src/audio/alsa/SDL_alsa_audio.c

   1 /*
   2     SDL - Simple DirectMedia Layer
   3     Copyright (C) 1997-2012 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_set_avail_min))(snd_pcm_t *pcm, snd_pcm_sw_params_t *swparams, snd_pcm_uframes_t val);
  85 static int (*SDL_NAME(snd_pcm_sw_params_current))(snd_pcm_t *pcm, snd_pcm_sw_params_t *swparams);
  86 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);
  87 static int (*SDL_NAME(snd_pcm_sw_params))(snd_pcm_t *pcm, snd_pcm_sw_params_t *params);
  88 static int (*SDL_NAME(snd_pcm_nonblock))(snd_pcm_t *pcm, int nonblock);
  89 static int (*SDL_NAME(snd_pcm_wait))(snd_pcm_t *pcm, int timeout);
  90 #define snd_pcm_hw_params_sizeof SDL_NAME(snd_pcm_hw_params_sizeof)
  91 #define snd_pcm_sw_params_sizeof SDL_NAME(snd_pcm_sw_params_sizeof)
  92
  93 /* cast funcs to char* first, to please GCC's strict aliasing rules. */
  94 static struct {
  95         const char *name;
  96         void **func;
  97 } alsa_functions[] = {
  98         { "snd_pcm_open",       (void**)(char*)&SDL_NAME(snd_pcm_open)          },
  99         { "snd_pcm_close",      (void**)(char*)&SDL_NAME(snd_pcm_close) },
 100         { "snd_pcm_writei",     (void**)(char*)&SDL_NAME(snd_pcm_writei)        },
 101         { "snd_pcm_recover",    (void**)(char*)&SDL_NAME(snd_pcm_recover)       },
 102         { "snd_pcm_prepare",    (void**)(char*)&SDL_NAME(snd_pcm_prepare)       },
 103         { "snd_pcm_drain",      (void**)(char*)&SDL_NAME(snd_pcm_drain) },
 104         { "snd_strerror",       (void**)(char*)&SDL_NAME(snd_strerror)          },
 105         { "snd_pcm_hw_params_sizeof",           (void**)(char*)&SDL_NAME(snd_pcm_hw_params_sizeof)              },
 106         { "snd_pcm_sw_params_sizeof",           (void**)(char*)&SDL_NAME(snd_pcm_sw_params_sizeof)              },
 107         { "snd_pcm_hw_params_copy",             (void**)(char*)&SDL_NAME(snd_pcm_hw_params_copy)                },
 108         { "snd_pcm_hw_params_any",              (void**)(char*)&SDL_NAME(snd_pcm_hw_params_any)         },
 109         { "snd_pcm_hw_params_set_access",       (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_access)          },
 110         { "snd_pcm_hw_params_set_format",       (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_format)          },
 111         { "snd_pcm_hw_params_set_channels",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_channels)        },
 112         { "snd_pcm_hw_params_get_channels",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_channels)        },
 113         { "snd_pcm_hw_params_set_rate_near",    (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_rate_near)       },
 114         { "snd_pcm_hw_params_set_period_size_near",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_period_size_near)        },
 115         { "snd_pcm_hw_params_get_period_size",  (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_period_size)     },
 116         { "snd_pcm_hw_params_set_periods_near", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_periods_near)    },
 117         { "snd_pcm_hw_params_get_periods",      (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_periods) },
 118         { "snd_pcm_hw_params_set_buffer_size_near",     (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_buffer_size_near) },
 119         { "snd_pcm_hw_params_get_buffer_size",  (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_buffer_size) },
 120         { "snd_pcm_hw_params",  (void**)(char*)&SDL_NAME(snd_pcm_hw_params)     },
 121         { "snd_pcm_sw_params_set_avail_min",    (void**)(char*)&SDL_NAME(snd_pcm_sw_params_set_avail_min) },
 122         { "snd_pcm_sw_params_current",  (void**)(char*)&SDL_NAME(snd_pcm_sw_params_current)     },
 123         { "snd_pcm_sw_params_set_start_threshold",      (void**)(char*)&SDL_NAME(snd_pcm_sw_params_set_start_threshold) },
