Rockchip USB Gadget UAC：音频配置、测试与完整设备描述符

ArmSoM 平台参考，来源为中文 RK-KF-YF-098 V1.3.1。原稿覆盖全部 Rockchip 芯片（MCU 除外）、Linux 4.4 及以上；不等于所有 ArmSoM 板卡均已适配。须核对具体板卡、SoC、SDK/BSP、内核补丁、USB 接口与 codec。全部日志和测试为原稿示例，本次未进行硬件验证。仅有中文 PDF，四语均使用中文原图。

原稿疑点保留：Full/High Speed 写为 12/480 MHz；176 kHz 对应 1056 bytes；60×24×96 kHz 写为132 Mbit/s；SOF 周期写为128us。上述单位/算式存在疑点，未替换原值。Kernel-5.10 音量段落写 uvc_app，其余写 uac_app；Windows UAC2 Feature Unit 限制与较新内核默认音量配置应按实际 BSP 核实。示例包含删除 configfs 链接与切换 USB 功能，可能中断 ADB；未执行。

原稿技术前言：UAC1/UAC2 均支持基本录音和放音；UAC1 Legacy 需要实际声卡且仅支持放音；Audio Source 仅支持录音，但提供15种采样率。按产品需求选择。设备物理按键调节音量/静音需要额外 HID 控制，原稿发布的 SDK 尚不支持。开发参考：

Kernel/Documentation/usb/gadget-testing.txt — 6. HID function

Kernel/Documentation/ABI/testing/configfs-usb-gadget-hid

Universal Serial Bus Audio Device Class Specification for Basic Audio Devices — 8 HID Support in Basic Audio Devices

ArmSoM Docs · Rockchip Linux

1. 内核 UAC 配置

1.1 相关内核提交

Kernel-5.10 的 UAC1/UAC2 内核代码须更新到如下提交点后才能支持完整功能。

usb: gadget: u_audio: add uevent for ppm compensation

如果要正常使用 Kernel-4.4/4.19 的 UAC1/UAC2 的功能,需要先确认所使用的内核已经包含如下的系列补丁,如果未找到补丁,请提交问题到 Rockchip Redmine 平台,或者发邮件给本文档的作者。补丁列表:

usb: gadget: f_uac1: set baInterfaceNr of ac_header_desc dynamically
usb: gadget: u_audio: fix dev_dbg information
usb: gadget: f_uac: fix volume control to uevent
usb: gadget: u_audio: disable eps when usb disconnect
usb: gadget: u_audio: add uevent for ppm compensation
usb: gadget: f_uac: update maxpacket in function bind
usb: gadget: f_uac: add pktsize calculating at setting playback srate
usb: gadget: f_uac: add volume and mute feature unit
UPSTREAM: usb: gadget: f_uac2: fix packet size calculation
usb: gadget: u_audio: fix the risk of strcpy out of bounds
usb: gadget: f_uac1: disable IN/OUT ep if unused
usb: gadget: u_audio: add uevent for set_alt and set_srate
FROMLIST: usb: gadget: f_uac*: Support multiple sampling rates
FROMLIST: usb: gadget: f_uac*: Reduce code duplication
FROMLIST: usb: gadget: f_uac1: Fix endpoint reading

1.2 相关配置

CONFIG_USB_CONFIGFS_F_UAC1 (enable UAC1 Function )CONFIG_USB_CONFIGFS_F_UAC2 (enable UAC2 Function )CONFIG_USB_CONFIGFS_F_UAC1_LEGACY (enable UAC1 Legacy Function )CONFIG_USB_CONFIGFS_F_ACC (Audio Source depends on it)CONFIG_USB_CONFIGFS_F_AUDIO_SRC (enable Audio Source Function)

1.3 相关文档

Documentation/usb/gadget_configfs.txtDocumentation/usb/gadget-testing.txtDocumentation/ABI/testing/configfs-usb-gadget-uac1Documentation/ABI/testing/configfs-usb-gadget-uac1_legacyDocumentation/ABI/testing/configfs-usb-gadget-uac2

1.4 支持列表

表 1-1 Rockchip 平台 UAC1/UAC2 Device 支持的功能

Function	Uevent 控制	多采样率	多声道	Feature Unit 音量控制	时钟同步
UAC1	YES	YES	YES	YES	YES
UAC2	YES	YES	YES	YES	YES

Note:[1] Uevent 控制是指内核通过uevent 发送打开/关闭UAC,采样率设置,以及音量调节等事件给应用层uac_app,以达到控制声卡的目的,详⻅章节Uevent。[2] UAC2 的 Feature Unit 音量控制在 Windows 平台无法兼容。因此,建议 UAC1 启用Feature Unit 音量控制,UAC2关闭Feature Unit 音量控制。使用方法参考章节UAC Usage。[3] 时钟同步功能,是指通过动态调整音频时钟频率,使USB 主机时钟和USB 音频设备的时钟同步。当前SDK 只有RV1126-Linux-4.19 支持时钟同步。使用方法参考章节PPM Compensation。

2. UAC1/UAC2 使用与测试

2.1 UAC1 信息

USB Audio Class 1 standard (1998)This standard allows for 24 bits/96 kHz max.The standard itself doesn’t impose any limitation on sample rate.Class 1 is tied to USB 1 Full Speed = 12 MHzEvery millisecond a package is send.Maximum package size is 1023 bytes.2 channel x 24 bit x 96000 Hz sample rate= 4608000 bits/s or 576 Byte/msThis fits in the 1023 byte limit.

Any higher popular sample rate e.g. 176 kHz needs 1056 bytes so in excess of the maximumpackage size.All operating systems (Win, OSX, and Linux) support USB Audio Class 1 natively.This means you don’t need to install drivers, it is plug&play.All support 2 channel audio with 24 bit words and 96 kHz sample rateRockchip 平台 UAC1 驱动支持 USB Audio Class specification 1.0,支持录音和放音,并且不需要实际的声卡。UAC1 驱动设置 bInterval=4。默认支持:速率:High Speed采样率:playback 和 capture 都为 48 KHz声道数:playback 和 capture 都为 2 Channels位深度:playback 和 capture 都为 16 bitsNote:[1] USB Audio 1.0 Specification 在USB 2.0 core Specification 之前完成,因此USB Audio 1.0 Specification 没有高速模式(High Speed)这一概念。可以通过一些经验规则使得Audio 1.0 兼容设备在特定的操作系统上实现高速模式。比如修改isochronous endpoint descriptor 的bInterval=4,目前测试可以在各种平台上支持UAC1 的高速模式。在不同的Windows 系统版本上,而且兼容性更胜UAC2。[2] 采样率,声道数,位深度都可以通过内核提供的接口配置,详细使用说明请查看UAC Usage。

