[linux-audio-user] how enabling non-audio (AC3, DTS, MP3) S/PDIF out at ALSA?

franciscojfraga at gmail.com (Francisco Fraga) · Wed Dec 7 06:10:29 2005

Hi everybody,

  I would like to know how I could enable  the use of non-audio (AC3,
DTS, MP3) S/PDIF out at the ALSA context, in a set-top-box with the
ALC650 AC'97 chipset, without having to re-compile the Linux kernel.

 In the linux-2.6.13 kernel, in line 1733 of the the source code
"sound/pci/ac97/ac97_patch.c", there is a function:
"patch_alc650(ac97_t * ac97)". In this funcion, several ALC650
registers are read and written. I know that, for enabling non-audio
(AC3, DTS, MP3) S/PDIF out in an AC'97 chipset, I have to put a "1" at
the 2nd LSB bit of the MX3A register, and also choose the correct
Category Code for the non-audio S/PDIF format (AC3, DTS or MP3).

 So I have to basic problems to solve:

  1. Find out how to create an AC'97 instance (ac97_t * ac97), in
order to use the function  "void snd_ac97_write_cache(ac97_t *ac97,
unsigned short reg, unsigned short value)" for writing in the MX3A
register;

  2. Find out  the correct Category Code for each non-audio S/PDIF
format (AC3, DTS or MP3).

  If someone could help me, I would be very grateful.

           Best,

                Francisco