 124         { "snd_pcm_sw_params",  (void**)(char*)&SDL_NAME(snd_pcm_sw_params)     },
 125         { "snd_pcm_nonblock",   (void**)(char*)&SDL_NAME(snd_pcm_nonblock)      },
 126         { "snd_pcm_wait",       (void**)(char*)&SDL_NAME(snd_pcm_wait)  },
 127 };
 128
 129 static void UnloadALSALibrary(void) {
 130         if (alsa_loaded) {
 131                 SDL_UnloadObject(alsa_handle);
 132                 alsa_handle = NULL;
 133                 alsa_loaded = 0;
 134         }
 135 }
 136
 137 static int LoadALSALibrary(void) {
 138         int i, retval = -1;
 139
 140         alsa_handle = SDL_LoadObject(alsa_library);
 141         if (alsa_handle) {
 142                 alsa_loaded = 1;
 143                 retval = 0;
 144                 for (i = 0; i < SDL_arraysize(alsa_functions); i++) {
 145                         *alsa_functions[i].func = SDL_LoadFunction(alsa_handle,alsa_functions[i].name);
 146                         if (!*alsa_functions[i].func) {
 147                                 retval = -1;
 148                                 UnloadALSALibrary();
 149                                 break;
 150                         }
 151                 }
 152         }
 153         return retval;
 154 }
 155
 156 #else
 157
 158 static void UnloadALSALibrary(void) {
 159         return;
 160 }
 161
 162 static int LoadALSALibrary(void) {
 163         return 0;
 164 }
 165
 166 #endif /* SDL_AUDIO_DRIVER_ALSA_DYNAMIC */
 167
 168 static const char *get_audio_device(int channels)
 169 {
 170         const char *device;
 171
 172         device = SDL_getenv("AUDIODEV");        /* Is there a standard variable name? */
 173         if ( device == NULL ) {
 174                 switch (channels) {
 175                 case 6:
 176                         device = "plug:surround51";
 177                         break;
 178                 case 4:
 179                         device = "plug:surround40";
 180                         break;
 181                 default:
 182                         device = "default";
 183                         break;
 184                 }
 185         }
 186         return device;
 187 }
 188
 189 /* Audio driver bootstrap functions */
 190
 191 static int Audio_Available(void)
 192 {
 193         int available;
 194         int status;
 195         snd_pcm_t *handle;
 196
 197         available = 0;
 198         if (LoadALSALibrary() < 0) {
 199                 return available;
 200         }
 201         status = SDL_NAME(snd_pcm_open)(&handle, get_audio_device(2), SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
 202         if ( status >= 0 ) {
 203                 available = 1;
 204                 SDL_NAME(snd_pcm_close)(handle);
 205         }
 206         UnloadALSALibrary();
 207         return(available);
 208 }
 209
 210 static void Audio_DeleteDevice(SDL_AudioDevice *device)
 211 {
 212         SDL_free(device->hidden);
 213         SDL_free(device);
 214         UnloadALSALibrary();
 215 }
 216
 217 static SDL_AudioDevice *Audio_CreateDevice(int devindex)
 218 {
 219         SDL_AudioDevice *this;
 220
 221         /* Initialize all variables that we clean on shutdown */
 222         LoadALSALibrary();
 223         this = (SDL_AudioDevice *)SDL_malloc(sizeof(SDL_AudioDevice));
 224         if ( this ) {
 225                 SDL_memset(this, 0, (sizeof *this));
 226                 this->hidden = (struct SDL_PrivateAudioData *)
 227                                 SDL_malloc((sizeof *this->hidden));
 228         }
 229         if ( (this == NULL) || (this->hidden == NULL) ) {
 230                 SDL_OutOfMemory();
 231                 if ( this ) {
 232                         SDL_free(this);
 233                 }
 234                 return(0);
 235         }
 236         SDL_memset(this->hidden, 0, (sizeof *this->hidden));
 237
 238         /* Set the function pointers */
 239         this->OpenAudio = ALSA_OpenAudio;
