The classD driver DOES register itself as /dev/audio/pcm0, and works correctly
as such with nx_player.
The conversions are wav (or mp3 etc) to pcm.
Don’t if we’re talking cross purposes or the classd driver works in a way it
shouldn’t!!!
> On 27 Aug 2023, at 23:00, Gregory Nutt <spudan...@gmail.com> wrote:
>
> Also, I don't think the /dev/audio/pcm0 device you are talking about is what
> you think it is. It is a character driver but not the Class D lower half.
> So, yes it can be opened.
>
> /Caveat: It has been ages since I worked with the audio subsystem so I might
> be completely wrong./
>
> /dev/audio/pcm0 is the audio subsystem interface device. The "pcm"
> indicates that it used the PCM software decoder (that will convert PCM file
> data to WAV). It gets set up like:
>
> boards/arm/sama5/sama5d4-ek/src/sam_wm8904.c:
>
> pcm = pcm_decode_initialize(wm8904);
> snprintf(devname, 12, "pcm%d", minor);
> ret = audio_register(devname, pcm);
>
> And a character driver is registered by the audio subsystem in audio/audio.c:
>
> int audio_register(FAR const char *name, FAR struct
> audio_lowerhalf_s *dev)
> {
> ...
>
> audinfo("Registering %s\n", path);
> return register_driver(path, &g_audioops, 0666, upper);
> }
>
> Where g_audioops is the character driver operations structure:
>
> static const struct file_operations g_audioops =
> {
> audio_open, /* open */
> audio_close, /* close */
> audio_read, /* read */
> audio_write, /* write */
> NULL, /* seek */
> audio_ioctl, /* ioctl */
> };
>
> So the registered pcm0 is the standard audio buffer chain configured for PCM
> file to WAV conversion and terminating with a wm8904 DAC.
>
> I don't believe that there is any way to get the Class D audio_ops_s as a
> driver under /dev. Nothing like that is supported.
>
