Hi,

For a while now, I have been going around asking this question, yet fellow Linux-users seem to shy away from it, which is causing me to be somewhat alarmed.

Im trying to write a library/module to allow another user-space app to access the audio codec (sound chip) using the AC 97' interface. I have looked at the Linux sound driver code (ac97.h, ac97.c and ac97_codec.c) and the Intel documentation, and I still cant figure out how the 'actual' controlling the sound chip is done. The FreeBSD book was the closest thing I got to having my questions answered. I run Slackware (10.2 and 11), Debian 3.1 sarge and FreeBSD 6.2 on my machines.

Lemme see if I can summarize my questions:

1) What is the lowest module that does the actual communication with the AC97 interface in that linux driver?
2) Whats the method used to do the communication? Device I/O thru ports, DMA, etc.?

What Im looking for really, is a general description of the process starting with being passed a pointer to the audio data buffer and ending with sending that data to the AC97 to be played.

Best
Pete

ac97.c and the other files are the right ones. If you search closely, there's register reading/writing there. And that's how AC97 chips are controlled. You can view documentation of an example chip, like the one you can download from http://www.analog.com/en/prod/0,2877,AD1881A,00.html