This article provides how to use the USB 2.0 Gadget Audio on SP7350 board which makes the board as an audio card.

Hardware Configuration

Item 13 : USB 2.0 Type A

Item 14 : USB 2.0 Micro-AB

Item 15 : USB 3.0 Type C

Kernel Setup

Enter kernel configuration

# cd ./linux/kernel
# make menuconfig

1. Select submenus : Device Drivers > Sound card support > Advances Linux Sound Architecture. Select [*] for “PCM timer interface“.

2. Select submenus : Device Drivers > Sound card support > Advances Linux Sound Architecture > USB sound devices. Select <*> for “USB Audio/MIDI driver“.

3. Select submenus : Device Drivers > USB support > USB support > USB Gadget Support > USB Peripheral Controller. Select <*> for “Sunplus USB 2.0 Device Controller“.

4. Select submenus : Device Drivers > USB support > USB support > USB Gadget Support. Select <*> for “USB Gadget functions configurable through configfs“, [*] for “Function filesystem (FunctionFS)” and [*] for “Audio Class 1.0“.

ConfigFS

Configure UAC gadget through configfs saved as a file named setup_uac.

#!/bin/sh

CONFIGFS_HOME=/sys/kernel/config
VID=0xabcd
PID=0x1234
serial_number="myserial"
manufacturer="mymfg"
product="myproduct"
name="c"
number="1"
configuration="uac1"
maxpower="500"

CONFIG="configs/$name.$number"
FUNCTION="uac1.0"
UDC_NAME="f8102800.usb"

modprobe libcomposite

mount -t configfs none $CONFIGFS_HOME
mkdir -p $CONFIGFS_HOME/usb_gadget/g1
cd $CONFIGFS_HOME/usb_gadget/g1
echo $VID > idVendor
echo $PID > idProduct

mkdir -p strings/0x409
echo $serial_number > strings/0x409/serialnumber
echo $manufacturer > strings/0x409/manufacturer
echo $product > strings/0x409/product

mkdir -p configs/$name.$number
echo $maxpower > configs/$name.$number/MaxPower

mkdir -p configs/$name.$number/strings/0x409
echo $configuration > configs/$name.$number/strings/0x409/configuration

mkdir -p functions/$FUNCTION
echo 0x3 > functions/$FUNCTION/p_chmask
echo 48000 > functions/$FUNCTION/p_srate
echo 2 > functions/$FUNCTION/p_ssize
echo 0x3 > functions/$FUNCTION/c_chmask
echo 48000 > functions/$FUNCTION/c_srate
echo 2 > functions/$FUNCTION/c_ssize

ln -s functions/$FUNCTION configs/$name.$number
echo $UDC_NAME > UDC

Test Configurations

1. Use an USB-A to Micro-USB cable to connect the Windows PC and the SP7350 platform.

2. Plug an USB sound card to the USB 3.0 Type C port of the SP7350 platform and plug a earphone to the sound card.

3. Use sudo sh setup_uac command to configure UDC (USB 2.0) as an UAC gadget.

sunplus@ubuntu:~$ sudo sh setup_uac
[sudo] password for sunplus:
sunplus@ubuntu:~$

4. Use cat /proc/asound/cards command to show all sound cards of the SP7350 platform. The sound cards of 1 [UAC1Gadget] and 2 [Device] will be used for the test.

sunplus@ubuntu:~$ cat /proc/asound/cards
 0 [spaud          ]: sp-aud - sp-aud
                      Q645/Q654, Sunplus Technology Inc.
 1 [UAC1Gadget     ]: UAC1_Gadget - UAC1_Gadget
                      UAC1_Gadget 0
 2 [Device         ]: USB-Audio - USB Audio Device
                      C-Media Electronics Inc. USB Audio Device at usb-xhci-hcd.1.auto-1, full speed
sunplus@ubuntu:~$

In Device Manager of Windows PC, “Capture Input terminal (AC Interface)“ and “Speakers (AC Interface)“ will show up in Audio inputs and outputs. “AC Interface” will show up in Sound, video and game controllers.

Test

Record and Play

Play music and choose “Speakers (AC Interface)“ in Windows PC. Then use arecord -D hw:1,0 -c 2 -r 48000 -f S16_LE | aplay -D hw:2,0 -c 2 -r 48000 -f S16_LE command to output the sounds to the earphone of the USB sound card in USB 3.0 type C port in the SP7350 platform.

sunplus@ubuntu:~$ arecord -D hw:1,0 -c 2 -r 48000 -f S16_LE | aplay -D hw:2,0 -c 2 -r 48000 -f S16_LE
Recording WAVE 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo

Record Channel

Play music and choose “Speakers (AC Interface)“ in Windows PC. Then use arecord -D hw:1,0 -c 2 -r 48000 -f S16_LE pc_music.wav command to record it as pc_music.wav in the SP7350 platform.

sunplus@ubuntu:~$ arecord -D hw:1,0 -c 2 -r 48000 -f S16_LE pc_music.wav
Recording WAVE 'pc_music.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo

Play Channel

Use aplay -D hw:1,0 -c 2 -r 48000 -f S16_LE pc_music.wav command to play pc_music.wav in the SP7350 platform. Then choose “Capture Input terminal (AC Interface)“ and record it in the Windows PC.

sunplus@ubuntu:~$ aplay -D hw:1,0 -c 2 -r 48000 -f S16_LE pc_music.wav
Playing WAVE 'pc_music.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo