ALSA tvmixer

ALSA snd-tvmixer

 Name                    Last modified      Size  Description
 Parent Directory                             -   
 i2c-compat.h            12-Jun-2005 14:01  1.0K  
 tvmixer-2615-2616.patch 10-May-2006 13:43  943   
 tvmixer.102c.c          12-Jun-2005 14:01   12K  
 tvmixer.102c.patch      12-Jun-2005 14:01  3.0K  
 tvmixer.104.c           12-Jun-2005 14:01   13K  
 tvmixer.104.patch       12-Jun-2005 14:01  801   
 tvmixer.26x.c           12-Jun-2005 14:01   14K  
 tvmixer.26x.patch       12-Jun-2005 14:01  1.0K  
 tvmixer.cvs.c           12-Jun-2005 14:01   14K  
 tvmixer.dif             12-Jun-2005 14:01   17K  
 tvmixer.no_magic.diff   12-Jun-2005 14:01  1.3K  
 tvmixer2615.patch.bz2   09-Mar-2006 15:37  4.2K

ALSA tvmixer When I was insipred to try out the ALSA snd drivers, I was faced with an incomplete migration, due to the lack of an ALSA tvmixer mixer device. I've cobled together what I think is a fully functional snd-tvmixer, with volume, bass and treble.

To get this far, I took Gerd Knorr's tvmixer, and spliced in the ALSA functions needed to create the 'chip,' 'card' and 'ctrl' structures that the snd core uses, and created the functions that the 'ctrl' structures refer to.

This is all based on Takashi Iwai's Writing an ALSA Driver document.

I'll be refering to other documents at the ALSA 0.9.x Developer documentation page as I work on more features.

AlsaOpensrcOrg has good information on setting up ALSA on your system on the Quick Install page.

I have patches against several kernel releases. It is a moving target, so your mileage may vary.

I now have support for the 1.0.2c and 1.0.4 releases of alsa-driver to be used with the 2.4 kernels, and the 2.6 kernel which has ALSA in it already. Things are a little different for each, so read carefully!

Adding snd-tvmixer to the kernel

The patches I've be prepared for the 2.6.10 and newer kernels can be found at the v3tv-v4l2 page. You do not need to do any thing here.

linux-2.6.16 kernel

First apply tvmixer2615.patch.bz2, then tvmixer-2615-2616.patch to catch up with the moving target.

Compile the kernel as usual. 'make oldconfig', 'make' and 'make modules_install' might be all that is needed.

linux-2.6.15 kernel

Apply tvmixer2615.patch.bz2

Compile the kernel as usual. 'make oldconfig', 'make' and 'make modules_install' might be all that is needed.

linux-2.6 kernel

Copy tvmixer.26x.c to linux-2.6.X /sound/drivers/tvmixer.c

With kernel releases 2.6.6 and earlier, only appy tvmixer.26x.patch to update Kconfig and Makefile in the linux/sound/drivers/ directory.

I have not prepared patches for kernels from 2.6.7 to 2.6.9. At some point the snd_magic_* stuff has been removed from ALSA. If you are keeping up with the latest, apply tvmixer.no_magic.diff.
Compile the kernel as usual. 'make oldconfig' and 'make' might be all that is needed. Now install the modules and bzImage, and reboot.

Adding snd-tvmixer to your local copy of cvs

alsa-driver-1.0.2c

Copy the tvmixer.102c.c file to alsa-driver-1.0.2c/i2c/tvmixer.c
Apply the patch tvmixer.102c.patch to add support for the tvmixer to the Makfile and Modules.dep files. (i2c-compat.h is in the patch)

alsa-driver-1.0.4

Copy the tvmixer.104.c file to alsa-driver-1.0.4/drivers/tvmixer.c
Copy the i2c-compat.h file to alsa-driver-1.0.4/drivers/i2c-compat.h
Apply the patch tvmixer.104.patch to add support for the tvmixer to the Makfile and Kconfig files.

ALSA: CVS repository

Follow the directions for Anonymous CVS Access, and checkout 'alsa-driver'

Apply the tvmixer.dif patch ( from alsa-driver's parent directory )

patch -p0 < tvmixer.dif

The first time you apply the patch, you run cvscompile (even if you're using a snapshot) not configure! Later, you can re-run configure to change options.

Run cvscompile, giving it any configure options you would use, and adding 'tvmixer' to the --with-cards option.

./cvscompile --with-cards=tvmixer, _your_card_here_

This will rebuild some of the config files, then pass your args to configure.

Now do make and install, and your almost there!

Configuring Modules

I've included notes on /etc/modules.conf in the old V3TV HOWTO for the 2.4 kernels, and with the notes for the 2.6 kernel.

The main issue is identifying what ALSA mixer control the OSS 'VOLUME' control is going to affect. The document Notes on Kernel OSS-Emulation has a few pointers on the 'echo' statement needed to get OSS apps to talk to the ALSA tvmixer.

Whats going on in [snd-]tvmixer.c?

We have the standard ALSA snd module paramaters, including 'index' which replaces 'iminor' for indicating the /dev/mixerN postion of the particular audio chip refrenced.

The TVMIXER struct is now snd_tvmixer. Each tvmixer is dynamically alocated by snd_device_new in snd_tvmixer_create. The array mixers[] holds a pointer to each tvmixer.

I think it would be good to have mixers as a linked list, then the 'slot' counter would not be needed.

The various snd_tvmixer_volume_xxx, snd_tvmixer_mute_xxx and snd_tvmixer_bass_treble_xxx handle the real work of changing mixer settings.

The snd_tvmixer_build function adds the mixer controls to the tvmixer->snd_card structure.

snd_tvmixer_dev_free is the snd_device call back to rlease the tvmixer memory allocation.

snd_tvmixer_create allocates a tvmixer struct with snd_magic_kcalloc.

The function snd_tvmixer_adapters evaluates each i2c adapter to see if it is a video capture card, and calls snd_tvmixer_clients for each client present.

In snd_tvmixer_clients, we first check to see if the i2c_client is already known, in which case it is freed.

If it is not known, then we check that mixers[] is not full. Then we need to see if the i2c_client has a command function. Next we try to get the audio chip's properties.

Now comes the ALSA specific setup. We get a snd_card with snd_card_new, and call snd_tvmixer_create to get a tvmixer allocated. After assigning a few name strings, the mixer controls are registered by snd_tvmixer_build.

Finally we see if it all works with a call to snd_card_register. On success we add the new tvmixer to mixers[], increment the cards counter, then print a happy message to the syslog.

The rest is the usual i2c module init and exit routines.

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