src/audio/alsa/SDL_alsa_audio.c

   1 /*
   2     SDL - Simple DirectMedia Layer
   3     Copyright (C) 1997-2009 Sam Lantinga
   4
   5     This library is free software; you can redistribute it and/or
   6     modify it under the terms of the GNU Library General Public
   7     License as published by the Free Software Foundation; either
   8     version 2 of the License, or (at your option) any later version.
   9
  10     This library is distributed in the hope that it will be useful,
  11     but WITHOUT ANY WARRANTY; without even the implied warranty of
  12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13     Library General Public License for more details.
  14
  15     You should have received a copy of the GNU Library General Public
  16     License along with this library; if not, write to the Free
  17     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18
  19     Sam Lantinga
  20     slouken@libsdl.org
  21 */
  22 #include "SDL_config.h"
  23
  24 /* Allow access to a raw mixing buffer */
  25
  26 #include <sys/types.h>
  27 #include <signal.h>     /* For kill() */
  28
  29 #include "SDL_timer.h"
  30 #include "SDL_audio.h"
  31 #include "../SDL_audiomem.h"
  32 #include "../SDL_audio_c.h"
  33 #include "SDL_alsa_audio.h"
  34
  35 #ifdef SDL_AUDIO_DRIVER_ALSA_DYNAMIC
  36 #include "SDL_name.h"
  37 #include "SDL_loadso.h"
  38 #else
  39 #define SDL_NAME(X)     X
  40 #endif
  41
  42
  43 /* The tag name used by ALSA audio */
  44 #define DRIVER_NAME         "alsa"
  45
  46 /* Audio driver functions */
  47 static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec);
  48 static void ALSA_WaitAudio(_THIS);
  49 static void ALSA_PlayAudio(_THIS);
  50 static Uint8 *ALSA_GetAudioBuf(_THIS);
  51 static void ALSA_CloseAudio(_THIS);
  52
  53 #ifdef SDL_AUDIO_DRIVER_ALSA_DYNAMIC
  54
  55 static const char *alsa_library = SDL_AUDIO_DRIVER_ALSA_DYNAMIC;
  56 static void *alsa_handle = NULL;
  57 static int alsa_loaded = 0;
  58
  59 static int (*SDL_NAME(snd_pcm_open))(snd_pcm_t **pcm, const char *name, snd_pcm_stream_t stream, int mode);
  60 static int (*SDL_NAME(snd_pcm_close))(snd_pcm_t *pcm);
  61 static snd_pcm_sframes_t (*SDL_NAME(snd_pcm_writei))(snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size);
  62 static int (*SDL_NAME(snd_pcm_recover))(snd_pcm_t *pcm, int err, int silent);
  63 static int (*SDL_NAME(snd_pcm_prepare))(snd_pcm_t *pcm);
  64 static int (*SDL_NAME(snd_pcm_drain))(snd_pcm_t *pcm);
  65 static const char *(*SDL_NAME(snd_strerror))(int errnum);
  66 static size_t (*SDL_NAME(snd_pcm_hw_params_sizeof))(void);
  67 static size_t (*SDL_NAME(snd_pcm_sw_params_sizeof))(void);
  68 static void (*SDL_NAME(snd_pcm_hw_params_copy))(snd_pcm_hw_params_t *dst, const snd_pcm_hw_params_t *src);
  69 static int (*SDL_NAME(snd_pcm_hw_params_any))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params);
  70 static int (*SDL_NAME(snd_pcm_hw_params_set_access))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, snd_pcm_access_t access);
  71 static int (*SDL_NAME(snd_pcm_hw_params_set_format))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, snd_pcm_format_t val);
  72 static int (*SDL_NAME(snd_pcm_hw_params_set_channels))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, unsigned int val);
  73 static int (*SDL_NAME(snd_pcm_hw_params_get_channels))(const snd_pcm_hw_params_t *params, unsigned int *val);
  74 static int (*SDL_NAME(snd_pcm_hw_params_set_rate_near))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, unsigned int *val, int *dir);
  75 static int (*SDL_NAME(snd_pcm_hw_params_set_period_size_near))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val, int *dir);
  76 static int (*SDL_NAME(snd_pcm_hw_params_get_period_size))(const snd_pcm_hw_params_t *params, snd_pcm_uframes_t *frames, int *dir);
  77 static int (*SDL_NAME(snd_pcm_hw_params_set_periods_near))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, unsigned int *val, int *dir);
