alsa接口

Posted 2020-12-07 renhl

■ 基本流程

打开设备

设置参数

获取fd

poll

写入数据/读取数据

关闭

 

■ 写入数据

snd_pcm_open(&u->pcm_handle, dev = pa_modargs_get_value(ma, "device", DEFAULT_DEVICE), SND_PCM_STREAM_PLAYBACK, SND_PCM_NONBLOCK)

snd_pcm_hw_params_malloc(&hwparams)
snd_pcm_hw_params_any(pcm_handle, hwparams)
snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED)
snd_pcm_hw_params_set_format(pcm_handle, hwparams, format_trans[ss->format])
snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &ss->rate, NULL)
snd_pcm_hw_params_set_channels(pcm_handle, hwparams, ss->channels)
snd_pcm_hw_params_set_periods_near(pcm_handle, hwparams, periods, NULL)
snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, buffer_size)
snd_pcm_hw_params(pcm_handle, hwparams)
snd_pcm_hw_params_free(hwparams)

*n_io_sources = snd_pcm_poll_descriptors_count(pcm_handle)
snd_pcm_poll_descriptors(pcm_handle, pfds, *n_io_sources)

poll

snd_pcm_prepare(u->pcm_handle)
snd_pcm_writei(u->pcm_handle, memchunk->memblock->data + memchunk->index, memchunk->length / u->frame_size)

snd_pcm_drop(u->pcm_handle)
snd_pcm_close(u->pcm_handle)

 

■ 读取数据

snd_pcm_open(&u->pcm_handle, dev = pa_modargs_get_value(ma, "device", DEFAULT_DEVICE), SND_PCM_STREAM_CAPTURE, SND_PCM_NONBLOCK) < 0) {


snd_pcm_hw_params_malloc(&hwparams)
snd_pcm_hw_params_any(pcm_handle, hwparams)
snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED)
snd_pcm_hw_params_set_format(pcm_handle, hwparams, format_trans[ss->format])
snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &ss->rate, NULL)
snd_pcm_hw_params_set_channels(pcm_handle, hwparams, ss->channels)
snd_pcm_hw_params_set_periods_near(pcm_handle, hwparams, periods, NULL)
snd_pcm_hw_params_set_buffer_size_near(pcm_handle, hwparams, buffer_size)
snd_pcm_hw_params(pcm_handle, hwparams)
snd_pcm_hw_params_free(hwparams)


snd_pcm_poll_descriptors_count(pcm_handle)
snd_pcm_poll_descriptors(pcm_handle, pfds, *n_io_sources)


poll

snd_pcm_state(u->pcm_handle)
snd_pcm_prepare(u->pcm_handle)

snd_pcm_readi(u->pcm_handle, u->memchunk.memblock->data + u->memchunk.index, u->memchunk.length / u->frame_size))

snd_pcm_drop(u->pcm_handle);
snd_pcm_close(u->pcm_handle);