2.2 UAC2 信息

USB Audio Class 2 standard (2009)USB Audio Class 2 additionally supports 32 bit and all common sample rates > 96 kHzClass 2 uses High Speed (480 MHz). This requires USB 2 or 3.As the data rate of High Speed is 40 X Full speed, recording a 60 channel using 24 bits at 96 kHz (132Mbit/s) is not a problem.Using High Speed USB for playback there are no limits in resolution.It is downwards compatible with class 1.From mid-2010 on USB audio class 2 drivers are available in OSX 10.6.4 and Linux.Both support sample rates up to 384 kHz.Microsoft simply didn’t support UAC2.In April 2017, an update of Win10 finally brought native mode drivers.If you use older versions of Win, you still need a third party driver.Rockchip 平台 UAC2 驱动支持 USB Audio Class specification 2.0,支持录音和放音,并且不需要实际的声卡。默认支持:速率:High Speed采样率:playback 和 capture 都为 48 KHz声道数:playback 和 capture 都为 2 Channels

位深度:playback 和 capture 都为 16 bitsNote:[1] 从Windows 10(1703 版)开始,Windows 才默认支持UAC 2.0 驱动程序。[2] Windows 和Linux 对音频事件的响应流程稍有不同,要做兼容性处理,Linux 和Android 一样。[3] Windows 会对设备驱动记忆,更改配置后最好卸载驱动,让Windows 重新识别设备。[4] 采样率,声道数,位深度都可以通过内核提供的接口配置,详细使用说明请查看UAC Usage。

2.3 UAC 使用

目前在 Rockchip 平台,UAC1/UAC2 在配置方法和实现功能上基本一致,只有在兼容性和协议上有所不同添加 defconfig对于 UAC1,添加 CONFIG_USB_CONFIGFS_F_UAC1=y 到内核的 defconfig对于 UAC2,添加 CONFIG_USB_CONFIGFS_F_UAC2=y 到内核的 defconfigLinux configfs 配置配置 Kernel-4.4/4.19 UAC1/UAC2 的脚本参考如下:

#!/bin/sh

UAC=uac2

USB_ATTRIBUTE=0x409
USB_GROUP=rockchip
USB_SKELETON=b.1

CONFIGFS_DIR=/sys/kernel/config
USB_CONFIGFS_DIR=${CONFIGFS_DIR}/usb_gadget/${USB_GROUP}
USB_STRINGS_DIR=${USB_CONFIGFS_DIR}/strings/${USB_ATTRIBUTE}
USB_FUNCTIONS_DIR=${USB_CONFIGFS_DIR}/functions
USB_CONFIGS_DIR=${USB_CONFIGFS_DIR}/configs/${USB_SKELETON}

function_init()
{
    mkdir ${USB_FUNCTIONS_DIR}/${UAC}.gs0
}

configfs_init()
{
    echo "Debug: configfs_init"
    mkdir /dev/usb-ffs

    mount -t configfs none ${CONFIGFS_DIR}
    mkdir ${USB_CONFIGFS_DIR} -m 0770
    echo 0x2207 > ${USB_CONFIGFS_DIR}/idVendor
    echo 0x0310 > ${USB_CONFIGFS_DIR}/bcdDevice
    echo 0x0200 > ${USB_CONFIGFS_DIR}/bcdUSB
    mkdir ${USB_STRINGS_DIR}   -m 0770
    SERIAL=`cat /proc/cpuinfo | grep Serial | awk '{print $3}'`
    if [ -z $SERIAL ];then
        SERIAL=0123456789ABCDEF
    fi
    echo $SERIAL > ${USB_STRINGS_DIR}/serialnumber
    echo "rockchip"  > ${USB_STRINGS_DIR}/manufacturer
    echo "uac-test"  > ${USB_STRINGS_DIR}/product

    function_init

    mkdir ${USB_CONFIGS_DIR}  -m 0770
    mkdir ${USB_CONFIGS_DIR}/strings/${USB_ATTRIBUTE}  -m 0770
}

parameter_init()
{
    if [ "$UAC" == "uac2" ]; then
        CONFIG_STRING=uac2
        echo "parameter_init ${CONFIG_STRING}"
    elif [ "$UAC" == "uac1" ];then
        CONFIG_STRING=uac1
        echo "parameter_init ${CONFIG_STRING}"
    else
        echo "parameter_init ${UAC} is invalid"
    fi
}

config_init()
{
    UAC_GS0=${USB_FUNCTIONS_DIR}/$1.gs0
    echo 3 > ${UAC_GS0}/p_chmask
    echo 2 > ${UAC_GS0}/p_ssize
    echo 8000,16000,44100,48000 > ${UAC_GS0}/p_srate
    echo ${FU} > ${UAC_GS0}/p_feature_unit
    echo 3 > ${UAC_GS0}/c_chmask
    echo 2 > ${UAC_GS0}/c_ssize
    echo 8000,16000,44100,48000 > ${UAC_GS0}/c_srate
    echo ${FU} > ${UAC_GS0}/c_feature_unit
}

syslink_function()
{
    ln -s ${USB_FUNCTIONS_DIR}/$1 ${USB_CONFIGS_DIR}/f${USB_FUNCTIONS_CNT}
    let USB_FUNCTIONS_CNT=USB_FUNCTIONS_CNT+1
}

bind_functions()
{
    USB_FUNCTIONS_CNT=1

    if [ "$UAC" == "uac2" ]; then
        syslink_function uac2.gs0
    elif [ "$UAC" == "uac1" ];then
        syslink_function uac1.gs0
    else
        echo "parameter_init ${UAC} is invalid"
    fi

    echo ${CONFIG_STRING} > ${USB_CONFIGS_DIR}/strings/${USB_ATTRIBUTE}/configuration
}

program_kill()
{
    P_PID=`ps | grep $1 | grep -v grep | awk '{print $1}'`
    test -z ${P_PID} || kill -9 ${P_PID}
}

usb_device_stop()
{
    echo "none" > ${USB_CONFIGFS_DIR}/UDC
    program_kill adbd
    program_kill mtp-server
    ls ${USB_CONFIGS_DIR} | grep f[0-9] | xargs -I {} rm ${USB_CONFIGS_DIR}/{}
}

