Linux Driver: Audio driver (i) alsa__linux

First, "Basic knowledge"

1, J2 "--hpr_out+hpl_out"--U13 (TLV320AIC3104IRHBR) hprout+hplout

2. Driving source code

Ipnc_rdk_v3.8.0.1/source/ti_tools/ipnc_psp_arago/kernel/sound/soc/codecs/tlv320aic3x.c

3, depends on the I2C drive

4, sound card driver frame: ALSA (Advanced Linux Sound architecture)

5, ALSA website: http://www.alsa-project.org

6, the structure body Snd_card describes a sound card device

7, the structure body snd_device the description child equipment

8, sound card equipment

Lisa@ubuntu:kernel$ls/dev/snd/-L

Total dosage 0

Drwxr-xr-x 2 root 815 09:10 By-Path

CRW-RW---t+1 root audio 116, 275 09:10 controlC0

CRW-RW---t+1 root audio 116, 235 09:10 midic0d0

CRW-RW---t+1 root audio 116, 265 09:11 pcmc0d0c

CRW-RW---t+1 root audio 116, 255 09:36 pcmc0d0p

CRW-RW---t+1 root audio 116, 245 09:10 pcmc0d1p

CRW-RW---t+1 root audio 116, 225 09:10 seq

CRW-RW---t+1 root audio 116, 545 09:10 Timer

lisa@ubuntu:kernel$ls/dev/snd/by-path/-L

Total dosage 0

lrwxrwxrwx1 root root 335 09:10pci-0000:02:03.0->. /controlc0

9. Main equipment Number

In Include/sound/core.h

#defineCONFIG_SND_MAJOR 116/* standardconfiguration * *

10, Sound Directory Description: In the "depth of practice embedded ..." "640 pages

Second, "Driving framework"

1. Create sound card: Snd_card_new (Linux 2.6.22 snd_card_create replaced)--->

2, the creation of child devices:

Snd_device_new (Snd_pcm_new, Snd_rawmidi_new, Snd_ctl_new, Snd_timer_new, snd_card_proc_new, snd_jack_new)--->

3, registered sound card: snd_card_register

Third, "PCM function"

PCM: Pulse-coded modulation, converting analog to digital

0, the structure of the inclusion of relations

0.1struct snd_pcm--> snc_pcm_str--> snd_pcm_substream--> (snd_pcm_ops+ snd_pcm_runtime)

0.2snd_pcm_runtime--> Snd_pcm_hardware

1. Structure Description Pcm:struct SND_PCM

2, Registered Pcm:snd_pcm_new

3. PCM Stream and PCM stream: Snc_pcm_str, Snd_pcm_substream

4. Important structural body in sub-flow

4.1snd_pcm_ops: The operation method of PCM flow need to be implemented in the specific sound card

4.2snd_pcm_runtime: Hardware descriptions, interrupt callbacks, DMA buffers, and private data need to be implemented in a specific sound card

4.2.1snd_pcm_hardware: Hardware Description

5, the establishment of PCM equipment files

5.1 Structural body describing logical devices: Snd_minor

5.2 Establishment Process:

snd_card_register--> snd_pcm_register-->snd_pcm_new--> snd_pcm_dev_register--> For_dev--> (Snd_kernel_minor get device number +device_create create device node)

6, the PCM equipment file access

6.1 Designation of the file Operation F_ops

An action set is an item in a snd_pcm_f_ops array, defined in SOUND/CORE/PCM_NATIVE.C

6.2 Registering character devices

Alsa_sound_init--> Register_chrdev (Major, "Alsa", &snd_fops)

There is only one snd_open function in the Snd_fops, which takes the corresponding Snd_minor object from the snd_miors array and replaces the action set (FILE->F_OP) of the file with the F_ops member of the object, based on the secondary device number. Specific to PCM device (a Snd_minor object), the file operation set is the corresponding operation in Snd_pcm_f_ops

Four, "sound card Control"

1. Control Item Creation

1.1 Description Control Structure body: Snd_kcontorl (include/sound/control.h)

1.2 Creating the control function: Snd_ctl_new1

1.3 Add the control to the sound card to which it belongs: Snd_ctl_add

1.4 Control callback Function: info, GET, put

2, Cotrol Equipment establishment

snd_card_create--> snd_ctl_new--> Snd_ctl_dev_register-->snd_register_device_for_dev--> (snd_kernel_ Minor Get device number +device_create create device node)

3, Cotrol equipment file access

Process is the same as PCM, different points: replace the set of file operations into Snd_ctl_f_ops