USB Gadget Audio Example

Introduction

This page provides a guide on how to use the USB Gadget Audio on ADSP-SC5XX boards. It provides the capability for the board to be used (and appear to Host PCs) as an audio card.

📝	The USB Gadget Audio feature can be enabled when following the Getting Started Guides (version 3.0.0 or later). You need to append the following line to the conf/local.conf file - DISTRO_FEATURES:append = “ adi_usb_gadget_audio” - before building the image.

Hardware Configuration

Connect the USB micro-B plug cable into the USB HS/OTG Device port, as showing below:

Usage

Capture and Play on-board

Type the following into the target board:

root@adsp-sc589-mini:~# ls /dev/snd/
by-path  controlC0  controlC1  pcmC0D0c  pcmC0D0p  pcmC1D0c  pcmC1D0p  timer
root@adsp-sc589-mini:~# modprobe g_audio c_srate=48000
g_audio gadget: Linux USB Audio Gadget, version: Feb 2, 2012
g_audio gadget: g_audio ready

A new sound card UAC2Gadget is generated both for playback and capture on the EZ-KIT board:

root@adsp-sc589-mini:~# arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: sc5xxasoccard [sc5xx-asoc-card], device 0: adau1761 adau-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: UAC2Gadget [UAC2_Gadget], device 0: UAC2 PCM [UAC2 PCM]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
root@adsp-sc589-mini:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: sc5xxasoccard [sc5xx-asoc-card], device 0: adau1761 adau-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: UAC2Gadget [UAC2_Gadget], device 0: UAC2 PCM [UAC2 PCM]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Record audio data from the new generated UAC2 sound card (arecord card 1, device 0) and play the recorded data via normal playback device (aplay card 0, device 1)

root@adsp-sc589-mini:~# arecord -f dat -t wav -D hw:1,0 -c 2 -r 48000 -f S16_LE |aplay -D hw:0,0
Recording WAVE 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
Playing WAVE 'stdin' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo

Play audio over USB on Host

With following command you should be able to see the USB Gadget Audio device is there on your host PC:

test@madara:~$ lsusb
Bus 002 Device 033: ID 1d6b:0101 Linux Foundation Audio Gadget

Then, list the available sound card on host PC, to decide which sound card is associated with the EZ-KIT board

test@madara:~$ cat /proc/asound/cards
 0 [PCH            ]: HDA-Intel - HDA Intel PCH
                      HDA Intel PCH at 0xf7d00000 irq 28
 1 [Gadget         ]: USB-Audio - Linux USB Audio Gadget
                      Linux 4.19.0-yocto-standard with musb-hdrc Linux USB Audio Gadget at usb-0000:0

test@madara:~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: CX20641 Analog [CX20641 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Gadget [Linux USB Audio Gadget], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
test@madara:~$ arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: CX20641 Analog [CX20641 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 2: CX20641 Alt Analog [CX20641 Alt Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Gadget [Linux USB Audio Gadget], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

USB Audio Gadget is the sound card 1 (aplay card 1, device 0).

We can play an audio file:

test@madara:~$ aplay -D hw:1,0 sample_s16_le.wav
Playing WAVE 'sample_s16_le.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo

and hear the music playing out from the headset.