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I am struggling to find some area of code in the kernel that gets executed while audio is playing. My current goal is to be able to find the actual ...
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- 03-27-2013 #1
- Join Date
- Mar 2013
Sound / Audio Entry Point
I am struggling to find some area of code in the kernel that gets executed while audio is playing. My current goal is to be able to find the actual audio data in the kernel and print some of it out to make sure I can actually see audio bytes going through the kernel. Do you know of anywhere in the code that I could insert a printk() and see some data? If not, do you know of any entry point in the kernel sound code that gets executed every time audio gets played?
I would appreciate information about any version of the kernel that you are familiar with, but I am currently using version 18.104.22.168.
I have tried putting printk()s in sound/core/pcm_lib.c in functions like snd_pcm_lib_write_transfer. When playing audio, none of those messages show up, so I'm not really sure where else to look at this point.
Any help is greatly appreciated.
- 03-27-2013 #2
- Join Date
- Mar 2009
I'd start by reading a bit at alsa-project
As a quick tip, since you are not writing a _new_ PCI driver yourself, you can skip directly to the PCM-part (which is raw, uncompressed sound that is passed to the sound card).
Try writing a short client yourself, and I say this for several reasons:
- you have absolute control over the client part (mplayer and friends does a _lot_ of magic stuff)
- you can fine-tune the framesizes
- you will learn how sound is being fed through both the userspace-library and into the kernel