case "$1" in
start)
    echo "usb_config in $1"
    DIR=$(cd `dirname $0`; pwd)
    parameter_init
    if [ -z $CONFIG_STRING ]; then
        echo "$0: no function be selected"
        exit 0
    fi
    test -d ${USB_CONFIGFS_DIR} || configfs_init
    echo 0x0019 > ${USB_CONFIGFS_DIR}/idProduct
    config_init
    bind_functions
    sleep 1
    UDC=`ls /sys/class/udc/| awk '{print $1}'`
    echo $UDC > ${USB_CONFIGFS_DIR}/UDC
    ;;
stop)
    usb_device_stop
    ;;
restart|reload)
    # Do restart usb by udev
    echo "USB_FORCE_CHANGED" >> /tmp/.usb_config
    usb_device_stop
    sleep 1
    $0 start
    # Don't forget to clear "USB_FORCE_CHANGED"
    sed -i "/USB_FORCE_CHANGED/d" /tmp/.usb_config
    ;;
*)
    echo "Usage: $0 {start|stop|restart}"
    exit 1
esac

exit 0

Note:[1] 直接运行uac.sh restart 即可切换到UAC1/UAC2[2] 修改变量${UAC} 可以指定UAC1 或者UAC2[3] “idProduct” 可以根据产品自行定义,但不能与产品的其他USB Function idProduct 冲突[4] Windows 会对设备驱动记忆,更改配置后最好卸载驱动,让Windows 重新识别设备Kernel-5.10 UAC1/UAC2 的配置已集成在 /oem/usr/bin/usb_config.sh 脚本中:

[...]

uac1_device_config()
{
  UAC=$1
  mkdir ${USB_FUNCTIONS_DIR}/${UAC}.gs0
  UAC_GS0=${USB_FUNCTIONS_DIR}/${UAC}.gs0
  echo 3 > ${UAC_GS0}/p_chmask
  echo 2 > ${UAC_GS0}/p_ssize
  echo 1 > ${UAC_GS0}/p_mute_present
  echo 1 > ${UAC_GS0}/p_volume_present
  echo -5120 > ${UAC_GS0}/p_volume_min #-20db min must > -96db
  echo 8000,16000,44100,48000 > ${UAC_GS0}/p_srate

  echo 3 > ${UAC_GS0}/c_chmask
  echo 2 > ${UAC_GS0}/c_ssize
  echo 4 > ${UAC_GS0}/req_number
  echo 1 > ${UAC_GS0}/c_mute_present
  echo 1 > ${UAC_GS0}/c_volume_present
  echo -3200 > ${UAC_GS0}/c_volume_min #-12.5db
  echo 0 > ${UAC_GS0}/c_volume_max   #0db
  echo 32 > ${UAC_GS0}/c_volume_res #0.125db
  echo 8000,16000,44100,48000 > ${UAC_GS0}/c_srate

  ln -s ${UAC_GS0} ${USB_CONFIGS_DIR}/f2
}
uac2_device_config()
{
  UAC=$1
  mkdir ${USB_FUNCTIONS_DIR}/${UAC}.gs0
  UAC_GS0=${USB_FUNCTIONS_DIR}/${UAC}.gs0
  echo 3 > ${UAC_GS0}/p_chmask
  echo 2 > ${UAC_GS0}/p_ssize
  echo 1 > ${UAC_GS0}/p_mute_present
  echo 1 > ${UAC_GS0}/p_volume_present
  echo -5120 > ${UAC_GS0}/p_volume_min #-20db min must > -96db
  echo 8000,16000,44100,48000 > ${UAC_GS0}/p_srate

  echo 3 > ${UAC_GS0}/c_chmask
  echo 2 > ${UAC_GS0}/c_ssize
  echo 4 > ${UAC_GS0}/req_number
  echo 1 > ${UAC_GS0}/c_mute_present
  echo 1 > ${UAC_GS0}/c_volume_present
  echo -3200 > ${UAC_GS0}/c_volume_min #-12.5db
  echo 0 > ${UAC_GS0}/c_volume_max   #0db
  echo 32 > ${UAC_GS0}/c_volume_res #0.125db
  echo 8000,16000,44100,48000 > ${UAC_GS0}/c_srate

  ln -s ${UAC_GS0} ${USB_CONFIGS_DIR}/f2
}

[...]

2.3.1 参数

查看 Kernel-4.4/Kernel-4.19 UAC1/UAC2 的 function 目录,可以发现以下参数接口:

[root@RV1126_RV1109:/sys/kernel/config/usb_gadget/rockchip/functions/uac1.gs0]# ls
c_chmask        c_srate  p_chmask        p_srate  req_number
c_feature_unit  c_ssize  p_feature_unit  p_ssize

其中 c 代表 capture,注意这里是 USB 虚拟声卡的录音通道,对应 Host 的放音;同理,p 表示 USB 虚拟声卡的playback 通道,对应 Host 的录音。两个通道互相独立。常用的参数接口设置如下:Sample Ratep_srate, c_srate默认值为单采样率 48000,支持多采样率配置,采样率之间用逗号隔开,例如:echo 8000,16000,44100,48000 > ${UAC_GS0}/c_srateChannelc_chmask, p_chmask默认值为 3(双声道),支持多声道或者删除对应声道。例如设置 UAC Device 为 5.1 录音声道,且不需要放音功能:echo 0x3F > p_chmaskecho 0 > c_chmaskData deepthp_ssize, c_ssize 默认值为 2 (单位:Bytes,即 16 位深度)Volumec_feature_unit, p_feature_unit 是音量控制的开关,默认是 0(关闭),写 1 可以开启。

因为 UAC2 的 Feature Unit 音量控制功能在 Windows 平台无法兼容,所以,建议 UAC1 启用 Feature Unit音量控制,UAC2 关闭 Feature Unit 音量控制。req_numberreq_number 为 UAC 驱动提交给 USB 控制器的 Buffer 个数。按照 USB 协议,当 USB Device 未准备好同步传输的数据时,允许回复 NO DATA 包;但 MAC OS 不能兼容这种行为。因此,在 CPU 高负载场景,可增加 req_number 个数以加大 UAC Buffer 缓存,从而增强不同 OS 的兼容性。Kernel-5.10 UAC1/UAC2 的 function 目录与 Kernel-4.4/Kernel-4.19 略有不同,具体参数如下:

#ls /sys/kernel/config/usb_gadget/rockchip/functions/uac1.gs0/
c_chmask          p_ssize           p_volume_max      c_volume_max
c_srate           req_number        p_volume_res      c_volume_res
c_ssize           p_mute_present    c_mute_present    function_name
p_chmask          p_volume_present  c_volume_present
p_srate           p_volume_min      c_volume_min