  78 static int (*SDL_NAME(snd_pcm_hw_params_get_periods))(const snd_pcm_hw_params_t *params, unsigned int *val, int *dir);
  79 static int (*SDL_NAME(snd_pcm_hw_params_set_buffer_size_near))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val);
  80 static int (*SDL_NAME(snd_pcm_hw_params_get_buffer_size))(const snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val);
  81 static int (*SDL_NAME(snd_pcm_hw_params))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params);
  82 /*
  83 */
  84 static int (*SDL_NAME(snd_pcm_sw_params_current))(snd_pcm_t *pcm, snd_pcm_sw_params_t *swparams);
  85 static int (*SDL_NAME(snd_pcm_sw_params_set_start_threshold))(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val);
  86 static int (*SDL_NAME(snd_pcm_sw_params))(snd_pcm_t *pcm, snd_pcm_sw_params_t *params);
  87 static int (*SDL_NAME(snd_pcm_nonblock))(snd_pcm_t *pcm, int nonblock);
  88 static int (*SDL_NAME(snd_pcm_wait))(snd_pcm_t *pcm, int timeout);
  89 #define snd_pcm_hw_params_sizeof SDL_NAME(snd_pcm_hw_params_sizeof)
  90 #define snd_pcm_sw_params_sizeof SDL_NAME(snd_pcm_sw_params_sizeof)
  91
  92 /* cast funcs to char* first, to please GCC's strict aliasing rules. */
  93 static struct {
  94         const char *name;
  95         void **func;
  96 } alsa_functions[] = {
  97         { "snd_pcm_open",       (void**)(char*)&SDL_NAME(snd_pcm_open)          },
  98         { "snd_pcm_close",      (void**)(char*)&SDL_NAME(snd_pcm_close) },
  99         { "snd_pcm_writei",     (void**)(char*)&SDL_NAME(snd_pcm_writei)        },
 100         { "snd_pcm_recover",    (void**)(char*)&SDL_NAME(snd_pcm_recover)       },
 101         { "snd_pcm_prepare",    (void**)(char*)&SDL_NAME(snd_pcm_prepare)       },
 102         { "snd_pcm_drain",      (void**)(char*)&SDL_NAME(snd_pcm_drain) },
 103         { "snd_strerror",       (void**)(char*)&SDL_NAME(snd_strerror)          },
 104         { "snd_pcm_hw_params_sizeof",           (void**)(char*)&SDL_NAME(snd_pcm_hw_params_sizeof)              },
 105         { "snd_pcm_sw_params_sizeof",           (void**)(char*)&SDL_NAME(snd_pcm_sw_params_sizeof)              },
 106         { "snd_pcm_hw_params_copy",             (void**)(char*)&SDL_NAME(snd_pcm_hw_params_copy)                },
 107         { "snd_pcm_hw_params_any",              (void**)(char*)&SDL_NAME(snd_pcm_hw_params_any)         },
 108         { "snd_pcm_hw_params_set_access",       (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_access)          },
 109         { "snd_pcm_hw_params_set_format",       (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_format)          },
 110         { "snd_pcm_hw_params_set_channels",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_channels)        },
 111         { "snd_pcm_hw_params_get_channels",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_channels)        },
 112         { "snd_pcm_hw_params_set_rate_near",    (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_rate_near)       },
 113         { "snd_pcm_hw_params_set_period_size_near",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_period_size_near)        },
 114         { "snd_pcm_hw_params_get_period_size",  (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_period_size)     },
 115         { "snd_pcm_hw_params_set_periods_near", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_periods_near)    },
 116         { "snd_pcm_hw_params_get_periods",      (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_periods) },
 117         { "snd_pcm_hw_params_set_buffer_size_near",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_buffer_size_near) },
 118         { "snd_pcm_hw_params_get_buffer_size",  (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_buffer_size) },
 119         { "snd_pcm_hw_params",  (void**)(char*)&SDL_NAME(snd_pcm_hw_params)     },
