PCM direct access Audio devices are opened exclusively for a selected direction. This does not allow open from more than one processes for the same audio device in the same direction, but does allow one open call to each playback direction and second open call to record direction independently. ALSA PCM API uses two operating modes - block and stream. The block mode uses an enhanced double buffering scheme. This allows the user to implement a more comfortable buffer setup.
Audio buffer is separated to small fragments.
Each fragment has the same size. The stream mode may be used for real-time audio applications. The driver allows to transfer data with the sample resolution. The process using the audio device in this mode is never blocked. Only one parameter for buffering is required - queue size.