其中:volume/mute 的使能节点,由 c_feature_unit, p_feature_unit 变更为:p_mute_present/p_volume_present和 c_mute_present/c_volume_present。内核默认已经使能 volume/mute,SDK 方案 uac_app 默认可不控制。volume/mute 的 MIN_DB/MAX_DB/RES_DB 分别变更为 -100 dB/0 dB/1 dB,同时,内核提供节点p_volume_max/p_volume_min/p_volume_res 以及 c_volume_max/c_volume_min/c_volume_res,供产品开发时根据 codec 特性重新配置这些参数。Note:[1] volume/mute 需要uac_app 进行适配,以根据PC 音量滑块,更线性地控制codec 输出,可参考文献Windows Audio-Tapered Volume Controls.[2] 设备端定义的MIN_DB/MAX_DB,将会在UAC 枚举时,反馈给PC,PC 继而会根据这两个值,设置PC 端音量滑块的0 和100 分别对应为MIN_DB 和MAX_DB。

2.3.2 Uevent

为了准确控制音频数据的通断,以及多采样率和音量的设置,应用层 uac_app 需要收到并响应内核的事件。这里我们使用 uevent 事件完成内核到应用层的通知,应用层监控 uac 节点,提取事件中的关键字符串信息。start/stop

g_audio_work: sent uac uevent USB_STATE=SET_INTERFACE STREAM_DIRECTION=IN STREAM_STATE=OFF
g_audio_work: sent uac uevent USB_STATE=SET_INTERFACE STREAM_DIRECTION=OUT STREAM_STATE=ON

multi sample

g_audio_work: sent uac uevent USB_STATE=SET_SAMPLE_RATE STREAM_DIRECTION=OUT SAMPLE_RATE=44100

volume/mute

g_audio_work: sent uac uevent USB_STATE=SET_VOLUME STREAM_DIRECTION=IN VOLUME=-1154
g_audio_work: sent uac uevent USB_STATE=SET_VOLUME STREAM_DIRECTION=IN VOLUME=-350
g_audio_work: sent uac uevent USB_STATE=SET_VOLUME STREAM_DIRECTION=IN VOLUME=0
g_audio_work: sent uac uevent USB_STATE=SET_VOLUME STREAM_DIRECTION=IN VOLUME=1739
g_audio_work: sent uac uevent USB_STATE=SET_VOLUME STREAM_DIRECTION=IN VOLUME=2612

Note:[1] 这里的IN 表示Host 录音,OUT 表示Host 放音。[2] Kernel-4.4/Kernel-4.19 内核UAC1/UAC2 驱动会自动将PC 设置的 Volume control 原始值转换为Volume 百分比后通过Uevent 上报于uac_app。[3] Kernel-5.10 volume 直接上报PC 设置的 volume control 原始值,uvc_app 需要将内核上报的值转换为相应codec对应的db 值。其转化参考公式如下:

// volume control 与 db 的转换公式
#define VOLUME_USB_TO_DB(v_usb) (v_usb <= 0x7FFF) ? v_usb : (-(((rt_int16_t)0xFFFF - v_usb) + 1))

// uac_app 将 db 转化为⾳量的⽅法
P：百分⽐；a：当前⾳量分⻉值；m：最⼤⾳量分⻉值
P = 10 ^ [(a - m)/10]
a = 10 * lg(P) + m

2.3.3 PPM 补偿

因为 USB 的时钟来自于 Host,Codec 的时钟来自于 Device,异源的时钟会导致音频数据丢失,具体表现在 alsa 周期性地打印 underrun/overrun。为了解决异源时钟的问题,我们提出 ppm compensation 的解决方案,通过记录 Host 每 128us 发送的一次的 SOF包对比系统时间,计算一定时间内的 ppm 差值,然后通过 uevent 事件上报到应用层:

g_audio_work: sent uac uevent USB_STATE=SET_AUDIO_CLK PPM=12
g_audio_work: sent uac uevent USB_STATE=SET_AUDIO_CLK PPM=-1

只要 USB 有连接,就会一直计算 ppm,应用层通过监听 uvent 就获取到具体的 ppm 值然后通过 codec 提供的接口调整 codec 的时钟。Note:这种方法测试的ppm 值会随着时间增加越来越稳定,一般十分钟后就不会有新的ppm 值上报了。如果USB 有断开,SOF 就会重新计数,ppm 会先回归到0 再逐渐稳定到新的值如果对实时性要求不高,应用层可以忽略上报的ppm 补偿值

2.3.4 兼容性

Volume Control如果在 Windows 系统上使用 UAC2,音量控制一定是要关闭的,即 UAC2 的 c_feature_unit, p_feature_unit 设置为0,否则 Windows 无法正常加载 UAC2 驱动。表 2-1 不同主机系统对 UAC 音量控制的支持情况

	Windows10	Linux(ubuntu)	MacOS
UAC1	支持	不支持	支持
UAC2	驱动异常	不支持	支持

2.4 UAC 测试

UAC1 和 UAC2 的测试方法完全一样,这里以 UAC1 为例配置脚本执行成功后,连接 USB 到 PC,PC 端可以识别到 USB Audio 设备,如下图 2-1 Windows-USB-Audio-Class1,图 2-2 Ubuntu-USB-Audio-Class1-Output 和图 2-3 Ubuntu-USB-Audio-Class1-Input。

原稿配图 — PDF p16

图 2-1 Windows-USB-Audio-Class1

原稿配图 — PDF p17

图 2-2 Ubuntu-USB-Audio-Class1-Output

原稿配图 — PDF p17

图 2-3 Ubuntu-USB-Audio-Class1-InputRK3308 端的串口打印如下 USB UAC1 正常枚举的日志:

dwc2 ff400000.usb: new device is high-speed
dwc2 ff400000.usb: new address 19
android_work: sent uevent USB_STATE=CONNECTED
configfs-gadget gadget: high-speed config #1: b
android_work: sent uevent USB_STATE=CONFIGURED

查看 UAC1 声卡信息的方法:如下显示的结果,UAC1 对应 card2 (UAC1Gadget),具有一个 playback 设备节点 - pcmC2D0p 和一个 capture 设备节点 - pcmC2D0c。

# cat /proc/asound/cards
 0 [rockchiprk3308v]: rockchip_rk3308 - rockchip,rk3308-vad
                      rockchip,rk3308-vad
 1 [rockchiprk3308p]: rockchip_rk3308 - rockchip,rk3308-pcm
                      rockchip,rk3308-pcm
 2 [UAC1Gadget     ]: UAC1_Gadget - UAC1_Gadget
                      UAC1_Gadget 0
 7 [Loopback       ]: Loopback - Loopback
                      Loopback 1

# ls -lh /proc/asound/card2
-r--r--r--    1 root     root           0 Dec 31 19:14 id
dr-xr-xr-x    3 root     root           0 Dec 31 19:14 pcm0c
dr-xr-xr-x    3 root     root           0 Dec 31 19:14 pcm0p