 120         { "snd_pcm_sw_params_current",  (void**)(char*)&SDL_NAME(snd_pcm_sw_params_current)     },
 121         { "snd_pcm_sw_params_set_start_threshold",      (void**)(char*)&SDL_NAME(snd_pcm_sw_params_set_start_threshold) },
 122         { "snd_pcm_sw_params",  (void**)(char*)&SDL_NAME(snd_pcm_sw_params)     },
 123         { "snd_pcm_nonblock",   (void**)(char*)&SDL_NAME(snd_pcm_nonblock)      },
 124         { "snd_pcm_wait",       (void**)(char*)&SDL_NAME(snd_pcm_wait)  },
 125 };
 126
 127 static void UnloadALSALibrary(void) {
 128         if (alsa_loaded) {
 129                 SDL_UnloadObject(alsa_handle);
 130                 alsa_handle = NULL;
 131                 alsa_loaded = 0;
 132         }
 133 }
 134
 135 static int LoadALSALibrary(void) {
 136         int i, retval = -1;
 137
 138         alsa_handle = SDL_LoadObject(alsa_library);
 139         if (alsa_handle) {
 140                 alsa_loaded = 1;
 141                 retval = 0;
 142                 for (i = 0; i < SDL_arraysize(alsa_functions); i++) {
 143                         *alsa_functions[i].func = SDL_LoadFunction(alsa_handle,alsa_functions[i].name);
 144                         if (!*alsa_functions[i].func) {
 145                                 retval = -1;
 146                                 UnloadALSALibrary();
 147                                 break;
 148                         }
 149                 }
 150         }
 151         return retval;
 152 }
 153
 154 #else
 155
 156 static void UnloadALSALibrary(void) {
 157         return;
 158 }
 159
 160 static int LoadALSALibrary(void) {
 161         return 0;
 162 }
 163
 164 #endif /* SDL_AUDIO_DRIVER_ALSA_DYNAMIC */
 165
 166 static const char *get_audio_device(int channels)
 167 {
 168         const char *device;
 169
 170         device = SDL_getenv("AUDIODEV");        /* Is there a standard variable name? */
 171         if ( device == NULL ) {
 172                 switch (channels) {
 173                 case 6:
 174                         device = "plug:surround51";
 175                         break;
 176                 case 4:
 177                         device = "plug:surround40";
 178                         break;
 179                 default:
 180                         device = "default";
 181                         break;
 182                 }
 183         }
 184         return device;
 185 }
 186
 187 /* Audio driver bootstrap functions */
 188
 189 static int Audio_Available(void)
 190 {
 191         int available;
 192         int status;
 193         snd_pcm_t *handle;
 194
 195         available = 0;
 196         if (LoadALSALibrary() < 0) {
 197                 return available;
 198         }
 199         status = SDL_NAME(snd_pcm_open)(&handle, get_audio_device(2), SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
 200         if ( status >= 0 ) {
 201                 available = 1;
 202                 SDL_NAME(snd_pcm_close)(handle);
 203         }
 204         UnloadALSALibrary();
 205         return(available);
 206 }
 207
 208 static void Audio_DeleteDevice(SDL_AudioDevice *device)
 209 {
 210         SDL_free(device->hidden);
 211         SDL_free(device);
 212         UnloadALSALibrary();
 213 }
 214
 215 static SDL_AudioDevice *Audio_CreateDevice(int devindex)
 216 {
 217         SDL_AudioDevice *this;
 218
 219         /* Initialize all variables that we clean on shutdown */
 220         LoadALSALibrary();
 221         this = (SDL_AudioDevice *)SDL_malloc(sizeof(SDL_AudioDevice));
 222         if ( this ) {
 223                 SDL_memset(this, 0, (sizeof *this));
 224                 this->hidden = (struct SDL_PrivateAudioData *)
 225                                 SDL_malloc((sizeof *this->hidden));
 226         }
 227         if ( (this == NULL) || (this->hidden == NULL) ) {
 228                 SDL_OutOfMemory();
 229                 if ( this ) {
 230                         SDL_free(this);
