[alsa-devel] Access to bytes from the raw audio stream? (AC'97)

John Graham johngavingraham at googlemail.com
Wed Feb 3 17:27:05 CET 2010

> With a lot of AC97 controllers the hardware won't allow you direct
> access to the cooked wire data, you'll only be able to see decoded audio
> streams.  What is it that you're actually trying to do?

Basically, we've got a problem where we think our processor is
bit-shifting the sample for some reason, and I was going to see if I
could either (i) un-bit-shift it (it looks like we're not actually
losing any data, the sound's just being multiplied by 2^4), or (ii)
reproduce the problem we see by bit-shifting the samples on a
known-good platform.

> For embedded platforms you mostly want to look under sound/soc though
> there are a few platforms outside of there.

I know the drivers for our particular setup (UBC1400 codec/i.MX25
processor) are under sound/arm, but I'm not sure if there's anything
in there that actually sees the samples as they come through.

Would I be able to access samples quite early on in the generic AC'97
code (I don't know where that is, either, but it would be interesting
to see, at least :p)


John G

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