# ls /dev/snd/
controlC0  controlC7  pcmC1D0c   pcmC2D0p   pcmC7D1c
controlC1  pcmC0D0c   pcmC1D0p   pcmC7D0c   pcmC7D1p
controlC2  pcmC0D0p   pcmC2D0c   pcmC7D0p   timer

2.4.1 Windows UAC 测试

打开 Windows 声音设置,如下图 2-4 Windows-Audio-Setting,分别选择 USB-Audio 作为声音输出设备和声音输入设备(⻨克⻛)。

原稿配图 — PDF p19

图 2-4 Windows-Audio-Setting测试 Windows UAC1 放音功能:在 RK3308 端的串口执行如下的 UAC1 放音命令:

arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 | aplay -f dat -r 48000 -c 2 -D hw:0,0

上述命令表示从 Card2(USB Audio)录音,然后从本地声卡 Card0 播放声音执行完命令后,Windows PC 端播放音乐,RK3308 本地声卡可以实时放音。测试 Windows UAC1 录音功能:测试录音功能,需要使用可以播放的音频文件。通过 ADB push 或者 arecord 的方法,保存测试使用的音频文件(要求 48KHz,2 channels,16 bits)

比如,RK3308 端的串口执行 arecord 命令,保存测试使用的音频文件 test.wav

arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 /tmp/test.wav

保存音频文件 test.wav 成功后,再执行如下的 UAC1 录音命令:

aplay /tmp/test.wav -c 2 -r 48000 -D hw:2,0

执行完上述命令后,PC 端可以使用 Windows 自带的 “Voice Recorder”软件保存录音文件,如下图 2-5 Windows-Voice-Recorder。

原稿配图 — PDF p20

图 2-5 Windows-Voice-Recorder除了上述的录音测试方法,也可以使用 Windows 的录音侦听功能,实时播放录音的音频,方法如下:打开“声音设置” –> “声音控制面板” –> “录制” –> “属性” –> “侦听” ,勾选“侦听此设备”,并选择播放的扬声器。如下图 2-6 Windows-Capture-Listen-1 和图 2-7 Windows-Capture-Listen-2。

原稿配图 — PDF p21

图 2-6 Windows-Capture-Listen-1

原稿配图 — PDF p22

图 2-7 Windows-Capture-Listen-2

2.4.2 Ubuntu UAC 测试

打开 Ubuntu 声音设置,如下图 2-8 Ubuntu-Audio-Setting-Output 和图 2-9 Ubuntu-Audio-Setting-Input,分别选择 USB-Audio 作为声音输出设备和声音输入设备(⻨克⻛)。

原稿配图 — PDF p23

图 2-8 Ubuntu-Audio-Setting-Output

原稿配图 — PDF p23

图 2-9 Ubuntu-Audio-Setting-Input测试 Ubuntu UAC1 放音功能:在 RK3308 端的串口执行如下的 UAC1 放音命令:

arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 | aplay -f dat -r 48000 -c 2 -D hw:0,0

上述命令表示从 Card2(USB Audio)录音,然后从本地声卡 Card0 播放声音执行完命令后,Ubuntu PC 端播放音乐,RK3308 本地声卡可以实时放音。测试 Ubuntu UAC1 录音功能:测试录音功能,需要使用可以播放的音频文件。通过 ADB push 或者 arecord 的方法,保存测试使用的音频文件(要求 48KHz,2 channels,16 bits)比如,RK3308 端的串口执行 arecord 命令,保存测试使用的音频文件 test.wav

arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 /tmp/test.wav

保存音频文件 test.wav 成功后,再执行如下的 UAC1 录音命令:

aplay /tmp/test.wav -c 2 -r 48000 -D hw:2,0

执行完上述命令后,在 Ubuntu 端打开录音软件,如“audacity”,进行录音功能测试。audacity 安装命令:

sudo apt install audacity

audacity 录音界面如下图 2-10 所示。

原稿配图 — PDF p24

图 2-10 Ubuntu-audacity

3. UAC1 Legacy 使用与测试

3.1 UAC1 Legacy 使用

参数默认值说明：audio_buf_size为音频缓冲48000；fn_cap为采集PCM设备 /dev/snd/pcmC0D0c；fn_cntl为控制设备 /dev/snd/controlC0；fn_play为播放设备 /dev/snd/pcmC0D0p；req_buf_size为ISO OUT请求缓冲200；req_count为ISO OUT请求数256。

Rockchip 平台 UAC1 Legacy 驱动兼容 USB Audio Class specification 1.0,但只支持放音功能,并且需要实际的声卡支持(默认使用 /dev/snd/pcmC0D0p)。默认支持:速率:High Speed采样率:playback 48 KHz,不可配置声道数:playback 2 Channels,不可配置位深度:playback 16 bitsUAC1 Legacy 使用方法如下:添加 CONFIG_USB_CONFIGFS_F_UAC1_LEGACY=y 到内核的 defconfig以 RK3308 EVB 为例配置 UAC1 Legacy 的脚本参考如下:

mount -t configfs none /sys/kernel/config
mkdir /sys/kernel/config/usb_gadget/rockchip  -m 0770
echo 0x2207 > /sys/kernel/config/usb_gadget/rockchip/idVendor
echo 0x0019 > /sys/kernel/config/usb_gadget/rockchip/idProduct
echo 0x0100 > /sys/kernel/config/usb_gadget/rockchip/bcdDevice
mkdir /sys/kernel/config/usb_gadget/rockchip/strings/0x409   -m 0770
echo "0123456789ABCDEF" > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/serialnumber
echo "rockchip"  > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/manufacturer
echo "USB Audio Device"  > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/product
mkdir /sys/kernel/config/usb_gadget/rockchip/configs/b.1  -m 0770
mkdir /sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409  -m 0770
echo 500 > /sys/kernel/config/usb_gadget/rockchip/configs/b.1/MaxPower
echo "uac1" > /sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409/configuration
mkdir /sys/kernel/config/usb_gadget/rockchip/functions/uac1_legacy.gs0
ln -s /sys/kernel/config/usb_gadget/rockchip/functions/uac1_legacy.gs0
/sys/kernel/config/usb_gadget/rockchip/configs/b.1/uac1_legacy.gs0
echo ff400000.usb > /sys/kernel/config/usb_gadget/rockchip/UDC