 231                 }
 232                 return(0);
 233         }
 234         SDL_memset(this->hidden, 0, (sizeof *this->hidden));
 235
 236         /* Set the function pointers */
 237         this->OpenAudio = ALSA_OpenAudio;
 238         this->WaitAudio = ALSA_WaitAudio;
 239         this->PlayAudio = ALSA_PlayAudio;
 240         this->GetAudioBuf = ALSA_GetAudioBuf;
 241         this->CloseAudio = ALSA_CloseAudio;
 242
 243         this->free = Audio_DeleteDevice;
 244
 245         return this;
 246 }
 247
 248 AudioBootStrap ALSA_bootstrap = {
 249         DRIVER_NAME, "ALSA PCM audio",
 250         Audio_Available, Audio_CreateDevice
 251 };
 252
 253 /* This function waits until it is possible to write a full sound buffer */
 254 static void ALSA_WaitAudio(_THIS)
 255 {
 256         /* We're in blocking mode, so there's nothing to do here */
 257 }
 258
 259
 260 /*
 261  * http://bugzilla.libsdl.org/show_bug.cgi?id=110
 262  * "For Linux ALSA, this is FL-FR-RL-RR-C-LFE
 263  *  and for Windows DirectX [and CoreAudio], this is FL-FR-C-LFE-RL-RR"
 264  */
 265 #define SWIZ6(T) \
 266     T *ptr = (T *) mixbuf; \
 267     const Uint32 count = (this->spec.samples / 6); \
 268     Uint32 i; \
 269     for (i = 0; i < count; i++, ptr += 6) { \
 270         T tmp; \
 271         tmp = ptr[2]; ptr[2] = ptr[4]; ptr[4] = tmp; \
 272         tmp = ptr[3]; ptr[3] = ptr[5]; ptr[5] = tmp; \
 273     }
 274
 275 static __inline__ void swizzle_alsa_channels_6_64bit(_THIS) { SWIZ6(Uint64); }
 276 static __inline__ void swizzle_alsa_channels_6_32bit(_THIS) { SWIZ6(Uint32); }
 277 static __inline__ void swizzle_alsa_channels_6_16bit(_THIS) { SWIZ6(Uint16); }
 278 static __inline__ void swizzle_alsa_channels_6_8bit(_THIS) { SWIZ6(Uint8); }
 279
 280 #undef SWIZ6
 281
 282
 283 /*
 284  * Called right before feeding this->mixbuf to the hardware. Swizzle channels
 285  *  from Windows/Mac order to the format alsalib will want.
 286  */
 287 static __inline__ void swizzle_alsa_channels(_THIS)
 288 {
 289     if (this->spec.channels == 6) {
 290         const Uint16 fmtsize = (this->spec.format & 0xFF); /* bits/channel. */
 291         if (fmtsize == 16)
 292             swizzle_alsa_channels_6_16bit(this);
 293         else if (fmtsize == 8)
 294             swizzle_alsa_channels_6_8bit(this);
 295         else if (fmtsize == 32)
 296             swizzle_alsa_channels_6_32bit(this);
 297         else if (fmtsize == 64)
 298             swizzle_alsa_channels_6_64bit(this);
 299     }
 300
 301     /* !!! FIXME: update this for 7.1 if needed, later. */
 302 }
 303
 304
 305 static void ALSA_PlayAudio(_THIS)
 306 {
 307         int status;
 308         snd_pcm_uframes_t frames_left;
 309         const Uint8 *sample_buf = (const Uint8 *) mixbuf;
 310         const int frame_size = (((int) (this->spec.format & 0xFF)) / 8) * this->spec.channels;
 311
 312         swizzle_alsa_channels(this);
 313
 314         frames_left = ((snd_pcm_uframes_t) this->spec.samples);
 315
 316         while ( frames_left > 0 && this->enabled ) {
 317                 /* This works, but needs more testing before going live */
 318                 /*SDL_NAME(snd_pcm_wait)(pcm_handle, -1);*/
 319
 320                 status = SDL_NAME(snd_pcm_writei)(pcm_handle, sample_buf, frames_left);
 321                 if ( status < 0 ) {
 322                         if ( status == -EAGAIN ) {
 323                                 /* Apparently snd_pcm_recover() doesn't handle this case - does it assume snd_pcm_wait() above? */
 324                                 SDL_Delay(1);
 325                                 continue;
 326                         }
 327                         status = SDL_NAME(snd_pcm_recover)(pcm_handle, status, 0);
 328                         if ( status < 0 ) {
 329                                 /* Hmm, not much we can do - abort */
