音频框架结构

最新推荐文章于 2025-06-25 22:59:23 发布

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#框架 #codec #struct #android #user

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本文主要探讨了Android audiosubsystem Framework、OSS Framework以及ALSA Framework。在OSS Framework中，音频数据流主要包括while循环的持续写入、schedule等待DMA中断以及copy_from_user的数据拷贝。而ALSA Framework则借助底层驱动回调来管理流控制，并处理动态电源管理和消除爆音等问题。

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1.2.1 Android audiosubsystem Framework

1.2.2 OSS Framework

Typical OSS Read/Write Flow

音频数据流原理相通，可以总结为三步骤：

while循环，持续写

schedule等待DMA中断产生

copy_frome_user拷贝数据到DMA缓存区

1.2.3 ALSA Framework

Not like OSS,ALSA sound core will manage flow control with the help of low level drivercallbacks.

static int soc_pcm_prepare(struct snd_pcm_substream *substream)
{
        if (machine->ops && machine->ops->prepare) {
                ret = machine->ops->prepare(substream);
        }   

        if (platform->pcm_ops->prepare) {
                ret = platform->pcm_ops->prepare(substream);
        }   

        if (codec_dai->ops->prepare) {
                ret = codec_dai->ops->prepare(substream, codec_dai);
        }   

        if (cpu_dai->ops->prepare) {
                ret = cpu_dai->ops->prepare(substream, cpu_dai);
        }   
        ... 
}

Except that, maintain issues likedynamic power management , pops elimination and so on with the help of lowlevel driver callbacks.(在底层驱动有例子)

static struct snd_pcm_ops soc_pcm_ops = {
	.open		= soc_pcm_open,
	.close		= soc_codec_close,
	.hw_params	= soc_pcm_hw_params,
	.hw_free	= soc_pcm_hw_free,
	.prepare	= soc_pcm_prepare,
	.trigger	= soc_pcm_trigger,
};