假如 RK3308 开机后,默认运行了 ADB 配置脚本,会导致上述的配置方法出错,在调试阶段,可以手动执行如下命令来配置 UAC1 Legacy 功能。最终产品的 USB 配置脚本,需要根据实际的需求来整合 ADB 和 UAC1 Legacy 的配置脚本。

rm -rf /sys/kernel/config/usb_gadget/rockchip/configs/b.1/ffs.adb

mkdir /sys/kernel/config/usb_gadget/rockchip/functions/uac1_legacy.gs0
echo 0x0019 > /sys/kernel/config/usb_gadget/rockchip/idProduct
echo 0x0100 > /sys/kernel/config/usb_gadget/rockchip/bcdDevice
echo "USB Audio Device" > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/product
echo "uac1" > /sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409/configuration
cd /sys/kernel/config/usb_gadget/rockchip/configs/b.1
ln -s ../../functions/uac1_legacy.gs0

echo ff400000.usb > ../../UDC

Note:“idProduct ” 可以根据产品自行定义,但不能与产品的其他USB Function idProduct 冲突“UDC” 为USB 控制器名称,对应/sys/class/udc/控制器名称Windows 会对设备驱动记忆,更改配置后最好卸载驱动,让Windows 重新识别设备配置脚本执行成功后,连接 USB 到 PC,PC 端可以识别到 USB Audio 设备,如图 3-1

原稿配图 — PDF p26

图 3-1 Windows-USB-Audio-Class1-LegacyRK3308 端的串口打印如下 USB UAC1 Legacy 正常枚举的日志:

configfs-gadget gadget: Hardware params: access 3, format 2, channels 2, rate 48000
dwc2 ff400000.usb: bound driver configfs-gadget
dwc2 ff400000.usb: new device is high-speed
dwc2 ff400000.usb: new address 25
android_work: sent uevent USB_STATE=CONNECTED
configfs-gadget gadget: high-speed config #1: b
android_work: sent uevent USB_STATE=CONFIGURED

UAC1 Legacy 驱动提供如下的配置接口:如下配置无法动态生效,也即必须添加在 UAC 的配置脚本中执行。

# ls -lh /sys/kernel/config/usb_gadget/g1/functions/uac1_legacy.gs0/
-rw-r--r--    1 root     root        4.0K Dec 31 19:08 audio_buf_size
-rw-r--r--    1 root     root        4.0K Dec 31 19:08 fn_cap
-rw-r--r--    1 root     root        4.0K Dec 31 19:08 fn_cntl
-rw-r--r--    1 root     root        4.0K Dec 31 19:08 fn_play
-rw-r--r--    1 root     root        4.0K Dec 31 19:08 req_buf_size
-rw-r--r--    1 root     root        4.0K Dec 31 19:08 req_count

audio_buf_size - audio buffer size 默认设置为 48000
fn_cap - capture pcm device file name 默认设置为 /dev/snd/pcmC0D0c
fn_cntl - control device file name 默认设置为 /dev/snd/controlC0
fn_play - playback pcm device file name 默认设置为 /dev/snd/pcmC0D0p
req_buf_size - ISO OUT endpoint request buffer size 默认设置为 200
req_count - ISO OUT endpoint request count 默认设置为 256

UAC1 Legacy 不会在 RK3308 端创建对应的声卡设备节点。

3.2 UAC1 Legacy 测试

Windows PC 端的放音设置请参考 UAC Test on WindowsUbuntu PC 端的放音设置请参考 UAC Test on UbuntuRK3308 端不需要执行任何命令,连接 USB 到 PC 后,UAC1 Legacy 驱动默认会打开 RK3308 本地 Card0 声卡播放声音。

4. Audio Source 使用与测试

4.1 Audio Source 使用

Rockchip 平台 Audio Source 驱动兼容 USB Audio Class specification 1.0,但只支持录音功能。默认支持:速率:High Speed采样率:playback 默认使用 44.1KHz,总共支持如下 15 种不同的采样率,PC 端可以动态配置

8000, 11025, 16000, 22050, 24000,
32000, 40000, 44100, 48000, 56000,
64000, 72000, 80000, 88200, 96000,

声道数:playback 2 Channels,不可配置位深度:playback 16 bitsAudio Source 使用方法如下:添加 CONFIG_USB_CONFIGFS_F_ACC=y(Audio Source depends on it)到内核的 defconfig添加 CONFIG_USB_CONFIGFS_F_AUDIO_SRC=y 到内核的 defconfig

以 RK3308 EVB 为例配置 Audio Source 的脚本参考如下:

mount -t configfs none /sys/kernel/config
mkdir /sys/kernel/config/usb_gadget/rockchip  -m 0770
echo 0x2207 > /sys/kernel/config/usb_gadget/rockchip/idVendor
echo 0x0019 > /sys/kernel/config/usb_gadget/rockchip/idProduct
mkdir /sys/kernel/config/usb_gadget/rockchip/strings/0x409   -m 0770
echo "0123456789ABCDEF" > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/serialnumber
echo "rockchip"  > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/manufacturer
echo "USB Audio Device"  > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/product
mkdir /sys/kernel/config/usb_gadget/rockchip/configs/b.1  -m 0770
mkdir /sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409  -m 0770
echo 500 > /sys/kernel/config/usb_gadget/rockchip/configs/b.1/MaxPower
echo "audio" >
/sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409/configuration
mkdir /sys/kernel/config/usb_gadget/rockchip/functions/audio_source.gs0
ln -s /sys/kernel/config/usb_gadget/rockchip/functions/audio_source.gs0
/sys/kernel/config/usb_gadget/rockchip/configs/b.1/audio_source.gs0
echo ff400000.usb > /sys/kernel/config/usb_gadget/rockchip/UDC

假如 RK3308 开机后,默认运行了 ADB 配置脚本,会导致上述的配置方法出错,在调试阶段,可以手动执行如下命令来配置 Audio Source 功能。最终产品的 USB 配置脚本,需要根据实际的需求来整合 ADB 和 Audio Source 的配置脚本。

rm -rf /sys/kernel/config/usb_gadget/rockchip/configs/b.1/ffs.adb

mkdir /sys/kernel/config/usb_gadget/rockchip/functions/audio_source.gs0
echo 0x0019 > /sys/kernel/config/usb_gadget/rockchip/idProduct
echo 0x0100 > /sys/kernel/config/usb_gadget/rockchip/bcdDevice
echo "USB Audio Device" > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/product
echo "audio" >
/sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409/configuration
cd /sys/kernel/config/usb_gadget/rockchip/configs/b.1
ln -s ../../functions/audio_source.gs0

echo ff400000.usb > ../../UDC

原稿配图 — PDF p29

图 4-1 Windows-USB-Audio-Source

原稿配图 — PDF p29

图 4-2 Ubuntu-USB-Audio-SourceRK3308 端的串口打印如下 USB Audio Source 正常枚举的日志:

dwc2 ff400000.usb: new device is high-speed
dwc2 ff400000.usb: new address 23
android_work: sent uevent USB_STATE=CONNECTED
configfs-gadget gadget: high-speed config #1: b
android_work: sent uevent USB_STATE=CONFIGURED

