1、Linux 音频架构图
音视频的好坏 直接影响 产品体验
2、音频架构图层次说明
openWRT 采用 ALSA 层次图,如下
Application: 上层应用 主要调用alsa-lib 中的接口 实现业务逻辑。使用alsa-util中aplay,arecord,amixer,speaker-test进行相关测试。
HAL层 : 移植alsa-lib 和 alsa-utils. 在openwrt中 feeds 自带了alsa-lib 1.1.01[简介]
kernel: 按照ALSA 驱动层进行适配。[简介]
3、Application层
openwrt中应用启动需要自定义启动脚本,放在目录/etc/init.d 目录下。
4、启动脚本顺序定义
05 defconfig //加载默认参数
10 boot //启动
39 usb // 加载usbfs
40 network // 设置网卡参数
45 firewall // 防火墙
50 dropbear // sshd server
50 cron // …
50 telnet // 如果没有修改root密码,则启动telnet server
60 dnsmasq // DHCP 和 DNS 服务端
95 done // …
96 led // 指示灯
97 watchdog // …
99 sysctl // 最后,进行必要的内核参数调整
5、启动脚本书写
按照官方Wiki脚本,进行自定制。
6、HAL层
这一层不需要做太多改动,需要配置feeds选择自己需要的版本即可,
具体的接口查询,可以到alsa-project查询。
7、kernel
根据ALSA驱动进行相关分析。
machine
/* SoC machine */
struct snd_soc_card {
char *name;
...
int (*probe)(struct platform_device *pdev);
int (*remove)(struct platform_device *pdev);
/* the pre and post PM functions are used to do any PM work before and
* after the codec and DAIs do any PM work. */
int (*suspend_pre)(struct platform_device *pdev, pm_message_t state);
int (*suspend_post)(struct platform_device *pdev, pm_message_t state);
int (*resume_pre)(struct platform_device *pdev);
int (*resume_post)(struct platform_device *pdev);
...
/* CPU <--> Codec DAI links */
struct snd_soc_dai_link *dai_link;
int num_links;
...
};
probe/remove 可选,主要侦测machine。
suspend/resume 在codec,DAIs和DMA suspend resume 会相应的触发,也是可选的
machine DAI口配置,配置对应的结构体
/* digital audio interface glue - connects codec <--> CPU */
static struct snd_soc_dai_link corgi_dai = {
.name = "WM8731",
.stream_name = "WM8731",
.cpu_dai_name = "pxa-is2-dai",
.codec_dai_name = "wm8731-hifi",
.platform_name = "pxa-pcm-audio",
.codec_name = "wm8713-codec.0-001a",
.init = corgi_wm8731_init,
.ops = &corgi_ops,
};
/* audio machine driver */
static struct snd_soc_card snd_soc_corgi = {
.name = "Corgi",
.dai_link = &corgi_dai,
.num_links = 1,
};
plarform
DMA 驱动,Soc DAI 驱动
/* SoC audio ops */
struct snd_soc_ops {
int (*startup)(struct snd_pcm_substream *);
void (*shutdown)(struct snd_pcm_substream *);
int (*hw_params)(struct snd_pcm_substream *, struct snd_pcm_hw_params *); int (*hw_free)(struct snd_pcm_substream *);
int (*prepare)(struct snd_pcm_substream *);
int (*trigger)(struct snd_pcm_substream *, int);
};
//平台驱动通过DMA接口关联起来
struct snd_soc_platform_driver {
char *name;
int (*probe)(struct platform_device *pdev);
int (*remove)(struct platform_device *pdev);
int (*suspend)(struct platform_device *pdev, struct snd_soc_cpu_dai *cpu_dai);
int (*resume)(struct platform_device *pdev, struct snd_soc_cpu_dai *cpu_dai);
/* pcm creation and destruction */
int (*pcm_new)(struct snd_card *, struct snd_soc_codec_dai *, struct snd_pcm *);
void (*pcm_free)(struct snd_pcm *);
/*
* For platform caused delay reporting.
* Optional.
