Hi Mark, Takashi On Thu, Aug 3, 2023 at 9:11 PM Shengjiu Wang <shengjiu.wang@xxxxxxxxx> wrote: > > On Thu, Aug 3, 2023 at 1:28 AM Mark Brown <broonie@xxxxxxxxxx> wrote: > > > > On Wed, Aug 02, 2023 at 10:41:43PM +0800, Shengjiu Wang wrote: > > > > > Currently the ASRC in ALSA is to connect to another I2S device as > > > a sound card. But we'd like to the ASRC can be used by user space directly > > > that user space application can get the output after conversion from ASRC. > > > > That sort of use case would be handled via DPCM at the minute, though > > persuading it to connect two front ends together might be fun (which is > > the sort of reason why we want to push digital information down into > > DAPM and make everything a component). > > Thanks. > > ASRC M2M case needs to run as fast as possible, no sync clock control. > If use sound card to handle ASRC M2M case, the user application > should be aplay/arecord, then we need to consider xrun issue, buffer > may timeout, sync between aplay and arecord, these should't be > considered by pure memory to memory operation. > > DPCM may achitect all the audio things in components and sound > card, it is good. but for the M2M case, it is complcated. not sure > it is doable. > Beside the concern in previous mail, DPCM needs to separate ASRC to be two substreams (playback and capture). But the ASRC needs the sample rate & format of input and output first then start conversion. If the playback controls the rate & format of input, capture substream controls the rate & format of output, as a result one substream needs to get information(dma buffer address, size... rate, format) from another substream, then start both substreams in the last substream. How to synchronize these two substreams is a problem. One stream can be released but another stream doesn't know . So I don't think it is a good idea to use DPCM for pure M2M case. So can I persuade you to consider the V4L2 solution? Best regards Wang Shengjiu
