ArmSoM platform reference from Chinese RK-KF-YF-098 V1.3.1. The source covers Rockchip chips except MCUs and Linux 4.4 or later; this does not establish adaptation of every ArmSoM board. Verify board, SoC, SDK/BSP, kernel patches, USB interface and codec. Logs/tests are source examples, not ArmSoM measurements; no hardware validation was performed. Only a Chinese PDF was supplied; all languages use its original figures.
Source ambiguities retained: Full/High Speed is written as 12/480 MHz; 176 kHz as 1056 bytes; 60×24×96 kHz as 132 Mbit/s; SOF period as 128us. These units/calculations require checking, not silent replacement. The Kernel-5.10 volume paragraph says uvc_app while other passages say uac_app. Verify Windows UAC2 Feature Unit limitations against newer-kernel defaults in the actual BSP. Examples remove configfs links and switch USB functions, potentially interrupting ADB; none were executed.
Source technical preface: UAC1/UAC2 support basic recording/playback; UAC1 Legacy needs a real sound card and supports playback only; Audio Source supports recording only with 15 sample rates. Select according to product needs. Physical device buttons for volume/mute need additional HID control, not supported by the SDK described in the source. Development references:
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
1. Kernel UAC configuration
1.1 Related kernel commits
Update the Kernel-5.10 UAC1/UAC2 code to at least the following commit for full functionality.
usb: gadget: u_audio: add uevent for ppm compensation
For Kernel-4.4/4.19 UAC1/UAC2, first verify that the kernel includes the following patch series. If the patches are absent, report the issue through Rockchip Redmine or contact the source-document author. Patch list:
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 Related configuration
CONFIG_USB_CONFIGFS_F_UAC1 enables UAC1; CONFIG_USB_CONFIGFS_F_UAC2 enables UAC2; CONFIG_USB_CONFIGFS_F_UAC1_LEGACY enables UAC1 Legacy; CONFIG_USB_CONFIGFS_F_ACC is required by Audio Source; CONFIG_USB_CONFIGFS_F_AUDIO_SRC enables Audio Source.
1.3 Related documents
Documentation/usb/gadget_configfs.txt
Documentation/usb/gadget-testing.txt
Documentation/ABI/testing/configfs-usb-gadget-uac1
Documentation/ABI/testing/configfs-usb-gadget-uac1_legacy
Documentation/ABI/testing/configfs-usb-gadget-uac2
1.4 Support list
Table 1-1. UAC1/UAC2 device features on Rockchip.
| Function | Uevent control | Multiple sample rates | Multiple channels | Feature Unit volume | Clock synchronization |
|---|---|---|---|---|---|
| UAC1 | YES | YES | YES | YES | YES |
| UAC2 | YES | YES | YES | YES | YES |
[1] Uevent control means that the kernel sends UAC start/stop, sample-rate and volume events to userspace uac_app to control the sound card; see Uevent. [2] UAC2 Feature Unit volume control is incompatible with Windows. Enable it for UAC1 and disable it for UAC2; see UAC Usage. [3] Clock synchronization dynamically adjusts the audio-clock frequency to synchronize USB host and audio-device clocks. In the source SDK, only RV1126-Linux-4.19 supports this; see PPM Compensation.
2. UAC1/UAC2 usage and tests
2.1 UAC1 information
USB Audio Class 1 standard (1998): the source describes a maximum of 24 bits/96 kHz, while the standard itself imposes no sample-rate limit. Class 1 is tied to USB 1 Full Speed, stated as 12 MHz in the source. One packet is sent each millisecond, with a maximum of 1023 bytes. Two channels × 24 bit × 96000 Hz = 4608000 bits/s or 576 Byte/ms, within that limit.
The source states that a higher common rate such as 176 kHz requires 1056 bytes, exceeding the packet limit. Win, OSX and Linux support Class 1 natively: no driver installation, plug-and-play, two channels at 24 bits/96 kHz. Rockchip UAC1 implements USB Audio Class specification 1.0 with capture and playback and needs no physical sound card. It sets bInterval=4. Defaults: High Speed; playback/capture 48 KHz; two channels each; 16 bits each. [1] Audio 1.0 predates USB 2.0 and has no High Speed concept. Empirical rules, such as isochronous endpoint bInterval=4, allow High Speed on particular OSs. The source reports operation on various platforms and better compatibility than UAC2 across Windows versions. [2] Kernel interfaces configure sample rate, channels and bit depth; see UAC Usage.
