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

Table of Contents

Kernel Setup

Enter the kernel configuration by running the following command in the top directory of project.

# cd ./linux/kernel
# make menuconfigkconfig

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

...

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

...

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

...

4. Select submenus for USB 3.0 controller : Device Drivers > USB support. Select <*> for “DesignWare USB3 DRD Core Support“ and select “Dual Role mode“ for “Deware USB3 DRD Core Support“.

...

5. Select submenus for USB Gadget configfs : Device Drivers > USB support > USB Gadget Support. Select <*> for “USB Gadget functions configurable through configfs“

...

5. and [*] for “Audio Class 1.0“ and “Audio Class 2.0“.

...

ConfigFS

Configure the UAC gadget through configfs saved as a file named setup_uac. It configures USB 2.0 as an UAC 1.0 gadget by default.

#!/bin/sh

# USB2 or USB3
AUDIO_EN=USB2

# 1.0 or 2.0
AUDIO_CLASS_VERSION=2.0

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

if [ $AUDIO_CLASS_VERSION = 1.0 ]
then
        configuration="uac1"
maxpower="500"


elif [ $AUDIO_CLASS_VERSION = 2.0 ]
then
        configuration="uac2"
fi

CONFIG="configs/$name.$number"

if [ $AUDIO_CLASS_VERSION = 1.0 ]
then
        FUNCTION="uac1.0"
elif [ $AUDIO_CLASS_VERSION = 2.0 ]
then
        FUNCTION="uac2.0"
fi

if [ $AUDIO_EN = USB2 ]
then
        UDC_NAME="f8102800.usb"

        # disable debug message
        echo 0 > /sys/module/sunplus_udc/parameters/dmsg
elif [ $AUDIO_EN = USB3 ]
then
        UDC_NAME="f80a1000.dwc3"
fi

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 for USB 2.0 Gadget Audio

1. Use an USB-A to Micro-USB cable to connect the Windows Ubuntu 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 1.0 gadget.

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

...

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 Windows PC, “AC Interface” of “Sound, video and game controllers” will show up in Device Manager.

...

Test

Record and Play

...

the Ubuntu PC, “Digital Output (S/PDIF) - UDisk flash drive“ and “Analog Output - UDisk flash drive“ will show up in “Settings“ → “Sound” → “Output” → “Output Device”. “Digital Input (S/PDIF) - UDisk flash drive“ and “Analog Input - UDisk flash drive“ will show up in “Settings“ → “Sound” → “Input” → “Input Device”.

...

Test for USB 2.0 Gadget Audio

The command-line audio player (aplay) and soundfile recorder (arecord) are used for the test.

Record and Play

...

Play music and choose “Digital Output (S/PDIF) - UDisk flash drive“ or “Analog Output - UDisk flash drive“ in the Ubuntu 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 record the music from the UAC gadget and play it 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 in Windows PC and and choose “Digital Output (S/PDIF) - UDisk flash drive“ or “Analog Output - UDisk flash drive“ in the Ubuntu 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 UAC gadget.

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 “Digital Input (S/PDIF) - UDisk flash drive“ or “Analog Input - UDisk flash drive“ and record it in the Windows Ubuntu 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