 240         this->WaitAudio = ALSA_WaitAudio;
 241         this->PlayAudio = ALSA_PlayAudio;
 242         this->GetAudioBuf = ALSA_GetAudioBuf;
 243         this->CloseAudio = ALSA_CloseAudio;
 244
 245         this->free = Audio_DeleteDevice;
 246
 247         return this;
 248 }
 249
 250 AudioBootStrap ALSA_bootstrap = {
 251         DRIVER_NAME, "ALSA PCM audio",
 252         Audio_Available, Audio_CreateDevice
 253 };
 254
 255 /* This function waits until it is possible to write a full sound buffer */
 256 static void ALSA_WaitAudio(_THIS)
 257 {
 258         /* We're in blocking mode, so there's nothing to do here */
 259 }
 260
 261
 262 /*
 263  * http://bugzilla.libsdl.org/show_bug.cgi?id=110
 264  * "For Linux ALSA, this is FL-FR-RL-RR-C-LFE
 265  *  and for Windows DirectX [and CoreAudio], this is FL-FR-C-LFE-RL-RR"
 266  */
 267 #define SWIZ6(T) \
 268     T *ptr = (T *) mixbuf; \
 269     Uint32 i; \
 270     for (i = 0; i < this->spec.samples; i++, ptr += 6) { \
 271         T tmp; \
 272         tmp = ptr[2]; ptr[2] = ptr[4]; ptr[4] = tmp; \
 273         tmp = ptr[3]; ptr[3] = ptr[5]; ptr[5] = tmp; \
 274     }
 275
 276 static __inline__ void swizzle_alsa_channels_6_64bit(_THIS) { SWIZ6(Uint64); }
 277 static __inline__ void swizzle_alsa_channels_6_32bit(_THIS) { SWIZ6(Uint32); }
 278 static __inline__ void swizzle_alsa_channels_6_16bit(_THIS) { SWIZ6(Uint16); }
 279 static __inline__ void swizzle_alsa_channels_6_8bit(_THIS) { SWIZ6(Uint8); }
 280
 281 #undef SWIZ6
 282
 283
 284 /*
 285  * Called right before feeding this->mixbuf to the hardware. Swizzle channels
 286  *  from Windows/Mac order to the format alsalib will want.
 287  */
 288 static __inline__ void swizzle_alsa_channels(_THIS)
 289 {
 290     if (this->spec.channels == 6) {
 291         const Uint16 fmtsize = (this->spec.format & 0xFF); /* bits/channel. */
 292         if (fmtsize == 16)
 293             swizzle_alsa_channels_6_16bit(this);
 294         else if (fmtsize == 8)
 295             swizzle_alsa_channels_6_8bit(this);
 296         else if (fmtsize == 32)
 297             swizzle_alsa_channels_6_32bit(this);
 298         else if (fmtsize == 64)
 299             swizzle_alsa_channels_6_64bit(this);
 300     }
 301
 302     /* !!! FIXME: update this for 7.1 if needed, later. */
 303 }
 304
 305
 306 static void ALSA_PlayAudio(_THIS)
 307 {
 308         int status;
 309         snd_pcm_uframes_t frames_left;
 310         const Uint8 *sample_buf = (const Uint8 *) mixbuf;
 311         const int frame_size = (((int) (this->spec.format & 0xFF)) / 8) * this->spec.channels;
 312
 313         swizzle_alsa_channels(this);
 314
 315         frames_left = ((snd_pcm_uframes_t) this->spec.samples);
 316
 317         while ( frames_left > 0 && this->enabled ) {
 318                 /* This works, but needs more testing before going live */
 319                 /*SDL_NAME(snd_pcm_wait)(pcm_handle, -1);*/
 320
 321                 status = SDL_NAME(snd_pcm_writei)(pcm_handle, sample_buf, frames_left);
 322                 if ( status < 0 ) {
 323                         if ( status == -EAGAIN ) {
 324                                 /* Apparently snd_pcm_recover() doesn't handle this case - does it assume snd_pcm_wait() above? */
 325                                 SDL_Delay(1);
 326                                 continue;
 327                         }
 328                         status = SDL_NAME(snd_pcm_recover)(pcm_handle, status, 0);
 329                         if ( status < 0 ) {
 330                                 /* Hmm, not much we can do - abort */
 331                                 fprintf(stderr, "ALSA write failed (unrecoverable): %s\n", SDL_NAME(snd_strerror)(status));
 332                                 this->enabled = 0;
 333                                 return;
 334                         }
 335                         continue;
 336                 }
