Hi All,

I am trying to playback audio from Android phone using USB AOAv2. (PCM audio, 16bit, 44.1 KHz, stereo) on a Wandboard Quad (i.MX6) board running Ubuntu 14.04.

The detection of phone is fine and playback via alsa commands/gstreamer is successful. But during playback, there are distortions in the sound.

dmesg prints as follows, retire_capture_urb: x callbacks suppressed ----->[x is around 41 to 300] retire_capture_urb: x callbacks suppressed retire_capture_urb: x callbacks suppressed retire_capture_urb: x callbacks suppressed

arecord command prints underrun occurred.

So each time, retire_capture_urb is printed, there is a distortion.

I tried the same program on different machines. Following are the results, On Wandboard, the distortions happen each 40 seconds or so. On a Linux server PC running Ubuntu 14.04 the audio breaks are more frequent. On a Linux PC running Ubuntu 12.02 the audio breaks are less frequent.

Could anyone guide me on how retire_capture_urb be prevented or how can a smooth playback be achieved ?

Should there be any special configurations done at USB driver ?

lsusb -v print is as follows, The synch type for the endpoint appears to be enumerated as Synchronous. Could the synch type be modified using libusb, is this the cause of underrun?

Bus 001 Device 004: ID 18d1:2d02 Google Inc. Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 2.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 idVendor 0x18d1 Google Inc. idProduct 0x2d02 bcdDevice ff.ff iManufacturer 1 motorola iProduct 2 MotoG3-TE iSerial 3 ZY222WB7TT bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 110 bNumInterfaces 2 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x80 (Bus Powered) MaxPower 500mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 1 Control Device bInterfaceProtocol 0 iInterface 0 AudioControl Interface Descriptor: bLength 10 bDescriptorType 36 bDescriptorSubtype 1 (HEADER) bcdADC 1.00 wTotalLength 40 bInCollection 2 baInterfaceNr( 0) 0 baInterfaceNr( 1) 1 AudioControl Interface Descriptor: bLength 12 bDescriptorType 36 bDescriptorSubtype 2 (INPUT_TERMINAL) bTerminalID 1 wTerminalType 0x0201 Microphone bAssocTerminal 0 bNrChannels 2 wChannelConfig 0x0003 Left Front (L) Right Front (R) iChannelNames 0 iTerminal 0 AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 3 (OUTPUT_TERMINAL) bTerminalID 3 wTerminalType 0x0101 USB Streaming bAssocTerminal 2 bSourceID 2 iTerminal 0 AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 6 (FEATURE_UNIT) bUnitID 2 bSourceID 1 bControlSize 2 bmaControls( 0) 0x00 bmaControls( 0) 0x00 iFeature 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 1 bNumEndpoints 1 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 0 AudioStreaming Interface Descriptor: bLength 7 bDescriptorType 36 bDescriptorSubtype 1 (AS_GENERAL) bTerminalLink 1 bDelay 1 frames wFormatTag 1 PCM AudioStreaming Interface Descriptor: bLength 11 bDescriptorType 36 bDescriptorSubtype 2 (FORMAT_TYPE) bFormatType 1 (FORMAT_TYPE_I) bNrChannels 2 bSubframeSize 2 bBitResolution 16 bSamFreqType 1 Discrete tSamFreq[ 0] 44100 Endpoint Descriptor: bLength 9 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 13 Transfer Type Isochronous Synch Type Synchronous Usage Type Data wMaxPacketSize 0x0100 1x 256 bytes bInterval 4 bRefresh 0 bSynchAddress 0 AudioControl Endpoint Descriptor: bLength 7 bDescriptorType 37 bDescriptorSubtype 1 (EP_GENERAL) bmAttributes 0x01 Sampling Frequency bLockDelayUnits 1 Milliseconds wLockDelay 1 Milliseconds Device Qualifier (for other device speed): bLength 10 bDescriptorType 6 bcdUSB 2.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 bNumConfigurations 1 Device Status: 0x0000 (Bus Powered)

Thanks for the help..