2.2 UAC2 information
USB Audio Class 2 (2009) additionally supports 32 bits and common rates above 96 kHz. It uses High Speed, stated as 480 MHz in the source, requiring USB 2 or 3. At 40 times Full Speed, recording 60 channels × 24 bits × 96 kHz (132 Mbit/s in the source) is described as feasible. The source describes no playback-resolution limit and backward compatibility with Class 1. OSX 10.6.4 and Linux have had Class 2 drivers since mid-2010, both supporting up to 384 kHz. Microsoft initially lacked UAC2; a Windows 10 update in April 2017 added native drivers. Older Windows requires a third-party driver. Rockchip UAC2 implements Audio Class 2.0, capture/playback without a physical sound card. Defaults: High Speed; playback/capture 48 KHz and two channels.
Bit depth: 16 bits for playback and capture. [1] Native Windows UAC2 support starts with Windows 10 version 1703. [2] Windows and Linux respond to audio events slightly differently and require compatibility handling; Linux behaves like Android. [3] Windows remembers device drivers: after configuration changes, preferably uninstall the driver so it redetects the device. [4] Kernel interfaces configure rate, channels and depth; see UAC Usage.
2.3 UAC usage
Rockchip UAC1/UAC2 configuration and functionality are largely identical; compatibility and protocol differ. Add CONFIG_USB_CONFIGFS_F_UAC1=y for UAC1 or CONFIG_USB_CONFIGFS_F_UAC2=y for UAC2 to the kernel defconfig. Linux configfs: example Kernel-4.4/4.19 script follows.
#!/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
[1] Run uac.sh restart to switch to UAC1/UAC2. [2] ${UAC} selects UAC1 or UAC2. [3] Define idProduct for the product without colliding with its other USB-function IDs. [4] Windows caches device drivers; after changing configuration, uninstall the driver for redetection. Kernel-5.10 integrates configuration in /oem/usr/bin/usb_config.sh:
[...]
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 Parameters
The Kernel-4.4/4.19 UAC1/UAC2 function directory exposes these parameter interfaces:
[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
c means capture on the USB virtual sound card, corresponding to host playback; p means virtual-card playback, corresponding to host recording. These channels are independent. Sample rate: p_srate/c_srate default to a single 48000 rate; multiple rates are comma-separated, e.g. echo 8000,16000,44100,48000 > ${UAC_GS0}/c_srate. Channel: c_chmask/p_chmask default to 3 (stereo); multiple channels or disabling a direction are supported. For a 5.1 recording device without playback: echo 0x3F > p_chmask, then echo 0 > c_chmask. Bit depth: p_ssize/c_ssize default to 2 bytes (16 bits). Volume: c_feature_unit/p_feature_unit default to 0 (off); writing 1 enables control.
UAC2 Feature Unit volume control is incompatible with Windows, so enable it for UAC1 and disable it for UAC2. req_number is the number of buffers the UAC driver submits to the USB controller. USB permits NO DATA packets when an isochronous device has no prepared data, but macOS is incompatible with this behavior. Under high CPU load, increasing req_number increases buffering and OS compatibility. The Kernel-5.10 function directory differs from 4.4/4.19 as follows:
#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
Volume/mute enable nodes change from c_feature_unit/p_feature_unit to p_mute_present/p_volume_present and c_mute_present/c_volume_present. The kernel enables volume/mute by default; the SDK uac_app need not control them by default. MIN_DB/MAX_DB/RES_DB change to -100 dB/0 dB/1 dB. Nodes p_volume_max/p_volume_min/p_volume_res and c_volume_max/c_volume_min/c_volume_res let products adapt the values to their codec. [1] Adapt uac_app so the PC slider controls codec output more linearly; see Windows Audio-Tapered Volume Controls. [2] The device reports MIN_DB/MAX_DB during enumeration; the PC maps slider 0/100 to those endpoints.
2.3.2 Uevent
For accurate audio start/stop, multiple sample rates and volume control, userspace uac_app must receive and respond to kernel events. Uevents notify userspace; monitor the uac node and extract key strings. 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
Multiple sample rates:
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
[1] IN means host recording; OUT means host playback. [2] Kernel-4.4/4.19 UAC1/UAC2 converts the raw PC volume-control value to a percentage and reports it to uac_app by uevent. [3] Kernel-5.10 reports the raw PC value directly; uvc_app (source spelling) must convert it into the codec dB value using the following reference formula:
// 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 compensation
USB timing comes from the host, whereas codec timing comes from the device. Independent clocks cause lost audio data, seen as periodic ALSA underrun/overrun messages. PPM compensation compares the host SOF packets sent every 128us (source value) with system time, calculates the PPM difference over an interval, and reports it through uevent:
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
PPM is continuously calculated while USB is connected. Userspace listens for uevent values and adjusts the codec clock through its interface. The estimate becomes more stable over time; generally no new PPM value is reported after ten minutes. A USB disconnect restarts SOF counting: PPM returns to 0 before settling to a new value. Applications without strict real-time requirements may ignore the compensation reports.
