On Tue, Sep 24, 2019 at 04:26:20PM +0200, Marc Gonzalez wrote: > On 24/09/2019 15:52, Charles Keepax wrote: > > > In general the ALSA framework doesn't really allow for stream > > params to change whilst the stream is active. Doing so is > > also normally very hard for the types of hardware usually > > involved. For example changing the clocks on a running I2S bus, > > very difficult to get both ends to pick up those changes at > > exactly the correct sample. Some newer buses like soundwire > > have more support for things like this were the ends of the > > link can synchronise changes but even there that is normally > > used for adding/removing streams from the bus, not reconfiguring > > a running stream. > > This jives with what "filt3r" wrote on #alsa-soc > > "at one point we were just closing the stream (somehow) if we detected > a change in e.g. sample-rate, so the user-space application would fail > on snd_pcm_readi()" > > snd_pcm_stop(p_spdif->capture_stream, SNDRV_PCM_STATE_DISCONNECTED); > Ah ok yeah that seems like a pretty good option to me thus forcing user-space to re-open at the new params. > > In your case above I would imagine the system would probably be > > setup where the DSP handles the conversion between the params > > requested from the receiver and those requested by user-space. > > One of the intentions of DPCM was to allow the backend > > (DSP-receiver here) to have different params to the frontend > > (DSP-userspace here). Although as you note you still probably > > need to add something to propagate those changes to the DSP. What > > form does the physical link between the receiver and the DSP > > take? > > The setup looks like this: > > A = Some kind of audio source, typically a TV or game console > B = The arm64 SoC, equipped with some nice speakers > > HDMI > A ------> B > > If we look inside B, we actually have > B1 = an eARC receiver (input = HDMI, output = I2S) > B2 = an audio DSP (input = I2S, output = speakers) > > I2S ? > B1 -----> B2 -----> speakers > > To answer your question, B1 and B2 are connected via I2S. > As yeah reconfiguring the I2S whilst it is running would be a terrifying prospect. Thanks, Charles _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