 337                 sample_buf += status * frame_size;
 338                 frames_left -= status;
 339         }
 340 }
 341
 342 static Uint8 *ALSA_GetAudioBuf(_THIS)
 343 {
 344         return(mixbuf);
 345 }
 346
 347 static void ALSA_CloseAudio(_THIS)
 348 {
 349         if ( mixbuf != NULL ) {
 350                 SDL_FreeAudioMem(mixbuf);
 351                 mixbuf = NULL;
 352         }
 353         if ( pcm_handle ) {
 354                 SDL_NAME(snd_pcm_drain)(pcm_handle);
 355                 SDL_NAME(snd_pcm_close)(pcm_handle);
 356                 pcm_handle = NULL;
 357         }
 358 }
 359
 360 static int ALSA_finalize_hardware(_THIS, SDL_AudioSpec *spec, snd_pcm_hw_params_t *hwparams, int override)
 361 {
 362         int status;
 363         snd_pcm_uframes_t bufsize;
 364
 365         /* "set" the hardware with the desired parameters */
 366         status = SDL_NAME(snd_pcm_hw_params)(pcm_handle, hwparams);
 367         if ( status < 0 ) {
 368                 return(-1);
 369         }
 370
 371         /* Get samples for the actual buffer size */
 372         status = SDL_NAME(snd_pcm_hw_params_get_buffer_size)(hwparams, &bufsize);
 373         if ( status < 0 ) {
 374                 return(-1);
 375         }
 376         if ( !override && bufsize != spec->samples * 2 ) {
 377                 return(-1);
 378         }
 379
 380         /* FIXME: Is this safe to do? */
 381         spec->samples = bufsize / 2;
 382
 383         /* This is useful for debugging */
 384         if ( getenv("SDL_AUDIO_ALSA_DEBUG") ) {
 385                 snd_pcm_uframes_t persize = 0;
 386                 unsigned int periods = 0;
 387
 388                 SDL_NAME(snd_pcm_hw_params_get_period_size)(hwparams, &persize, NULL);
 389                 SDL_NAME(snd_pcm_hw_params_get_periods)(hwparams, &periods, NULL);
 390
 391                 fprintf(stderr, "ALSA: period size = %ld, periods = %u, buffer size = %lu\n", persize, periods, bufsize);
 392         }
 393         return(0);
 394 }
 395
 396 static int ALSA_set_period_size(_THIS, SDL_AudioSpec *spec, snd_pcm_hw_params_t *params, int override)
 397 {
 398         const char *env;
 399         int status;
 400         snd_pcm_hw_params_t *hwparams;
 401         snd_pcm_uframes_t frames;
 402         unsigned int periods;
 403
 404         /* Copy the hardware parameters for this setup */
 405         snd_pcm_hw_params_alloca(&hwparams);
 406         SDL_NAME(snd_pcm_hw_params_copy)(hwparams, params);
 407
 408         if ( !override ) {
 409                 env = getenv("SDL_AUDIO_ALSA_SET_PERIOD_SIZE");
 410                 if ( env ) {
 411                         override = SDL_atoi(env);
 412                         if ( override == 0 ) {
 413                                 return(-1);
 414                         }
 415                 }
 416         }
 417
 418         frames = spec->samples;
 419         status = SDL_NAME(snd_pcm_hw_params_set_period_size_near)(pcm_handle, hwparams, &frames, NULL);
 420         if ( status < 0 ) {
 421                 return(-1);
 422         }
 423
 424         periods = 2;
 425         status = SDL_NAME(snd_pcm_hw_params_set_periods_near)(pcm_handle, hwparams, &periods, NULL);
 426         if ( status < 0 ) {
 427                 return(-1);
 428         }
 429
 430         return ALSA_finalize_hardware(this, spec, hwparams, override);
 431 }
 432
 433 static int ALSA_set_buffer_size(_THIS, SDL_AudioSpec *spec, snd_pcm_hw_params_t *params, int override)
 434 {
 435         const char *env;
 436         int status;
 437         snd_pcm_hw_params_t *hwparams;
 438         snd_pcm_uframes_t frames;
 439
 440         /* Copy the hardware parameters for this setup */
 441         snd_pcm_hw_params_alloca(&hwparams);
 442         SDL_NAME(snd_pcm_hw_params_copy)(hwparams, params);
 443
 444         if ( !override ) {
 445                 env = getenv("SDL_AUDIO_ALSA_SET_BUFFER_SIZE");
