At Wed, 18 Apr 2007 07:14:42 -0700 (PDT), Ciaccia wrote:
Takashi, I look through the code, I found some interesting examples...
Instead of defining a 2 as a min number of channel, could I use the following code?
static int ep93xx_ioctl(struct snd_pcm_substream *substream, unsigned int cmd, void *arg) { if (cmd == SNDRV_PCM_IOCTL1_CHANNEL_INFO ) { struct snd_pcm_channel_info *info=arg; info->offset = 0; info->first = info->channel * 32; info->step = 64; return 0; }
return snd_pcm_lib_ioctl(substream, cmd, arg);}
Would that work? Or should I always support stereo even when not needed?
Yes, this would work. But, I'm not sure whether all apps work well with this setting because this feature is used by only few drivers. So, I recommend first try to use the stereo only, then try this after that.
Takashi
Ciao Andrea
--- Takashi Iwai tiwai@suse.de wrote:
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
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