How to get USB Audio on Android 6 with IMX6?

[mmaitland]

Hi,

I am trying to enable support for USB Audio on Android 6 using the tinyalsa HAL.

This is what I have done so far:

I have verified that the device exists in /proc/asound/devices:

     9: [ 3- 0]: digital audio playback
    10: [ 3- 0]: digital audio capture

In /proc/asound/devices/card3, I verified that the device supported playback. Here is the contents of stream0 to show this:

Creative Technology Ltd Sound Blaster Play! 3 at usb-ci_hdrc.1-1.2, full speed : USB Audio

Playback:
  Status: Stop
  Interface 1
    Altset 1
    Format: S16_LE
    Channels: 2
    Endpoint: 1 OUT (SYNC)
    Rates: 44100, 48000
  Interface 1
    Altset 2
    Format: S24_3LE
    Channels: 2
    Endpoint: 1 OUT (SYNC)
    Rates: 44100, 48000
  Interface 1
    Altset 3
    Format: S16_LE
    Channels: 2
    Endpoint: 1 OUT (SYNC)
    Rates: 88200, 96000
  Interface 1
    Altset 4
    Format: S24_3LE
    Channels: 2
    Endpoint: 1 OUT (SYNC)
    Rates: 88200, 96000

I have added USB audio to my audio_policy.conf:

usb {     outputs {       usb_accessory {         sampling_rates 44100         channel_masks AUDIO_CHANNEL_OUT_STEREO         formats AUDIO_FORMAT_PCM_16_BIT         devices AUDIO_DEVICE_OUT_USB_ACCESSORY       }       usb_device {         sampling_rates 44100         channel_masks AUDIO_CHANNEL_OUT_STEREO         formats AUDIO_FORMAT_PCM_16_BIT         devices AUDIO_DEVICE_OUT_USB_DEVICE       }     }   }


With regard to the alsa setup, this was the existing config_usbaudio.h

/* ALSA cards for IMX, these must be defined according different board / kernel config*/
static struct audio_card  usbaudio_card = {
    .name = "USB Device",
    .driver_name = "USB-Audio",
    .supported_out_devices  = AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET,
    .supported_in_devices   = AUDIO_DEVICE_IN_USB_DEVICE|AUDIO_DEVICE_IN_DGTL_DOCK_HEADSET,
    .defaults            = NULL,
    .bt_output           = NULL,
    .speaker_output      = NULL,
    .hs_output           = NULL,
    .earpiece_output     = NULL,
    .vx_hs_mic_input     = NULL,
    .mm_main_mic_input   = NULL,
    .vx_main_mic_input   = NULL,
    .mm_hs_mic_input     = NULL,
    .vx_bt_mic_input     = NULL,
    .mm_bt_mic_input     = NULL,
    .card                = 0,
    .out_rate            = 0,
    .out_channels        = 0,
    .out_format          = 0,
    .in_rate             = 0,
    .in_channels         = 0,
    .in_format           = 0,
};

I'm not sure if I have to change any of this and would appreciate some direction with what I must do with this file.

In tinyalsa_hal.c I added the usbaudio_card above to the supported devices:

/*"null_card" must be in the end of this array*/
struct audio_card *audio_card_list[] = {
    &wm8958_card,
    &wm8962_card,
    &hdmi_card,
    &spdif_card,
    &cs42888_card,
    &wm8960_card,
    &sii902x_card,
    &sgtl5000_card,
    &tc358743_card,
    &usbaudio_card,
    &null_card,
};

Lastly, I ran tinyhal test.wav -D 3 -d 0 and did not have any errors but no sound came out. Note that I ran this before making all of the above changes. (It should not be affected by the audio policy but I will update if this ends up working once I compile the tinyhal additions)

On android, the USB device is seen but does not use the alsa hal:
01-01 00:00:49.924 2359-2359/? I/AudioFlinger: loadHwModule() Loaded primary audio interface from Freescale i.MX Audio HW HAL (audio) handle 1
01-01 00:00:49.927 2359-2359/? I/AudioFlinger: loadHwModule() Loaded usb audio interface from USB audio HW HAL (audio) handle 2
01-01 00:00:49.927 2359-2359/? I/AudioFlinger: openOutput(), module 2 Device 4000, SamplingRate 0, Format 00000000, Channels 0, flags 0
01-01 00:00:49.927 2359-2359/? I/AudioFlinger: AudioStreamOut::open(), mHalFormatIsLinearPcm = 1
01-01 00:00:49.928 2359-2359/? I/AudioFlinger: HAL output buffer size 448 frames, normal sink buffer size 896 frames

Even with this no sound comes out

My questions are, what else must I do to get usb audio working on android? How do I enable the use of tinyhal on android? Am I doing anything wrong? Is there any documentation you could point me to because the android source documentation on audio almost leaves out android 6 completely.

Thanks in advance for the help 

[weidong_sun]

Hello Michael,

Information below are from android design team:

-----------------------

usb audo HAL is AOSP code, no related to  our audio HAL, so USB sound card can be used directly.

----------------------

In addition, The descriptions on USB Audio here should be helpful for your application:

USB Digital Audio  |  Android Open Source Project 

Have a nice day!

B.R,

Weidong