linux音频alsa-uda134x驱动文档阅读.pdf

前言

目前，linux系统常用的音频驱动有两种形式:alsa oss

alsa:现在是linux下音频驱动的主要形式，与简单的oss兼容。

oss：过去的形式

而我们板子上的uda1341用的就是alsa驱动。

alsa概述：

因为我们用的是板上系统，用的也是alsa 的一个soc子系统。所以我们直接讲解alsa soc子系统。

subsystem there was some support in the kernel for SoC audio, however it

had some limitations:-

ALSA板上系统(ASoC)层的总体项目目标，是为对SOC嵌入式处理器和便携音频解码器提供更好的ALSA支持。在ASoC子系统之前，己有对内核的SoC音频支持，但是那些支持存在一些局限：

Codec drivers were often tightly coupled to the underlying SoC

CPU. This is not ideal and leads to code duplication - for example,

Linux had different wm8731 drivers for 4 different SoC platforms.

解码器常常与底层嵌入式处理器一对一紧密结合。这是非理想化的，因为这将导致代码的重复－例如，对四个不同的嵌入式平台，Linux要有不同的wm8731驱动。（理想的状态是我们可以只有一个wm8731的驱动代码，就可以对应于四个不同的处理器，但由上面说的，解码器－这里的wm8731与底层嵌入式处理器结合过于紧密，无法实现wm8731驱动代码的复用）

* There was no standard method to signal user initiated audio events (e.g.

Headphone/Mic insertion, Headphone/Mic detection after an insertion

event). These are quite common events on portable devices and often require

power via changing codec oversampling rates, bias currents, etc.

放音（录音）时，驱动常常会打开整个解码器。对个人电脑来说这没什么问题，但是在便携设备上往往会导致电能的浪费。另外，也没有通过改变解码器采样率、偏置电流等方式来省电的支持。

ASoC Design

ASoC 设计

===========

The ASoC layer is designed to address these issues and provide the following

features :-

ASoC层被设计用来解决这些问题并提供如下特性：

* Codec independence. Allows reuse of codec drivers on other platforms

and machines.

* Dynamic Audio Power Management (DAPM). DAPM automatically sets the codec to

its minimum power state at all times. This includes powering up/down

internal power blocks depending on the internal codec audio routing and any

active streams.

动态音频电源管理（DAPM）。DAPM自动无论何时，总是把解码器自动设置为它的最小电源状态。这包括依据内部解码音频线路和活跃的流来开启和关闭内部电源模块

* Pop and click reduction. Pops and clicks can be reduced by powering the

codec up/down in the correct sequence (including using digital mute). ASoC

signals the codec when to change power states.

咔嗒声减少。咔嗒声可以通过使用正确的解码器电源开启和关闭顺序而减少（包括使用数字消音）。ASoC在改变电源状态时向解码器发出信号。

* Machine specific controls: Allow machines to add controls to the sound card

controls, audio interface capabilities, codec DAPM definition and codec IO

functions.

解码器驱动：解码器驱动是平台无关的，包含音频控制、音频接口能力、解码器动态音频电源管理和解码器IO函数。

* Platform driver: The platform driver contains the audio DMA engine and audio

interface drivers (e.g. I2S, AC97, PCM) for that platform.

平台驱动：平台驱动包含相应平台的音频DAM引擎和音频接口驱动(如I2S,AC97,PCM)

* Machine driver: The machine driver handles any machine specific controls and

audio events (e.g. turning on an amp at start of playback).

机器驱动：机器驱动处理所有机器相关的控制和音频事件（如回放开始时打开放大器）。

Documentation

overview.txt:概述，本文件。

codec.txt: Codec driver internals.

codec.txt:解码器驱动内部实现

DAI.txt: Description of Digital Audio Interface standards and how to configure

a DAI within your codec and CPU DAI drivers.

DAI.txt:对数字音频接口（DAI）标准和如何配置你的解码器和CPU的数字音频接品驱动中的数字音频接口的描述。

dapm.txt: Dynamic Audio Power Management

dapm.txt:动态音频电源管理

platform.txt: Platform audio DMA and DAI.

platform.txt:平台音频DMA和DAI。

linux音频alsa-uda134x驱动文档阅读之二（时钟)

已有 922 次阅读 2009-11-23 10:31 |个人分类:音频驱动|关键词:文档 时钟 音频 linux 驱动

Audio Clocking

音频时钟

==============

This text describes the audio clocking terms in ASoC and digital audio in

general. Note: Audio clocking can be complex!

本文本总体描述ASoC和数字音频中的音频时钟条款。

Master Clock

主时钟

Some master clocks (e.g. PLLs and CPU based clocks) are configurable in that

their speed can be altered by software (depending on the system use and to save

power). Other master clocks are fixed at a set frequency (i.e. crystals).

有些主时钟是可配置的（如基于锁相环或处理器的时钟），它们可以通过软件改变速度（依赖于系统应用和省电的考虑）。另一些主时钟则是固定于一个特定的频率值（如晶振）。

DAI Clocks

数字音频时钟

----------

The Digital Audio Interface is usually driven by a Bit Clock (often referred to

as BCLK). This clock is used to drive the digital audio data across the link

between the codec and CPU.

位时钟可以有如下产生方式：

BCLK = MCLK / x

or

BCLK = LRC * x

or

BCLK = LRC * Channels * Word Size

This relationship depends on the codec or SoC CPU in particular. In general

it is best to configure BCLK to the lowest possible speed (depending on your

rate, number of channels and word size) to save on power.

这个关系依赖于解码器，特别是板上处理器。大体上讲，最好将位时钟尽可能低速（取决于你的采样率，通道数和字长）以省电。

ASoC解码器驱动

=================

The codec driver is generic and hardware independent code that configures the

codec to provide audio capture and playback. It should contain no code that is

specific to the target platform or machine. All platform and machine specific

code should be added to the platform and machine drivers respectively.

解码器驱动是通用、硬件无关的代码，它配置解码器以支持音频捕获与回放。它不应包含任何与目标平台或机器相关的代码。平台或机器相关代码应该分别加 入到平台和机器驱动中去。

Each codec driver *must* provide the following features:-

各解码器驱动必须提供如下特性：

1) Codec DAI and PCM configuration