 330                                 fprintf(stderr, "ALSA write failed (unrecoverable): %s\n", SDL_NAME(snd_strerror)(status));
 331                                 this->enabled = 0;
 332                                 return;
 333                         }
 334                         continue;
 335                 }
 336                 sample_buf += status * frame_size;
 337                 frames_left -= status;
 338         }
 339 }
 340
 341 static Uint8 *ALSA_GetAudioBuf(_THIS)
 342 {
 343         return(mixbuf);
 344 }
 345
 346 static void ALSA_CloseAudio(_THIS)
 347 {
 348         if ( mixbuf != NULL ) {
 349                 SDL_FreeAudioMem(mixbuf);
 350                 mixbuf = NULL;
 351         }
 352         if ( pcm_handle ) {
 353                 SDL_NAME(snd_pcm_drain)(pcm_handle);
 354                 SDL_NAME(snd_pcm_close)(pcm_handle);
 355                 pcm_handle = NULL;
 356         }
 357 }
 358
 359 static int ALSA_finalize_hardware(_THIS, SDL_AudioSpec *spec, snd_pcm_hw_params_t *hwparams, int override)
 360 {
 361         int status;
 362         snd_pcm_uframes_t bufsize;
 363
 364         /* "set" the hardware with the desired parameters */
 365         status = SDL_NAME(snd_pcm_hw_params)(pcm_handle, hwparams);
 366         if ( status < 0 ) {
 367                 return(-1);
 368         }
 369
 370         /* Get samples for the actual buffer size */
 371         status = SDL_NAME(snd_pcm_hw_params_get_buffer_size)(hwparams, &bufsize);
 372         if ( status < 0 ) {
 373                 return(-1);
 374         }
 375         if ( !override && bufsize != spec->samples * 2 ) {
 376                 return(-1);
 377         }
 378
 379         /* FIXME: Is this safe to do? */
 380         spec->samples = bufsize / 2;
 381
 382         /* This is useful for debugging */
 383         if ( getenv("SDL_AUDIO_ALSA_DEBUG") ) {
 384                 snd_pcm_uframes_t persize = 0;
 385                 unsigned int periods = 0;
 386
 387                 SDL_NAME(snd_pcm_hw_params_get_period_size)(hwparams, &persize, NULL);
 388                 SDL_NAME(snd_pcm_hw_params_get_periods)(hwparams, &periods, NULL);
 389
 390                 fprintf(stderr, "ALSA: period size = %ld, periods = %u, buffer size = %lu\n", persize, periods, bufsize);
 391         }
 392         return(0);
 393 }
 394
 395 static int ALSA_set_period_size(_THIS, SDL_AudioSpec *spec, snd_pcm_hw_params_t *params, int override)
 396 {
 397         const char *env;
 398         int status;
 399         snd_pcm_hw_params_t *hwparams;
 400         snd_pcm_uframes_t frames;
 401         unsigned int periods;
 402
 403         /* Copy the hardware parameters for this setup */
 404         snd_pcm_hw_params_alloca(&hwparams);
 405         SDL_NAME(snd_pcm_hw_params_copy)(hwparams, params);
 406
 407         if ( !override ) {
 408                 env = getenv("SDL_AUDIO_ALSA_SET_PERIOD_SIZE");
 409                 if ( env ) {
 410                         override = SDL_atoi(env);
 411                         if ( override == 0 ) {
 412                                 return(-1);
 413                         }
 414                 }
 415         }
 416
 417         frames = spec->samples;
 418         status = SDL_NAME(snd_pcm_hw_params_set_period_size_near)(pcm_handle, hwparams, &frames, NULL);
 419         if ( status < 0 ) {
 420                 return(-1);
 421         }
 422
 423         periods = 2;
 424         status = SDL_NAME(snd_pcm_hw_params_set_periods_near)(pcm_handle, hwparams, &periods, NULL);
 425         if ( status < 0 ) {
 426                 return(-1);
 427         }
 428
 429         return ALSA_finalize_hardware(this, spec, hwparams, override);
 430 }
 431
 432 static int ALSA_set_buffer_size(_THIS, SDL_AudioSpec *spec, snd_pcm_hw_params_t *params, int override)
 433 {
 434         const char *env;
 435         int status;
 436         snd_pcm_hw_params_t *hwparams;
