sound/soc/dpcm.rst

47 modem. This sound card exposes 4 DSP front end (FE) ALSA PCM devices and
48 supports 6 back end (BE) DAIs. Each FE PCM can digitally route audio data to any
49 of the BE DAIs. The FE PCM devices can also route audio to more than 1 BE DAI.
119 1. Define the FE and BE DAI links.
121 2. Define any FE/BE PCM operations.
126 FE and BE DAI links
146 For the example above we have to define 4 FE DAI links and 6 BE DAI links. The
147 FE DAI links are defined as follows :-
162 	.....< other FE and BE DAI links here >
165 This FE DAI link is pretty similar to a regular DAI link except that we also
166 set the DAI link to a DPCM FE with the ``dynamic = 1``. The supported FE stream
169 each FE. This allows the ASoC core to trigger the DSP before or after the other
173 The FE DAI above sets the codec and code DAIs to dummy devices since the BE is
180 	.....< FE DAI links here >
231 FE/BE PCM operations
236 FE hw params. i.e. the DSP may perform SRC or ASRC from the FE to BE.
238 e.g. DSP converts all FE hw params to run at fixed rate of 48k, 16bit, stereo for
239 DAI0. This means all FE hw_params have to be fixed in the machine driver for
240 DAI0 so that the DAI is running at desired configuration regardless of the FE
252 	/* The DSP will convert the FE rate to 48k, stereo */
286 2. DAPM graph showing DSP audio routing from FE DAIs to BEs.
339  2. Hostless FE. This FE has a virtual connection to the BE DAI links on the DAPM
340     graph. Control is then carried out by the FE as regular PCM operations.
381 Hostless FE
384 The DAI link(s) are enabled by a FE that does not read or write any PCM data.
385 This means creating a new FE that is connected with a virtual path to both
386 DAI links. The DAI links will be started when the FE PCM is started and stopped
387 when the FE PCM is stopped. Note that the FE PCM cannot read or write data in