1 =======================
2 ALSA SoC Layer Overview
3 =======================
4
5 The overall project goal of the ALSA System on
6 provide better ALSA support for embedded syste
7 pxa2xx, au1x00, iMX, etc) and portable audio c
8 subsystem there was some support in the kernel
9 had some limitations:-
10
11 * Codec drivers were often tightly coupled t
12 CPU. This is not ideal and leads to code d
13 Linux had different wm8731 drivers for 4 d
14
15 * There was no standard method to signal use
16 Headphone/Mic insertion, Headphone/Mic det
17 event). These are quite common events on p
18 machine specific code to re-route audio, e
19 event.
20
21 * Drivers tended to power up the entire code
22 recording) audio. This is fine for a PC, b
23 power on portable devices. There was also
24 power via changing codec oversampling rate
25
26
27 ASoC Design
28 ===========
29
30 The ASoC layer is designed to address these is
31 features :-
32
33 * Codec independence. Allows reuse of codec
34 and machines.
35
36 * Easy I2S/PCM audio interface setup between
37 interface and codec registers its audio in
38 core and are subsequently matched and conf
39 hardware parameters are known.
40
41 * Dynamic Audio Power Management (DAPM). DAP
42 its minimum power state at all times. This
43 internal power blocks depending on the int
44 active streams.
45
46 * Pop and click reduction. Pops and clicks c
47 codec up/down in the correct sequence (inc
48 signals the codec when to change power sta
49
50 * Machine specific controls: Allow machines
51 (e.g. volume control for speaker amplifier
52
53 To achieve all this, ASoC basically splits an
54 multiple re-usable component drivers :-
55
56 * Codec class drivers: The codec class drive
57 contains audio controls, audio interface c
58 definition and codec IO functions. This cl
59 ICs if required. Codec class drivers shoul
60 on any architecture and machine.
61
62 * Platform class drivers: The platform class
63 engine driver, digital audio interface (DA
64 and any audio DSP drivers for that platfor
65
66 * Machine class driver: The machine driver c
67 describes and binds the other component dr
68 "sound card device". It handles any machin
69 machine level audio events (e.g. turning o
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