 437         snd_pcm_uframes_t frames;
 438
 439         /* Copy the hardware parameters for this setup */
 440         snd_pcm_hw_params_alloca(&hwparams);
 441         SDL_NAME(snd_pcm_hw_params_copy)(hwparams, params);
 442
 443         if ( !override ) {
 444                 env = getenv("SDL_AUDIO_ALSA_SET_BUFFER_SIZE");
 445                 if ( env ) {
 446                         override = SDL_atoi(env);
 447                         if ( override == 0 ) {
 448                                 return(-1);
 449                         }
 450                 }
 451         }
 452
 453         frames = spec->samples * 2;
 454         status = SDL_NAME(snd_pcm_hw_params_set_buffer_size_near)(pcm_handle, hwparams, &frames);
 455         if ( status < 0 ) {
 456                 return(-1);
 457         }
 458
 459         return ALSA_finalize_hardware(this, spec, hwparams, override);
 460 }
 461
 462 static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec)
 463 {
 464         int                  status;
 465         snd_pcm_hw_params_t *hwparams;
 466         snd_pcm_sw_params_t *swparams;
 467         snd_pcm_format_t     format;
 468         unsigned int         rate;
 469         unsigned int         channels;
 470         Uint16               test_format;
 471
 472         /* Open the audio device */
 473         /* Name of device should depend on # channels in spec */
 474         status = SDL_NAME(snd_pcm_open)(&pcm_handle, get_audio_device(spec->channels), SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
 475
 476         if ( status < 0 ) {
 477                 SDL_SetError("Couldn't open audio device: %s", SDL_NAME(snd_strerror)(status));
 478                 return(-1);
 479         }
 480
 481         /* Figure out what the hardware is capable of */
 482         snd_pcm_hw_params_alloca(&hwparams);
 483         status = SDL_NAME(snd_pcm_hw_params_any)(pcm_handle, hwparams);
 484         if ( status < 0 ) {
 485                 SDL_SetError("Couldn't get hardware config: %s", SDL_NAME(snd_strerror)(status));
 486                 ALSA_CloseAudio(this);
 487                 return(-1);
 488         }
 489
 490         /* SDL only uses interleaved sample output */
 491         status = SDL_NAME(snd_pcm_hw_params_set_access)(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
 492         if ( status < 0 ) {
 493                 SDL_SetError("Couldn't set interleaved access: %s", SDL_NAME(snd_strerror)(status));
 494                 ALSA_CloseAudio(this);
 495                 return(-1);
 496         }
 497
 498         /* Try for a closest match on audio format */
 499         status = -1;
 500         for ( test_format = SDL_FirstAudioFormat(spec->format);
 501               test_format && (status < 0); ) {
 502                 switch ( test_format ) {
 503                         case AUDIO_U8:
 504                                 format = SND_PCM_FORMAT_U8;
 505                                 break;
 506                         case AUDIO_S8:
 507                                 format = SND_PCM_FORMAT_S8;
 508                                 break;
 509                         case AUDIO_S16LSB:
 510                                 format = SND_PCM_FORMAT_S16_LE;
 511                                 break;
 512                         case AUDIO_S16MSB:
 513                                 format = SND_PCM_FORMAT_S16_BE;
 514                                 break;
 515                         case AUDIO_U16LSB:
 516                                 format = SND_PCM_FORMAT_U16_LE;
 517                                 break;
 518                         case AUDIO_U16MSB:
 519                                 format = SND_PCM_FORMAT_U16_BE;
 520                                 break;
 521                         default:
 522                                 format = 0;
 523                                 break;
 524                 }