2.3.4 Compatibility
For UAC2 on Windows, disable volume control by setting c_feature_unit and p_feature_unit to 0; otherwise Windows cannot load the UAC2 driver correctly. Table 2-1: host-system support for UAC volume control.
| Windows10 | Linux(ubuntu) | MacOS | |
|---|---|---|---|
| UAC1 | Supported | Unsupported | Supported |
| UAC2 | Driver failure | Unsupported | Supported |
2.4 UAC tests
UAC1 and UAC2 use identical test procedures; UAC1 is the example. After successful configuration, connect USB to the PC. It should recognize USB Audio as shown in Figures 2-1 (Windows), 2-2 (Ubuntu output) and 2-3 (Ubuntu input).
Figure 2-1. Windows USB Audio Class 1.
Figure 2-2. Ubuntu USB Audio Class 1 output.
Figure 2-3. Ubuntu USB Audio Class 1 input. The RK3308 UART logs successful UAC1 enumeration as follows:
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
Inspect UAC1 sound-card information. In this example it is card2 (UAC1Gadget), with playback node pcmC2D0p and capture node 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 tests
Open Windows sound settings and select USB Audio as both output and input/microphone, as in Figure 2-4.
Figure 2-4. Windows audio settings. To test Windows UAC1 playback, execute the following command through RK3308 UART:
arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 | aplay -f dat -r 48000 -c 2 -D hw:0,0
The command records from Card2 (USB Audio) and plays through local Card0. Play music on Windows; RK3308 outputs it in real time. For the Windows UAC1 recording test, prepare playable audio using ADB push or arecord: 48 KHz, two channels, 16 bits.
For example, run arecord through RK3308 UART to save test.wav:
arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 /tmp/test.wav
After saving test.wav, run the UAC1 recording command:
aplay /tmp/test.wav -c 2 -r 48000 -D hw:2,0
Then use the built-in Windows Voice Recorder to save the recording, as in Figure 2-5.
Figure 2-5. Windows Voice Recorder. Alternatively, monitor the recording in real time: Sound settings → Sound Control Panel → Recording → Properties → Listen; enable Listen to this device and select the playback speaker. See Figures 2-6 and 2-7.
Figure 2-6. Windows recording monitor, step 1.
Figure 2-7. Windows recording monitor, step 2.
2.4.2 Ubuntu UAC tests
Open Ubuntu sound settings and select USB Audio as both output and input/microphone; see Figures 2-8 and 2-9.
Figure 2-8. Ubuntu audio output settings.
Figure 2-9. Ubuntu audio input settings. To test UAC1 playback, run this command through RK3308 UART:
arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 | aplay -f dat -r 48000 -c 2 -D hw:0,0
The command records Card2 (USB Audio) and plays through local Card0. Play music on Ubuntu and RK3308 outputs it in real time. For recording, prepare playable 48 KHz, two-channel, 16-bit audio using ADB push or arecord. Example: save test.wav with arecord through RK3308 UART.
arecord -f dat -t wav -r 48000 -c 2 -D hw:2,0 /tmp/test.wav
After saving test.wav, run the UAC1 recording command:
aplay /tmp/test.wav -c 2 -r 48000 -D hw:2,0
After running the command, open an Ubuntu recorder such as audacity for the test. Install audacity with:
sudo apt install audacity
Figure 2-10 shows the audacity recording interface.
Figure 2-10. Ubuntu audacity.
3. UAC1 Legacy usage and tests
3.1 UAC1 Legacy usage
Default parameter meanings: audio_buf_size is the audio buffer size, 48000; fn_cap is capture PCM /dev/snd/pcmC0D0c; fn_cntl is control device /dev/snd/controlC0; fn_play is playback PCM /dev/snd/pcmC0D0p; req_buf_size is ISO OUT request buffer size, 200; req_count is ISO OUT request count, 256.
