How do I set the usb audio code up for usb asynchronous transfers.
Do I just have to change bmAttributes
USB_ENDPOINT_TYPE_ISOCHRONOUS,
to
USB_ENDPOINT_SYNC_ASYNCHRONOUS
or is it more complexed than that.
What "usb audio code" ?
This code, I have looked and looked can't not seem to find much support on this subject, asynchronous transfers.
http://www.keil.com/download/files/lpc2368_usbaudio.zip
Here is a descriptor readout of a typical Async Sink device (Ayre QB9), taken from list.voyage.hk/.../013449.html
Compare it with the example's
lsusb -v Bus 001 Device 004: ID 21b4:0130 Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.00 bDeviceClass 0 (Defined at Interface level) bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 idVendor 0x21b4 idProduct 0x0130 bcdDevice 1.71 iManufacturer 1 iProduct 2 iSerial 3 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 134 bNumInterfaces 3 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 7 AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 1 (HEADER) bcdADC 1.00 wTotalLength 30 bInCollection 1 baInterfaceNr( 0) 1 AudioControl Interface Descriptor: bLength 12 bDescriptorType 36 bDescriptorSubtype 2 (INPUT_TERMINAL) bTerminalID 1 wTerminalType 0x0101 USB Streaming 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 6 wTerminalType 0x0301 Speaker bAssocTerminal 0 bSourceID 1 iTerminal 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 9 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 1 bNumEndpoints 2 bInterfaceClass 1 Audio bInterfaceSubClass 2 Streaming bInterfaceProtocol 0 iInterface 8 AudioStreaming Interface Descriptor: bLength 7 bDescriptorType 36 bDescriptorSubtype 1 (AS_GENERAL) bTerminalLink 1 bDelay 1 frames wFormatTag 1 PCM AudioStreaming Interface Descriptor: bLength 20 bDescriptorType 36 bDescriptorSubtype 2 (FORMAT_TYPE) bFormatType 1 (FORMAT_TYPE_I) bNrChannels 2 bSubframeSize 3 bBitResolution 24 bSamFreqType 4 Discrete tSamFreq[ 0] 44100 tSamFreq[ 1] 48000 tSamFreq[ 2] 88200 tSamFreq[ 3] 96000 Endpoint Descriptor: bLength 9 bDescriptorType 5 bEndpointAddress 0x01 EP 1 OUT bmAttributes 5 Transfer Type Isochronous Synch Type Asynchronous Usage Type Data wMaxPacketSize 0x0246 1x 582 bytes bInterval 1 bRefresh 0 bSynchAddress 129 AudioControl Endpoint Descriptor: bLength 7 bDescriptorType 37 bDescriptorSubtype 1 (EP_GENERAL) bmAttributes 0x01 Sampling Frequency bLockDelayUnits 2 Decoded PCM samples wLockDelay 0 Decoded PCM samples Endpoint Descriptor: bLength 9 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 1 Transfer Type Isochronous Synch Type None Usage Type Data wMaxPacketSize 0x0003 1x 3 bytes bInterval 1 bRefresh 1 bSynchAddress 0 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 2 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 254 Application Specific Interface bInterfaceSubClass 1 Device Firmware Update bInterfaceProtocol 0 iInterface 14 Device Firmware Upgrade Interface Descriptor: bLength 7 bDescriptorType 33 bmAttributes 7 Will Not Detach Manifestation Tolerant Upload Supported Download Supported wDetachTimeout 250 milliseconds wTransferSize 64 bytes
Tsuneo
The terms, Asynchronous / Synchronous / Adaptive on USB audio class mean the synchronization type. It suggests the place where the original sampling clock sits on.
- Asynchronous: the sampling clock is generated on the device side. - Synchronous: the clock derives from USB SOF by PLL - Adaptive: the clock is generated on the host side.
For Asynchronous Sink (output) device, like a speaker, the device has to notify to host on its sampling clock, to synchronize the host. For this purpose, a feedback endpoint (isoc IN) is associated to the isoc OUT endpoint of the audio stream, like above QB9
For Asynchronous Source (input) device, like a microphone, The sampling rate on the device is shown as the number of the samples in each isoc packet on the audio stream. The number is relative to the SOF frequency. Therefore, any feedback endpoint is not required.
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