf_info info;
        ioctl (audio_fd, SNDCTL_DSP_GETOSPACE, &info);
        fprintf (stderr, "fragments = %d\n", info.fragments);
        fprintf (stderr, "fragstotal = %d\n", info.fragstotal);
        fprintf (stderr, "fragsize = %d\n", info.fragsize);
        fprintf (stderr, "bytes = %d\n", info.bytes);
    }
#endif

    /* Allocate mixing buffer */
    mixlen = spec->size;
    mixbuf = (Uint8 *) SDL_AllocAudioMem (mixlen);
    if (mixbuf == NULL) {
        DSP_CloseAudio (this);
        return (-1);
    }
    SDL_memset (mixbuf, spec->silence, spec->size);

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

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

/* vi: set ts=4 sw=4 expandtab: */