[linux-audio-dev] Set rate return zero

Hi everybody! I am a newbie to alsa programming. I am trying to follow the article which locates at http://www.suse.de/~mana/alsa090_howto.html to develop a playback program. My code here: snd_pcm_t*pcm_handle; unsigned int rate = 8000; // Sample rate returned by // snd_pcm_hw_params_set_rate_near int exact_rate; // exact_rate == rate ----> dir =0 //exact_rate < rate ----> dir =-1 //exact_rate > rate ----> dir =1 int dir = 0; // Number of periods int periods = 2; snd_pcm_stream_t stream = SND_PCM_STREAM_PLAYBACK; // This structure contains information about the hardware //and can be used to specify the configuration to be used for the PCM stream. snd_pcm_hw_params_t *hwparams; // Name of the PCM device, like plughw:0,0 //The first number is the number of the soundcard, //the second number is the number of the device. char *pcm_name; // Init pcm_name. Of course, later you //will make this configurable ;-) pcm_name = strdup("plughw:0,0"); printf("Device name:%s\n",pcm_name); //Allocate the snd_pcm_hw_params_t structure on the stack. snd_pcm_hw_params_alloca(&hwparams); // Open PCM. The last parameter of this function is the mode. // If this is set to 0, the standard mode is used. Possible // other values are SND_PCM_NONBLOCK and SND_PCM_ASYNC. // If SND_PCM_NONBLOCK is used, read / write access to the // PCM device will return immediately. If SND_PCM_ASYNC is // specified, SIGIO will be emitted whenever a period has //been completely processed by the soundcard. if (snd_pcm_open(&pcm_handle, pcm_name, stream, 0) < 0){//SND_PCM_NONBLOCK fprintf(stderr, "Error opening PCM device %s\n", pcm_name); return; } // Init hwparams with full configuration space if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) { fprintf(stderr, "Can not configure this PCM device.\n"); return; } // Set access type. This can be either SND_PCM_ACCESS_RW_INTERLEAVED or // SND_PCM_ACCESS_RW_NONINTERLEAVED.There are also access types for // MMAPed access, but this is beyond the scope of this introduction. if (snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) { fprintf(stderr, "Error setting access.\n"); return; } //Set sample format if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) { fprintf(stderr, "Error setting format.\n"); return; } // Set sample rate. If the exact rate is not supported by the hardware, use nearest possible rate. exact_rate = snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &rate, &dir); if (exact_rate < 0) { fprintf(stderr, "Error setting rate.\n"); return; } if (rate != exact_rate) { fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n=> Using %d Hz instead.\n", rate, exact_rate); } // Set number of channels if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) < 0) { fprintf(stderr, "Error setting channels.\n"); return; } // Set number of periods. Periods used to be called fragments. if (snd_pcm_hw_params_set_periods(pcm_handle, hwparams, periods, 0) < 0) { fprintf(stderr, "Error setting periods.\n"); return; } // Set buffer size (in frames). The resulting latency is given by // latency = periodsize * periods / (rate * bytes_per_frame) snd_pcm_uframes_t buffersize = ( snd_pcm_uframes_t )( number_of_frames * periods ); if (snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, &buffersize) < 0){ fprintf(stderr, "Error setting buffersize.\n"); return; } printf("Buffer size asked for %d, set %d \n",buffersize,exact_rate); // Apply HW parameter settings to // PCM device and prepare device if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) { fprintf(stderr, "Error setting HW params.\n"); return; } snd_pcm_prepare(pcm_handle); Unfortunately, exact_rate is zero.The following lines were printed out: The rate 8000 Hz is not supported by your hardware. => Using 0 Hz instead. If exact_rate > 0 is OK but it is zero. I don't know how to solve the problem. Please help me. Thanks! Phuoc Nguyen