[alsa-devel] S24_LE Mode for USB Driver
tiwai at suse.de
Wed Aug 13 14:27:05 CEST 2008
At Wed, 13 Aug 2008 13:17:44 +0200,
Clemens Ladisch wrote:
> Takashi Iwai wrote:
> > Charles Eidsness wrote:
> > > It looks like the parse_audio_format_i_type function at line 2369 of usbaudio.c
> > > (linux v2.6.23) doesn't support the case where bSubframeSize (fmt) = 4 bytes
> > > and bBitResolution (fmt) = 24 bits, which should correspond to a S24_LE (or
> > > BE) type. I'm developing a new USD DAC which supports this mode (24-bit sample
> > > in a 4 byte package). Right now Linux sends me S32_LE formated data, which is
> > > wrong. Would it be possible to expand this function to support S24_LE/BE? It
> > > would only require adding a few lines of code.
> > Yes, it's possible, of course.
> > BTW, is this behavior strictly defined? I fail to find in the
> > usb-audio spec that bBitResolution specifies the lower bits, not the
> > higher bits...
> The spec assumes that 24-bit samples use S24_3LE. 24-bit samples in
> 32-bit words are an extension that must be handled with some device-
> specific code (like with the UA-1000).
> (The audio 2.0 spec allows 32-bit words, and the wording seems to imply
> that samples are aligned to the most significant bit, i.e., that S32_LE
> would be used in this case.)
OK, thanks for clarification.
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