Thank you for responding!
That is a great suggestion and i will be looking into it.
However, I have a concern about receiving a PWM interface. For PWM audio to
work, the PWM interface must give a hardware address to its compare
register.
I haven't seen that the PWM interface is providing one.
This address is required because we need DMA with a pacing timer to provide
samples to the PWM hardware address at a fixed sample rate.
If DMA is not used, it is going to be very hard to have a consistent sample
rate. Or even impossible.
-- DMA PWM --
[ Samplerate timer ]\
[ Sample memory ] ------> [ DMA ] --------> [ PWM compare register (not
provided) ]
I suppose a solution would be to give the audio device a pointer to one
directly without PWM interface.
Example pseudo code: audio_device = register( *pwm_compare_ptr, bitdepth,
dma_driver *dma );
However, looking into the pacing timer, that might be even arch specific as
well.
I hope someone has more knowledge about this.
Kind regards,
Kevin
Op ma 24 feb 2025 om 18:37 schreef Tiago Medicci Serrano <
tiago.medi...@gmail.com>:
> Hi!
>
> Tiago, since you are the audio guy, what do you think? Is it possible to
> > create the "fake" audio codec that works with PWM and DMA the way I'm
> > suggesting?
>
>
> Yes, the audio subsystem is created in layers. It wouldn't be a codec by
> itself (like PCM), but still can be understood as an *audio decoder
> driver*.
> Take `cs4344` audio decoder driver as an example. It receives a low-level
> I2S interface peripheral to be bound to the audio codec driver at
> `cs4344_initialize`
> <
> https://github.com/apache/incubator-nuttx/blob/4ef01d98d526361b9348646dd1fd09f3faff88c0/boards/xtensa/esp32s3/common/src/esp32s3_cs4344.c#L112
> >.
> After initialization, the PCM audio codec is created using this audio codec
> at `pcm_decode_initialize`
> <
> https://github.com/apache/incubator-nuttx/blob/4ef01d98d526361b9348646dd1fd09f3faff88c0/boards/xtensa/esp32s3/common/src/esp32s3_cs4344.c#L125
> >.
> Instead of the `cs4344` audio interface, there would be a "generic PWM
> audio codec" that received a PWM interface from the device and that
> generates the signal to be sent to the PWM peripheral. All the
> required translation (from PCM, for instance) would be done in this driver.
>
> Best regards,
>
> Em dom., 23 de fev. de 2025 às 07:10, Alan C. Assis <acas...@gmail.com>
> escreveu:
>
> > Hi Kevin,
> >
> > I think it is possible to create a generic audio using PWM and DMA, but
> it
> > will require two halves design (like many drivers in NuttX).
> >
> > The top half will implement the high end driver to be present like an
> > audio codec to the application (this way we don't need to modify existing
> > applications), and the bottom half will be responsible for setting up the
> > DMA channel to use with the PWM.
> >
> > Create a board only solution like you are thinking will work for your
> > board, but if in the future you move to another arch you will need to
> > reimplement it again and probably the way you are going to implement it
> the
> > existing applications cannot be used.
> >
> > Tiago, since you are the audio guy, what do you think? Is it possible to
> > create the "fake" audio codec that works with PWM and DMA the way I'm
> > suggesting?
> >
> > BR,
> >
> > Alan
> >
> > On Sun, Feb 23, 2025 at 6:59 AM Kevin Witteveen <kevinwit1...@gmail.com>
> > wrote:
> >
> >> Well that's unfortunate. It feels that this kind of system will not fit
> in
> >> this OS without a bit of hacking.
> >> I think I will implement this at board logic. Use DMAC.h device and
> >> directly use it on the PWM register addresses after initializing them
> the
> >> proper way using the PWM.h device.
> >> Maybe it's possible to add this as a source file to the common RP2040
> >> board
> >> directory for everyone to enjoy.
> >>
> >> About the I2S... yeah i think i will go for that next time. I am a
> little
> >> stuck with what I have on my PCB right now.
> >>
> >> Op zo 23 feb. 2025 02:20 schreef Tomek CEDRO <to...@cedro.info>:
> >>
> >> > Many people think about this but no solid implementation so far.. have
> >> > you consider I2S audio codec?
> >> > Tomek
> >> >
> >> >
> >> > On Sun, Feb 23, 2025 at 12:07 AM Kevin Witteveen <
> >> kevinwit1...@gmail.com>
> >> > wrote:
> >> > >
> >> > > Thanks, however I'm specifically looking for audio. For example,
> >> music,
> >> > > samples, etc. A tone is not enough for what I'm looking for.
> >> > > Or did I miss something and the audio_tone is actually more than
> just
> >> a
> >> > > tone?
> >> > >
> >> > > Op za 22 feb 2025 om 22:05 schreef TimH <t...@jti.uk.com.invalid>:
> >> > >
> >> > > > CONFIG_AUDIO_TONE?
> >> > > >
> >> > > > Not sure if that’s exactly what you’re after but could be?
> >> > > >
> >> > > > > On 22 Feb 2025, at 17:12, Kevin Witteveen <
> kevinwit1...@gmail.com
> >> >
> >> > > > wrote:
> >> > > > >
> >> > > > > Hi nuttx,
> >> > > > >
> >> > > > > I need an audio device that can generate sound using PWM on the
> >> > RP2040.
> >> > > > It
> >> > > > > appears nothing already exists for this.
> >> > > > > What would be a good way to implement this?
> >> > > > >
> >> > > > > My previous implementation outside NuttX was to use DMA to feed
> >> > samples
> >> > > > > into a PWM register. Relatively simple.
> >> > > > > However, in NuttX i now need to combine the PWM implementation
> >> with
> >> > the
> >> > > > > DMAC implementation. This is where I'm not sure how to "connect
> >> them
> >> > > > > together" on a proper "nuttx" way.
> >> > > > > Then also have it show up as an audio device.
> >> > > > >
> >> > > > > in case you wonder about the concept PWM audio. It is a common
> >> way to
> >> > > > > generate audio. It is how class-D amplifiers work. This is
> because
> >> > the
> >> > > > duty
> >> > > > > cycle of PWM when filtered becomes an analog signal. A very
> cheap
> >> > way to
> >> > > > > implement audio in systems.
> >> > > > >
> >> > > > > Are there any examples of projects out there that did this with
> >> > Nuttx?
> >> > > > > Or are there any people that have an idea how to take this
> project
> >> > on?
> >> > > > > Where do i begin? Where would i implement this? Board?
> >> Architecture?
> >> > > > >
> >> > > > > I would appreciate any help
> >> > > >
> >> > > >
> >> >
> >> >
> >> >
> >> > --
> >> > CeDeROM, SQ7MHZ, http://www.tomek.cedro.info
> >> >
> >>
> >
>
