At Tue, 17 Apr 2007 04:36:28 -0700 (PDT), Ciaccia wrote: > > Hi Takashi, > Thanks for your explanation. My request was not clear, > since my understanding of ALSA is lacking and I need > to understand more... > > The driver I currently have is here: > http://www.pecore.ch/test/ep93xx-i2s.c.txt > > It's really messy, it performs all the format > conversions in the driver (they could be done in the > alsa-lib) and it lacks some functionalities, so I > would like to make it shorter, better and more > readable. > > The driver does not currently define > SNDRV_PCM_INFO_MMAP and the memory is copied in the > copy callback. I would like to delete the copy > callback (which is not really used), since the samples > could be written directly to the dma buffer by > alsa-lib. > > How does alsa-lib know how to store the samples in the > dma-buffer? Based on the information the driver gives: access, formats, channels, etc. > How does alsa-lib know that the samples > are interleaved, access has SNDRV_PCM_ACCESS_{MMAP|RW}_INTERLEAVED. > occupy 32 bits each one (even if the > format is 24 bits) and that the left channel samples > are at index #0 and the left ones at index #1? formats has SNDRV_PCM_FMTBIT_S16_{LE|BE}. > Or that > between two consecutive samples in mono there should > be a 4 bytes gap? It's possible to support a non-standard stream like that, but it's a bit complicated. So, I recommend not to support this first (i.e. channels_max = channels_min = 2). Then alsa-lib will copy the mono stream automatically to stereo. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
