As a USB sound card¶

By the default, the micro USB port of the Nanopi Neo Air is used as a serial port. While it can also be used a USB sound card.

1. rm g_serial from the file /etc/module and reboot.

2. run the script to setup a USB Audio Class 1.0 (UAC1) device

   #!/bin/bash
   modprobe libcomposite
   mkdir -p /sys/kernel/config/usb_gadget/g
   echo 0x1d6b > /sys/kernel/config/usb_gadget/g/idVendor  # Linux Foundation
   echo 0x0104 > /sys/kernel/config/usb_gadget/g/idProduct # Multifunction Composite Gadget
   echo 0x0100 > /sys/kernel/config/usb_gadget/g/bcdDevice # v1.0.0
   echo 0x0200 > /sys/kernel/config/usb_gadget/g/bcdUSB    # USB 2.0
   echo 0xef > /sys/kernel/config/usb_gadget/g/bDeviceClass    # USB 2.0
   echo 0x02 > /sys/kernel/config/usb_gadget/g/bDeviceSubClass # USB 2.0
   echo 0x01 > /sys/kernel/config/usb_gadget/g/bDeviceProtocol # USB 2.0
   mkdir -p  /sys/kernel/config/usb_gadget/g/strings/0x409
   echo "000001" > /sys/kernel/config/usb_gadget/g/strings/0x409/serialnumber
   echo "VOICEN" > /sys/kernel/config/usb_gadget/g/strings/0x409/manufacturer
   echo "devkit" > /sys/kernel/config/usb_gadget/g/strings/0x409/product
   mkdir -p /sys/kernel/config/usb_gadget/g/functions/uac1.usb0   # audio
   echo 0x1 > /sys/kernel/config/usb_gadget/g/functions/uac1.usb0/c_chmask
   echo 48000 > /sys/kernel/config/usb_gadget/g/functions/uac1.usb0/c_srate
   echo 0xf > /sys/kernel/config/usb_gadget/g/functions/uac1.usb0/p_chmask
   echo 16000 > /sys/kernel/config/usb_gadget/g/functions/uac1.usb0/p_srate
   mkdir -p /sys/kernel/config/usb_gadget/g/configs/c.1
   echo 250 > /sys/kernel/config/usb_gadget/g/configs/c.1/MaxPower
   ln -s /sys/kernel/config/usb_gadget/g/functions/uac1.usb0  /sys/kernel/config/usb_gadget/g/configs/c.1/
   udevadm settle -t 5 || :
   ls /sys/class/udc/ > /sys/kernel/config/usb_gadget/g/UDC
   

3. run aplay -l and areocrd -l to check the virtual capture/playback devices created by the script

   $ aplay -l
   **** List of PLAYBACK Hardware Devices ****
   card 0: Codec [H3 Audio Codec], device 0: CDC PCM Codec-0 []
   Subdevices: 1/1
   Subdevice #0: subdevice #0
   card 2: UAC1Gadget [UAC1_Gadget], device 0: UAC1_PCM [UAC1_PCM]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
   $ arecord -l
   **** List of CAPTURE Hardware Devices ****
   card 0: Codec [H3 Audio Codec], device 0: CDC PCM Codec-0 []
   Subdevices: 1/1
   Subdevice #0: subdevice #0
   card 1: voicen4mic [voicen4mic], device 0: 1c22000.i2s-ac108-codec0 ac108-codec.0-003b-0 []
   Subdevices: 1/1
   Subdevice #0: subdevice #0
   card 2: UAC1Gadget [UAC1_Gadget], device 0: UAC1_PCM [UAC1_PCM]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
   

4. when playing an audio through the USB sound card on a computer, the audio is sent to the capture device hw:UAC1Gadget, and then run arecord -f S16_LE -c 1 -r 48000 -D hw:UAC1Gadget | aplay to play the audio on the device.

5. when recording through the sound card on the computer, data is sent from the playback device hw:UAC1Gadget to the computer.

   a. use Audacity to record audio on a computer.

   To reocrd 4 (more than 2) channels audio, Windows WASAPI is selected

   

   b. run arecord -f S16_LE -c 4 -r 16000 | aplay -D hw:UAC1Gadget to send microphone data to the computer.