Audio Source 驱动没有提供可配置的内核接口。查看 Audio Source 信息的方法:如下显示的结果,Audio Source 对应 card2 (audiosource),只有一个 playback 设备节点 - pcmC2D0p。

# cat /proc/asound/cards
 0 [rockchiprk3308v]: rockchip_rk3308 - rockchip,rk3308-vad
                      rockchip,rk3308-vad
 1 [rockchiprk3308p]: rockchip_rk3308 - rockchip,rk3308-pcm
                      rockchip,rk3308-pcm
 2 [audiosource    ]: audio_source - audio_source
                      USB accessory audio source
 7 [Loopback       ]: Loopback - Loopback
                      Loopback 1

# ls -lh /proc/asound/card2
-r--r--r--    1 root     root           0 Dec 31 19:06 id
dr-xr-xr-x    3 root     root           0 Dec 31 19:06 pcm0p

# ls /dev/snd/
controlC0  controlC2  pcmC0D0c   pcmC1D0c   pcmC2D0p   pcmC7D0p   pcmC7D1p
controlC1  controlC7  pcmC0D0p   pcmC1D0p   pcmC7D0c   pcmC7D1c   timer

4.2 Audio Source 测试

测试 Audio Source 录音功能:Windows PC 端的录音设置请参考 UAC Test on WindowsUbuntu PC 端的录音设置请参考 UAC Test on UbuntuRK3308 端的测试命令(假设采样率使用默认的 44.1KHz):

aplay /tmp/test.wav -r 44100 -c 2 -D hw:2,0

Note:测试使用的音频文件test.wav 的采样率,应与录音的采样率一致,否则,测试时可能出现杂音或者无声音此外,因为 Audio Source 支持 15 种不同的采样率,所以 PC 端可以动态配置采样率,方法如下:打开“声音设置” –> “声音控制面板” –> “录制” –> “属性” –> “高级”,选择对应的采样率。如下图 4-3 所示。

原稿配图 — PDF p31

图 4-3 Windows-USB-Audio-Source-Setting

5. UAC1 Legacy 与 Audio Source 复合使用及测试

5.1 复合设备使用

UAC1 Legacy + Audio Source 使用方法如下:UAC1 Legacy 和 Audio Source 可以组合为一个 USB 复合设备,支持录音和放音功能。添加 CONFIG_USB_CONFIGFS_F_UAC1_LEGACY=y 到内核的 defconfig添加 CONFIG_USB_CONFIGFS_F_ACC=y(Audio Source depends on it)到内核的 defconfig添加 CONFIG_USB_CONFIGFS_F_AUDIO_SRC=y 到内核的 defconfig此外,需要单独更新补丁“support_uac1_legacy_and_audio_source.patch”。以 RK3308 EVB 为例配置 UAC1 Legacy + Audio Source 的脚本参考如下:

mount -t configfs none /sys/kernel/config
mkdir /sys/kernel/config/usb_gadget/rockchip  -m 0770
echo 0x2207 > /sys/kernel/config/usb_gadget/rockchip/idVendor
echo 0x0019 > /sys/kernel/config/usb_gadget/rockchip/idProduct
echo 0x0100 > /sys/kernel/config/usb_gadget/rockchip/bcdDevice
mkdir /sys/kernel/config/usb_gadget/rockchip/strings/0x409   -m 0770
echo "0123456789ABCDEF" > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/serialnumber
echo "rockchip"  > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/manufacturer
echo "USB Audio Device"  > /sys/kernel/config/usb_gadget/rockchip/strings/0x409/product
mkdir /sys/kernel/config/usb_gadget/rockchip/configs/b.1  -m 0770
mkdir /sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409  -m 0770
echo 500 > /sys/kernel/config/usb_gadget/rockchip/configs/b.1/MaxPower
echo "uac1" > /sys/kernel/config/usb_gadget/rockchip/configs/b.1/strings/0x409/configuration
mkdir /sys/kernel/config/usb_gadget/rockchip/functions/uac1_legacy.gs0
ln -s /sys/kernel/config/usb_gadget/rockchip/functions/uac1_legacy.gs0
/sys/kernel/config/usb_gadget/rockchip/configs/b.1/uac1_legacy.gs0
mkdir /sys/kernel/config/usb_gadget/rockchip/functions/audio_source.gs0
ln -s /sys/kernel/config/usb_gadget/rockchip/functions/audio_source.gs0
/sys/kernel/config/usb_gadget/rockchip/configs/b.1/audio_source.gs0
echo ff400000.usb > /sys/kernel/config/usb_gadget/rockchip/UDC

其他配置和调试方法,请参考 UAC1 Legacy Usage 和 Audio Source Usage

5.2 复合设备测试

请参考 UAC1 Legacy Test 和 Audio Source Test

6. 参考文档

USB Protocol (from USB Implementers Forum)Universal Serial Bus Specification, Revision 2.0Universal Serial Bus Audio Device Class Specification for Basic Audio DevicesUniversal Serial Bus Device Class Definition for Audio Devices, Release 1.0Universal Serial Bus Device Class Definition for Audio Devices, Release 2.0Universal Serial Bus Device Class Definition for Audio Data Formats(referred to in this document asUSB Audio Data Formats)Universal Serial Bus Device Class Definition for Terminal Types(referred to in this document as USBAudio Terminal Types)OthersThe Well-Tempered Computer (An introduction to computer audio) - USBWindows USB Audio 2.0 DriversWindows Audio-Tapered Volume Controls

