I know that there are already some questions which are similar to mine but they are old and doesn't helped me. I'm very new with libusb but I already come to the point where I get the libusb_device_handle. The Problem is that I don't know what the next step is. One part of my program is to capture audio from my FM radio stick. This stick sends audio over usb and has also an interface to change the frequency and so on.
With windows the stick is recognized as audio input device and I'm able to listen to that. My program should run on android 4.2 and above but my smartphone on which I want test my app does not support audio input devices over usb therefore I want to get it working with libusb.
The libusb -v command on Ubuntu looks like this:
Bus 002 Device 007: ID 10c4:818a Cygnal Integrated Products, Inc. Silicon Labs FM Radio Reference Design
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 1.10
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x10c4 Cygnal Integrated Products, Inc.
idProduct 0x818a Silicon Labs FM Radio Reference Design
bcdDevice 1.00
iManufacturer 1 SILICON LABORATORIES INC.
iProduct 2 FM Radio
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 145
bNumInterfaces 3
bConfigurationValue 1
iConfiguration 0
bmAttributes 0x80
(Bus Powered)
MaxPower 100mA
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 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 1.00
wTotalLength 43
bInCollection 1
baInterfaceNr( 0) 1
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 1
wTerminalType 0x0710 Radio Receiver
bAssocTerminal 0
bNrChannels 2
wChannelConfig 0x0003
Left Front (L)
Right Front (R)
iChannelNames 0
iTerminal 0
AudioControl Interface Descriptor:
bLength 13
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 2
bSourceID 1
bControlSize 2
bmaControls( 0) 0x01
bmaControls( 0) 0x00
Mute Control
bmaControls( 1) 0x00
bmaControls( 1) 0x00
bmaControls( 2) 0x00
bmaControls( 2) 0x00
iFeature 0
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 3
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bSourceID 2
iTerminal 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 3
bDelay 0 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] 96000
Endpoint Descriptor:
bLength 9
bDescriptorType 5
bEndpointAddress 0x83 EP 3 IN
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0200 1x 512 bytes
bInterval 1
bRefresh 0
bSynchAddress 0
AudioControl Endpoint Descriptor:
bLength 7
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bLockDelayUnits 2 Decoded PCM samples
wLockDelay 0 Decoded PCM samples
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 2
bInterfaceClass 3 Human Interface Device
bInterfaceSubClass 0 No Subclass
bInterfaceProtocol 0 None
iInterface 0
HID Device Descriptor:
bLength 9
bDescriptorType 33
bcdHID 1.11
bCountryCode 0 Not supported
bNumDescriptors 1
bDescriptorType 34 Report
wDescriptorLength 203
Report Descriptors:
** UNAVAILABLE **
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 10
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0040 1x 64 bytes
bInterval 1
Device Status: 0x0000
(Bus Powered)
If it helps the source code of that radio stick is open source and can be downloaded.
Please can somebody tell me what I have to do after libusb_open2 to capture the audio and write it to an file
Edited 28.08.2014:
So, I'm now able to get data from my audio stick but I think there is something wrong.
I'm allocation 10 libusb_transfer objects with 10 iso packets for each transfer.
The callback function will be called and I checked the actual_length from the libusb_iso_packet_descriptor object. The packet size is 512 but the actual_length is between 380 and 382.
To check if the data is correct I'm also stopping the time between the first and the last callback. If I stop the transfer the sum of libusb_iso_packet_descriptor->length is too big and the sum of libusb_iso_packet_descriptor->actual_length is to low.
Thanks Thomas