 446                 if ( env ) {
 447                         override = SDL_atoi(env);
 448                         if ( override == 0 ) {
 449                                 return(-1);
 450                         }
 451                 }
 452         }
 453
 454         frames = spec->samples * 2;
 455         status = SDL_NAME(snd_pcm_hw_params_set_buffer_size_near)(pcm_handle, hwparams, &frames);
 456         if ( status < 0 ) {
 457                 return(-1);
 458         }
 459
 460         return ALSA_finalize_hardware(this, spec, hwparams, override);
 461 }
 462
 463 static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec)
 464 {
 465         int                  status;
 466         snd_pcm_hw_params_t *hwparams;
 467         snd_pcm_sw_params_t *swparams;
 468         snd_pcm_format_t     format;
 469         unsigned int         rate;
 470         unsigned int         channels;
 471         Uint16               test_format;
 472
 473         /* Open the audio device */
 474         /* Name of device should depend on # channels in spec */
 475         status = SDL_NAME(snd_pcm_open)(&pcm_handle, get_audio_device(spec->channels), SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK);
 476
 477         if ( status < 0 ) {
 478                 SDL_SetError("Couldn't open audio device: %s", SDL_NAME(snd_strerror)(status));
 479                 return(-1);
 480         }
 481
 482         /* Figure out what the hardware is capable of */
 483         snd_pcm_hw_params_alloca(&hwparams);
 484         status = SDL_NAME(snd_pcm_hw_params_any)(pcm_handle, hwparams);
 485         if ( status < 0 ) {
 486                 SDL_SetError("Couldn't get hardware config: %s", SDL_NAME(snd_strerror)(status));
 487                 ALSA_CloseAudio(this);
 488                 return(-1);
 489         }
 490
 491         /* SDL only uses interleaved sample output */
 492         status = SDL_NAME(snd_pcm_hw_params_set_access)(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
 493         if ( status < 0 ) {
 494                 SDL_SetError("Couldn't set interleaved access: %s", SDL_NAME(snd_strerror)(status));
 495                 ALSA_CloseAudio(this);
 496                 return(-1);
 497         }
 498
 499         /* Try for a closest match on audio format */
 500         status = -1;
 501         for ( test_format = SDL_FirstAudioFormat(spec->format);
 502               test_format && (status < 0); ) {
 503                 switch ( test_format ) {
 504                         case AUDIO_U8:
 505                                 format = SND_PCM_FORMAT_U8;
 506                                 break;
 507                         case AUDIO_S8:
 508                                 format = SND_PCM_FORMAT_S8;
 509                                 break;
 510                         case AUDIO_S16LSB:
 511                                 format = SND_PCM_FORMAT_S16_LE;
 512                                 break;
 513                         case AUDIO_S16MSB:
 514                                 format = SND_PCM_FORMAT_S16_BE;
 515                                 break;
 516                         case AUDIO_U16LSB:
 517                                 format = SND_PCM_FORMAT_U16_LE;
 518                                 break;
 519                         case AUDIO_U16MSB:
 520                                 format = SND_PCM_FORMAT_U16_BE;
 521                                 break;
 522                         default:
 523                                 format = 0;
 524                                 break;
 525                 }
 526                 if ( format != 0 ) {
 527                         status = SDL_NAME(snd_pcm_hw_params_set_format)(pcm_handle, hwparams, format);
 528                 }
 529                 if ( status < 0 ) {
 530                         test_format = SDL_NextAudioFormat();
 531                 }
 532         }
 533         if ( status < 0 ) {