7. 附录 A：UAC1 设备描述符

Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x2207
  idProduct          0x0019
  bcdDevice            1.00
  iManufacturer           1 rockchip
  iProduct                2 USB Audio Device
  iSerial                 3 0123456789ABCDEF
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength          174
    bNumInterfaces          3
    bConfigurationValue     1
    iConfiguration          4 audio
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      1 Control Device
      bInterfaceProtocol      0
      iInterface              5 AC Interface
      AudioControl Interface Descriptor:
        bLength                10
        bDescriptorType        36
        bDescriptorSubtype      1 (HEADER)
        bcdADC               1.00
        wTotalLength           52
        bInCollection           2
        baInterfaceNr( 0)       1
        baInterfaceNr( 1)       2
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             1
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bNrChannels             2
        wChannelConfig     0x0003
          Left Front (L)
          Right Front (R)
        iChannelNames           7 Playback Channels
        iTerminal               6 Playback Input terminal
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             2
        wTerminalType      0x0301 Speaker
        bAssocTerminal          0
        bSourceID               1
        iTerminal               8 Playback Output terminal
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             3
        wTerminalType      0x0201 Microphone
        bAssocTerminal          0
        bNrChannels             2
        wChannelConfig     0x0003
          Left Front (L)
          Right Front (R)
        iChannelNames          10 Capture Channels
        iTerminal               9 Capture Input terminal
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             4
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bSourceID               3
        iTerminal              11 Capture Output terminal
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface             12 Playback Inactive
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface             13 Playback Active
      AudioStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           1
        bDelay                  1 frames
        wFormatTag              1 PCM
      AudioStreaming Interface Descriptor:
        bLength                11
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bNrChannels             2
        bSubframeSize           2
        bBitResolution         16
        bSamFreqType            1 Discrete
        tSamFreq[ 0]        48000
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            9
          Transfer Type            Isochronous
          Synch Type               Adaptive
          Usage Type               Data
        wMaxPacketSize     0x00c8  1x 200 bytes
        bInterval               4
        bRefresh                0
        bSynchAddress           0
        AudioControl Endpoint Descriptor:
          bLength                 7
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x01
            Sampling Frequency
          bLockDelayUnits         1 Milliseconds
          wLockDelay              1 Milliseconds
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface             14 Capture Inactive
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0
      iInterface             15 Capture Active
      AudioStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           4
        bDelay                  1 frames
        wFormatTag              1 PCM
      AudioStreaming Interface Descriptor:
        bLength                11
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bNrChannels             2
        bSubframeSize           2
        bBitResolution         16
        bSamFreqType            1 Discrete
        tSamFreq[ 0]        48000
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x00c8  1x 200 bytes
        bInterval               4
        bRefresh                0
        bSynchAddress           0
        AudioControl Endpoint Descriptor:
          bLength                 7
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x01
            Sampling Frequency
          bLockDelayUnits         0 Undefined
          wLockDelay              0 Undefined
Device Qualifier (for other device speed):
  bLength                10
  bDescriptorType         6
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  bNumConfigurations      1
Device Status:     0x0000
  (Bus Powered)

8. 附录 B：UAC2 设备描述符

Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  idVendor           0x2207
  idProduct          0x0019
  bcdDevice            2.00
  iManufacturer           1 rockchip
  iProduct                2 USB Audio Device
  iSerial                 3 0123456789ABCDEF
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength          219
    bNumInterfaces          3
    bConfigurationValue     1
    iConfiguration          4 audio
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              500mA
    Interface Association:
      bLength                 8
      bDescriptorType        11
      bFirstInterface         0
      bInterfaceCount         3
      bFunctionClass          1 Audio
      bFunctionSubClass       0
      bFunctionProtocol      32
      iFunction               5 Source/Sink
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      1 Control Device
      bInterfaceProtocol     32
      iInterface              6 Topology Control
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      1 (HEADER)
        bcdADC               2.00
        bCategory               8
        wTotalLength           83
        bmControl            0x00
      AudioControl Interface Descriptor:
        bLength                 8
        bDescriptorType        36
        bDescriptorSubtype     10 (CLOCK_SOURCE)
        bClockID                6
        bmAttributes         0x01 Internal fixed Clock
        bmControls           0x01
          Clock Frequency Control (read-only)
        bAssocTerminal          0
        iClockSource            7 48000Hz
      AudioControl Interface Descriptor:
        bLength                 8
        bDescriptorType        36
        bDescriptorSubtype     10 (CLOCK_SOURCE)
        bClockID                5
        bmAttributes         0x01 Internal fixed Clock
        bmControls           0x01
          Clock Frequency Control (read-only)
        bAssocTerminal          0
        iClockSource            8 64000Hz
      AudioControl Interface Descriptor:
        bLength                17
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             1
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bCSourceID              5
        bNrChannels             2
        bmChannelConfig   0x00000003
          Front Left (FL)
          Front Right (FR)
        bmControls    0x0003
          Copy Protect Control (read/write)
        iChannelNames           0
        iTerminal               9 USBH Out
      AudioControl Interface Descriptor:
        bLength                17
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             2
        wTerminalType      0x0201 Microphone
        bAssocTerminal          0
        bCSourceID              6
        bNrChannels             2
        bmChannelConfig   0x00000003
          Front Left (FL)
          Front Right (FR)
        bmControls    0x0003
          Copy Protect Control (read/write)
        iChannelNames           0
        iTerminal              10 USBD Out
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             4
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bSourceID               2
        bCSourceID              6
        bmControls         0x0003
          Copy Protect Control (read/write)
        iTerminal              11 USBH In
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             3
        wTerminalType      0x0301 Speaker
        bAssocTerminal          0
        bSourceID               1
        bCSourceID              5
        bmControls         0x0003
          Copy Protect Control (read/write)
        iTerminal              12 USBD In
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol     32
      iInterface             13 Playback Inactive
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol     32
      iInterface             14 Playback Active
      AudioStreaming Interface Descriptor:
        bLength                16
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           1
        bmControls           0x00
        bFormatType             1
        bmFormats         0x00000001
          PCM
        bNrChannels             2
        bmChannelConfig   0x00000003
          Front Left (FL)
          Front Right (FR)
        iChannelNames           0
      AudioStreaming Interface Descriptor:
        bLength                 6
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bSubslotSize            2
        bBitResolution         16
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            9
          Transfer Type            Isochronous
          Synch Type               Adaptive
          Usage Type               Data
        wMaxPacketSize     0x0100  1x 256 bytes
        bInterval               4
        AudioControl Endpoint Descriptor:
          bLength                 8
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x00
          bmControls           0x00
          bLockDelayUnits         0 Undefined
          wLockDelay              0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol     32
      iInterface             15 Capture Inactive
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol     32
      iInterface             16 Capture Active
      AudioStreaming Interface Descriptor:
        bLength                16
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           4
        bmControls           0x00
        bFormatType             1
        bmFormats         0x00000001
          PCM
        bNrChannels             2
        bmChannelConfig   0x00000003
          Front Left (FL)
          Front Right (FR)
        iChannelNames           0
      AudioStreaming Interface Descriptor:
        bLength                 6
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bSubslotSize            2
        bBitResolution         16
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes           13
          Transfer Type            Isochronous
          Synch Type               Synchronous
          Usage Type               Data
        wMaxPacketSize     0x00c0  1x 192 bytes
        bInterval               4
        AudioControl Endpoint Descriptor:
          bLength                 8
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x00
          bmControls           0x00
          bLockDelayUnits         0 Undefined
          wLockDelay              0
Device Qualifier (for other device speed):
  bLength                10
  bDescriptorType         6
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0
  bDeviceProtocol         0
  bMaxPacketSize0        64
  bNumConfigurations      1
Device Status:     0x0000
  (Bus Powered)