 525                 if ( format != 0 ) {
 526                         status = SDL_NAME(snd_pcm_hw_params_set_format)(pcm_handle, hwparams, format);
 527                 }
 528                 if ( status < 0 ) {
 529                         test_format = SDL_NextAudioFormat();
 530                 }
 531         }
 532         if ( status < 0 ) {
 533                 SDL_SetError("Couldn't find any hardware audio formats");
 534                 ALSA_CloseAudio(this);
 535                 return(-1);
 536         }
 537         spec->format = test_format;
 538
 539         /* Set the number of channels */
 540         status = SDL_NAME(snd_pcm_hw_params_set_channels)(pcm_handle, hwparams, spec->channels);
 541         channels = spec->channels;
 542         if ( status < 0 ) {
 543                 status = SDL_NAME(snd_pcm_hw_params_get_channels)(hwparams, &channels);
 544                 if ( status < 0 ) {
 545                         SDL_SetError("Couldn't set audio channels");
 546                         ALSA_CloseAudio(this);
 547                         return(-1);
 548                 }
 549                 spec->channels = channels;
 550         }
 551
 552         /* Set the audio rate */
 553         rate = spec->freq;
 554
 555         status = SDL_NAME(snd_pcm_hw_params_set_rate_near)(pcm_handle, hwparams, &rate, NULL);
 556         if ( status < 0 ) {
 557                 SDL_SetError("Couldn't set audio frequency: %s", SDL_NAME(snd_strerror)(status));
 558                 ALSA_CloseAudio(this);
 559                 return(-1);
 560         }
 561         spec->freq = rate;
 562
 563         /* Set the buffer size, in samples */
 564         if ( ALSA_set_period_size(this, spec, hwparams, 0) < 0 &&
 565              ALSA_set_buffer_size(this, spec, hwparams, 0) < 0 ) {
 566                 /* Failed to set desired buffer size, do the best you can... */
 567                 if ( ALSA_set_period_size(this, spec, hwparams, 1) < 0 ) {
 568                         SDL_SetError("Couldn't set hardware audio parameters: %s", SDL_NAME(snd_strerror)(status));
 569                         ALSA_CloseAudio(this);
 570                         return(-1);
 571                 }
 572         }
 573
 574         /* Set the software parameters */
 575         snd_pcm_sw_params_alloca(&swparams);
 576         status = SDL_NAME(snd_pcm_sw_params_current)(pcm_handle, swparams);
 577         if ( status < 0 ) {
 578                 SDL_SetError("Couldn't get software config: %s", SDL_NAME(snd_strerror)(status));
 579                 ALSA_CloseAudio(this);
 580                 return(-1);
 581         }
 582         status = SDL_NAME(snd_pcm_sw_params_set_start_threshold)(pcm_handle, swparams, 1);
 583         if ( status < 0 ) {
 584                 SDL_SetError("Couldn't set start threshold: %s", SDL_NAME(snd_strerror)(status));
 585                 ALSA_CloseAudio(this);
 586                 return(-1);
 587         }
 588         status = SDL_NAME(snd_pcm_sw_params)(pcm_handle, swparams);
 589         if ( status < 0 ) {
 590                 SDL_SetError("Couldn't set software audio parameters: %s", SDL_NAME(snd_strerror)(status));
 591                 ALSA_CloseAudio(this);
 592                 return(-1);
 593         }
 594
 595         /* Calculate the final parameters for this audio specification */
 596         SDL_CalculateAudioSpec(spec);
 597
 598         /* Allocate mixing buffer */
 599         mixlen = spec->size;
 600         mixbuf = (Uint8 *)SDL_AllocAudioMem(mixlen);
 601         if ( mixbuf == NULL ) {
 602                 ALSA_CloseAudio(this);
 603                 return(-1);
 604         }
 605         SDL_memset(mixbuf, spec->silence, spec->size);
 606
 607         /* Switch to blocking mode for playback */
 608         SDL_NAME(snd_pcm_nonblock)(pcm_handle, 0);
 609
 610         /* We're ready to rock and roll. :-) */
 611         return(0);
 612 }