3.3 PCM stream playback

3.3.1 Stream playback mechanism

PCM stream playback is a method of playing back long PCM waveform data by continuously performing the process of writing the next waveform data at the end of playback while looping playback of PCM waveform data. Long PCM waveform data that can't fit into the sound memory, such as spoken voices, long sound effects, and recorded BGM, can be played back.
Since it is possible to know which part of the waveform data is currently being played back, the next waveform data is written to the part that has been played back. In the case as shown in the figure below, the next waveform data is written to the waveform data A part while the waveform data A has been played and the waveform data B is being played back. By repeating this process, any long waveform data can be played continuously.

3.3.2 PCM stream playback method

PCM stream playback should be performed according to the following procedure. Refer to “Chapter 4 Commands and Status” for details on how to issue sound control commands. In stereo, the following processing must be performed for the left and right channels.

order	processing
1	The first waveform data is transferred to the area of ​​waveform data A and waveform data B.
2	Sound control command “PCM start (85h)” is issued.
3	After playback of waveform data A, transfer the next waveform data to the area of ​​waveform data A .
4	After playback of waveform data B is finished, transfer the next waveform data to the area of ​​waveform data B .
5	Repeat steps 3 and 4
6	To end, issue the sound control command “PCM stop (86h)”.

  Note: Buffer size, transfer method, transfer timing, etc. are free to the main system.
Please select the most suitable method according to the situation without being bound by the procedure.