Rockchip UAC1 Legacy implements Audio Class 1.0 but supports playback only and requires a physical sound card, default /dev/snd/pcmC0D0p. Defaults: High Speed, playback 48 KHz (not configurable), two channels (not configurable), 16 bits. Add CONFIG_USB_CONFIGFS_F_UAC1_LEGACY=y to kernel defconfig. RK3308 EVB configuration example:
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
If an ADB setup script runs at RK3308 startup, the configuration above will fail. During debugging, configure UAC1 Legacy manually with the following commands. For the final product, integrate ADB and UAC1 Legacy scripts according to requirements.
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
idProduct may be product-defined but must not collide with other USB functions. UDC is the controller name under /sys/class/udc/. Windows caches drivers; after configuration changes uninstall the driver for redetection. After successful setup, connect USB to the PC; it recognizes USB Audio as in Figure 3-1.
Figure 3-1. Windows USB Audio Class 1 Legacy. RK3308 UART log of successful enumeration:
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 exposes these configuration interfaces. Changes are not applied dynamically and must be executed in the UAC setup script.
# 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 does not create a corresponding sound-card device node on RK3308.
3.2 UAC1 Legacy tests
For PC playback settings, see the Windows or Ubuntu UAC test section. No command is needed on RK3308: after USB connection, UAC1 Legacy opens local Card0 for playback automatically.
4. Audio Source usage and tests
4.1 Audio Source usage
Rockchip Audio Source implements Audio Class 1.0 but supports recording only. Defaults: High Speed; playback rate 44.1 KHz, with the following 15 rates dynamically configurable by the PC.
8000, 11025, 16000, 22050, 24000,
32000, 40000, 44100, 48000, 56000,
64000, 72000, 80000, 88200, 96000,
Playback has two channels (not configurable) and 16-bit depth. Add CONFIG_USB_CONFIGFS_F_ACC=y, required by Audio Source, and CONFIG_USB_CONFIGFS_F_AUDIO_SRC=y to kernel defconfig.
RK3308 EVB Audio Source configuration example:
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
If RK3308 starts an ADB configuration script automatically, the setup above fails. For debugging, configure Audio Source manually with the commands below. Integrate ADB and Audio Source scripts appropriately for the final product.
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
idProduct may be product-defined without conflicting with other USB functions. UDC is the controller name under /sys/class/udc/. After changes, uninstall cached Windows drivers to redetect the device. Once configured, connect USB: the PC recognizes USB Audio as in Figures 4-1 and 4-2.
Figure 4-1. Windows USB Audio Source.
Figure 4-2. Ubuntu USB Audio Source. RK3308 UART log of normal Audio Source enumeration:
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 exposes no configurable kernel interfaces. Inspect its information as follows: the example is card2 (audiosource), with only playback node 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 tests
For Audio Source recording, use the Windows or Ubuntu recording settings described earlier. RK3308 test command, assuming the default 44.1 KHz:
aplay /tmp/test.wav -r 44100 -c 2 -D hw:2,0
test.wav must have the same sample rate as the recording; otherwise noise or silence may result. The PC can dynamically select among 15 rates: Sound settings → Sound Control Panel → Recording → Properties → Advanced, then choose the rate (Figure 4-3).
Figure 4-3. Windows USB Audio Source settings.
5. UAC1 Legacy and Audio Source composite usage and tests
5.1 Composite-device usage
UAC1 Legacy and Audio Source can form one composite USB device with recording and playback. Add CONFIG_USB_CONFIGFS_F_UAC1_LEGACY=y, CONFIG_USB_CONFIGFS_F_ACC=y (Audio Source dependency), and CONFIG_USB_CONFIGFS_F_AUDIO_SRC=y to kernel defconfig. Also apply support_uac1_legacy_and_audio_source.patch separately. Example RK3308 EVB composite setup:
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
For other setup and debugging methods, see UAC1 Legacy Usage and Audio Source Usage.
5.2 Composite-device tests
See UAC1 Legacy Test and Audio Source Test.
6. References
USB protocols from USB-IF:
- Universal Serial Bus Specification, Revision 2.0
- Universal Serial Bus Audio Device Class Specification for Basic Audio Devices
- Universal Serial Bus Device Class Definition for Audio Devices, Release 1.0
- Universal Serial Bus Device Class Definition for Audio Devices, Release 2.0
- Universal Serial Bus Device Class Definition for Audio Data Formats (USB Audio Data Formats)
- Universal Serial Bus Device Class Definition for Terminal Types (USB Audio Terminal Types)
Other references:
- The Well-Tempered Computer (An introduction to computer audio) — USB
- Windows USB Audio 2.0 Drivers
- Windows Audio-Tapered Volume Controls
7. Appendix A: UAC1 device descriptor
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. Appendix B: UAC2 device descriptor
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)