 534                 SDL_SetError("Couldn't find any hardware audio formats");
 535                 ALSA_CloseAudio(this);
 536                 return(-1);
 537         }
 538         spec->format = test_format;
 539
 540         /* Set the number of channels */
 541         status = SDL_NAME(snd_pcm_hw_params_set_channels)(pcm_handle, hwparams, spec->channels);
 542         channels = spec->channels;
 543         if ( status < 0 ) {
 544                 status = SDL_NAME(snd_pcm_hw_params_get_channels)(hwparams, &channels);
 545                 if ( status < 0 ) {
 546                         SDL_SetError("Couldn't set audio channels");
 547                         ALSA_CloseAudio(this);
 548                         return(-1);
 549                 }
 550                 spec->channels = channels;
 551         }
 552
 553         /* Set the audio rate */
 554         rate = spec->freq;
 555
 556         status = SDL_NAME(snd_pcm_hw_params_set_rate_near)(pcm_handle, hwparams, &rate, NULL);
 557         if ( status < 0 ) {
 558                 SDL_SetError("Couldn't set audio frequency: %s", SDL_NAME(snd_strerror)(status));
 559                 ALSA_CloseAudio(this);
 560                 return(-1);
 561         }
 562         spec->freq = rate;
 563
 564         /* Set the buffer size, in samples */
 565         if ( ALSA_set_period_size(this, spec, hwparams, 0) < 0 &&
 566              ALSA_set_buffer_size(this, spec, hwparams, 0) < 0 ) {
 567                 /* Failed to set desired buffer size, do the best you can... */
 568                 if ( ALSA_set_period_size(this, spec, hwparams, 1) < 0 ) {
 569                         SDL_SetError("Couldn't set hardware audio parameters: %s", SDL_NAME(snd_strerror)(status));
 570                         ALSA_CloseAudio(this);
 571                         return(-1);
 572                 }
 573         }
 574
 575         /* Set the software parameters */
 576         snd_pcm_sw_params_alloca(&swparams);
 577         status = SDL_NAME(snd_pcm_sw_params_current)(pcm_handle, swparams);
 578         if ( status < 0 ) {
 579                 SDL_SetError("Couldn't get software config: %s", SDL_NAME(snd_strerror)(status));
 580                 ALSA_CloseAudio(this);
 581                 return(-1);
 582         }
 583         status = SDL_NAME(snd_pcm_sw_params_set_avail_min)(pcm_handle, swparams, spec->samples);
 584         if ( status < 0 ) {
 585                 SDL_SetError("Couldn't set minimum available samples: %s", SDL_NAME(snd_strerror)(status));
 586                 ALSA_CloseAudio(this);
 587                 return(-1);
 588         }
 589         status = SDL_NAME(snd_pcm_sw_params_set_start_threshold)(pcm_handle, swparams, 1);
 590         if ( status < 0 ) {
 591                 SDL_SetError("Couldn't set start threshold: %s", SDL_NAME(snd_strerror)(status));
 592                 ALSA_CloseAudio(this);
 593                 return(-1);
 594         }
 595         status = SDL_NAME(snd_pcm_sw_params)(pcm_handle, swparams);
 596         if ( status < 0 ) {
 597                 SDL_SetError("Couldn't set software audio parameters: %s", SDL_NAME(snd_strerror)(status));
 598                 ALSA_CloseAudio(this);
 599                 return(-1);
 600         }
 601
 602         /* Calculate the final parameters for this audio specification */
 603         SDL_CalculateAudioSpec(spec);
 604
 605         /* Allocate mixing buffer */
 606         mixlen = spec->size;
 607         mixbuf = (Uint8 *)SDL_AllocAudioMem(mixlen);
 608         if ( mixbuf == NULL ) {
 609                 ALSA_CloseAudio(this);
 610                 return(-1);
 611         }
 612         SDL_memset(mixbuf, spec->silence, spec->size);
 613
 614         /* Switch to blocking mode for playback */
 615         SDL_NAME(snd_pcm_nonblock)(pcm_handle, 0);
 616
 617         /* We're ready to rock and roll. :-) */
 618         return(0);
 619 }