*/
snd_pcm_sframes_t (*delay)(struct snd_pcm_substream *, struct snd_soc_dai *);
/* platform stream ops */
struct snd_pcm_ops *pcm_ops;
};
codec
每个codec codec 驱动必须具备以下功能
codec DAI 与 PCM 配置
使用I2C 或者SPI控制IO
mixer audio 控制
codec 音频操作
DAPM 描述
DAPM 事件处理
可选
DAC mute处理
// DAI PCM配置
static struct snd_soc_dai_ops wm8731_dai_ops = {
.prepare = wm8731_pcm_prepare,
.hw_params = wm8731_hw_params,
.shutdown = wm8731_shutdown,
.digital_mute = wm8731_mute,
.set_sysclk = wm8731_set_dai_sysclk,
.set_fmt = wm8731_set_dai_fmt,
};
struct snd_soc_dai_driver wm8731_dai = { .name = "wm8731-hifi",
.playback = { .stream_name = "Playback",
.channels_min = 1,
.channels_max = 2,
.rates = WM8731_RATES,
.formats = WM8731_FORMATS,
},
.capture = { .stream_name = "Capture",
.channels_min = 1,
.channels_max = 2,
.rates = WM8731_RATES,
.formats = WM8731_FORMATS,}, .ops = &wm8731_dai_ops,
.symmetric_rates = 1,
};
// i2c 控制 读写
i2c_write
i2c_read
// mixer audio control
codec 说有mixer与control都定义在soc.h中
#define SOC_SINGLE(xname, reg, shift, mask, invert)
定义单一控制器:-
xname 控制名称e.g. “Playback Volume”
reg = codec register
shift = control bit(s) offset in register
mask = control bit size(s) e.g. mask of 7 = 3 bits
invert = the control is inverted 是否反转
其他宏包括: –
#define SOC_DOUBLE (xname ,reg ,shift_left ,shift_right ,mask ,invert )
立体声控制
#define SOC_DOUBLE_R (xname ,reg_left ,reg_right ,shift ,mask ,invert )
一个跨越2个寄存器的立体声控制
#define SOC_ENUM_SINGLE (xreg ,xshift ,xmask ,xtexts )
xreg = 寄存器
XSHIFT = 控制位(小号)偏移在寄存器
xmask = 控制位(小号)大小
xtexts = 指向描述每个设置的字符串数组的指针
//audio 控制操作
/* SoC audio ops */
struct snd_soc_ops {
int (*startup)(struct snd_pcm_substream *);
void (*shutdown)(struct snd_pcm_substream *);
int (*hw_params)(struct snd_pcm_substream *, struct snd_pcm_hw_params *); int (*hw_free (struct snd_pcm_substream *);
int (*prepare)(struct snd_pcm_substream *);
};
//DAPM
//DAPM handler 参考
8、openWRT 音频应用
上面一节介绍了音频框架。在openWRT音频业务主要VOIP通过 ,上/下行通过模块如下:
9、调试技术
链路上应用层UDP截取文件
知道UDP 下的G711A 对应的buffer
// 应用层将buffer写到文件 代码块
static struct file *file_g711a= NULL;
int writelen = 0;
if (NULL == fp)
{
file_g711a= file_open("/test1", O_RDWR | O_CREAT, 0777);
if(file_g711a == NULL){
printf("g711a file = NULL");
}else{
printf("g711a file open ok");
}
}
if(file_g711a != NULL){
writelen = fwrite(g711a_buffer, 1, sizeof(g711a_buffer), file_g711a);
}
printk("writelen:%dn",writelen);
10、链路上 alsa 截取文件
转换成PCM后,将对应的buffer 写道文件
// 应用层将buffer写到文件 代码块
static struct file *file_pcm= NULL;
int writelen = 0;
if (NULL == fp)
{
file_pcm= file_open("/test.pcm", O_RDWR | O_CREAT, 0777);
if(file_pcm == NULL){
printf("pcm file = NULL");
}else{
printf("pcm file open ok");
}
}
if(file_pcm != NULL){
writelen = fwrite(pcm_buffer, 1, sizeof(pcm_buffer), file_pcm);
}
printk("writelen:%dn",writelen);
链路上kernel 截取文件
在PCM与DMA通信的函数中 将buffer 写到文件中
// kernel 将buffer写到文件 代码块
static struct file *fp = NULL;
mm_segment_t fs;
static loff_t pos = 0;
printk("hello entern");
if (NULL == fp)
{
fp = filp_open("/test.pcm", O_RDWR | O_CREAT, 0777);
if (IS_ERR(fp))
{
printk("create file errorn");
return -1;
}
}
fs = get_fs();
set_fs(KERNEL_DS);
int writelen = vfs_write(fp, buf, size*4, &pos);
pos += size*4;
printk("writelen:%d pos:%dn",writelen, pos);
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