Hm, I do not remember any issues with the feedback EP IN bInterval=4 on Win10 from the current linux gadget. Quite a few people use it, combined with CamillaDSP.
lsusb -v (descriptor dump):
The way the linux host driver views the device:
lsusb -v (descriptor dump):
Code:
Bus 001 Device 006: ID 1d6b:0101 Linux Foundation Audio Gadget
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.01
bDeviceClass 239 Miscellaneous Device
bDeviceSubClass 2
bDeviceProtocol 1 Interface Association
bMaxPacketSize0 64
idVendor 0x1d6b Linux Foundation
idProduct 0x0101 Audio Gadget
bcdDevice 6.01
iManufacturer 1
iProduct 2
iSerial 0
bNumConfigurations 1
Configuration Descriptor:
bLength 9
bDescriptorType 2
wTotalLength 0x010d
bNumInterfaces 3
bConfigurationValue 1
iConfiguration 0
bmAttributes 0xc0
Self Powered
MaxPower 0mA
Interface Association:
bLength 8
bDescriptorType 11
bFirstInterface 0
bInterfaceCount 3
bFunctionClass 1 Audio
bFunctionSubClass 0
bFunctionProtocol 32
iFunction 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 0
bAlternateSetting 0
bNumEndpoints 1
bInterfaceClass 1 Audio
bInterfaceSubClass 1 Control Device
bInterfaceProtocol 32
iInterface 5
AudioControl Interface Descriptor:
bLength 9
bDescriptorType 36
bDescriptorSubtype 1 (HEADER)
bcdADC 2.00
bCategory 8
wTotalLength 0x0077
bmControls 0x00
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 8
bmAttributes 1 Internal fixed clock
bmControls 0x03
Clock Frequency Control (read/write)
bAssocTerminal 0
iClockSource 6
AudioControl Interface Descriptor:
bLength 8
bDescriptorType 36
bDescriptorSubtype 10 (CLOCK_SOURCE)
bClockID 7
bmAttributes 1 Internal fixed clock
bmControls 0x03
Clock Frequency Control (read/write)
bAssocTerminal 0
iClockSource 7
AudioControl Interface Descriptor:
bLength 17
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 1
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bCSourceID 7
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
iChannelNames 0
bmControls 0x0003
Copy Protect Control (read/write)
iTerminal 8
AudioControl Interface Descriptor:
bLength 18
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 5
bSourceID 1
bmaControls(0) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
bmaControls(1) 0x00000000
bmaControls(2) 0x00000000
iFeature 13
AudioControl Interface Descriptor:
bLength 17
bDescriptorType 36
bDescriptorSubtype 2 (INPUT_TERMINAL)
bTerminalID 2
wTerminalType 0x0201 Microphone
bAssocTerminal 0
bCSourceID 8
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
iChannelNames 0
bmControls 0x0003
Copy Protect Control (read/write)
iTerminal 9
AudioControl Interface Descriptor:
bLength 18
bDescriptorType 36
bDescriptorSubtype 6 (FEATURE_UNIT)
bUnitID 6
bSourceID 2
bmaControls(0) 0x0000000f
Mute Control (read/write)
Volume Control (read/write)
bmaControls(1) 0x00000000
bmaControls(2) 0x00000000
iFeature 12
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 4
wTerminalType 0x0101 USB Streaming
bAssocTerminal 0
bSourceID 6
bCSourceID 8
bmControls 0x0003
Copy Protect Control (read/write)
iTerminal 10
AudioControl Interface Descriptor:
bLength 12
bDescriptorType 36
bDescriptorSubtype 3 (OUTPUT_TERMINAL)
bTerminalID 3
wTerminalType 0x0301 Speaker
bAssocTerminal 0
bSourceID 5
bCSourceID 7
bmControls 0x0003
Copy Protect Control (read/write)
iTerminal 11
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x81 EP 1 IN
bmAttributes 3
Transfer Type Interrupt
Synch Type None
Usage Type Data
wMaxPacketSize 0x0006 1x 6 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 14
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 1
bAlternateSetting 1
bNumEndpoints 2
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 15
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 1
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
iChannelNames 0
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 4
bBitResolution 32
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x02 EP 2 OUT
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0308 1x 776 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 0 Undefined
wLockDelay 0x0000
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x83 EP 3 IN
bmAttributes 17
Transfer Type Isochronous
Synch Type None
Usage Type Feedback
wMaxPacketSize 0x0004 1x 4 bytes
bInterval 4
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 0
bNumEndpoints 0
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 16
Interface Descriptor:
bLength 9
bDescriptorType 4
bInterfaceNumber 2
bAlternateSetting 1
bNumEndpoints 1
bInterfaceClass 1 Audio
bInterfaceSubClass 2 Streaming
bInterfaceProtocol 32
iInterface 17
AudioStreaming Interface Descriptor:
bLength 16
bDescriptorType 36
bDescriptorSubtype 1 (AS_GENERAL)
bTerminalLink 4
bmControls 0x00
bFormatType 1
bmFormats 0x00000001
PCM
bNrChannels 2
bmChannelConfig 0x00000003
Front Left (FL)
Front Right (FR)
iChannelNames 0
AudioStreaming Interface Descriptor:
bLength 6
bDescriptorType 36
bDescriptorSubtype 2 (FORMAT_TYPE)
bFormatType 1 (FORMAT_TYPE_I)
bSubslotSize 4
bBitResolution 32
Endpoint Descriptor:
bLength 7
bDescriptorType 5
bEndpointAddress 0x85 EP 5 IN
bmAttributes 5
Transfer Type Isochronous
Synch Type Asynchronous
Usage Type Data
wMaxPacketSize 0x0308 1x 776 bytes
bInterval 1
AudioStreaming Endpoint Descriptor:
bLength 8
bDescriptorType 37
bDescriptorSubtype 1 (EP_GENERAL)
bmAttributes 0x00
bmControls 0x00
bLockDelayUnits 0 Undefined
wLockDelay 0x0000The way the linux host driver views the device:
Code:
Linux 6.1.43-467115-gad02bcf12c1d-dirty with ff400000.usb Linux USB Audio Gadge
: USB Audio
Playback:
Status: Stop
Interface 1
Altset 1
Format: S32_LE
Channels: 2
Endpoint: 0x02 (2 OUT) (ASYNC)
Rates: 48000, 96000, 192000, 384000, 768000
Data packet interval: 125 us
Bits: 32
Channel map: FL FR
Sync Endpoint: 0x83 (3 IN)
Sync EP Interface: 1
Sync EP Altset: 1
Implicit Feedback Mode: No
Capture:
Status: Stop
Interface 2
Altset 1
Format: S32_LE
Channels: 2
Endpoint: 0x85 (5 IN) (ASYNC)
Rates: 48000, 96000, 192000, 384000, 768000
Data packet interval: 125 us
Bits: 32
Channel map: FL FRThanks for the feedback phofman. From readintg the above, I also note that the linux gadget seems seems to only propose 32 bits interface (and several sampling frequencies). This is interesting to me as it would allow to avoid to manage different alt settings for 12, 24 and 32 bits.
Do you confirm? Does it has some inconvenience in practice? Is it OK as Windows/Linux/Mac easily map 16 and 24 bits to 32 bits?
Nota: I also noted that that the OpenUAC bridge has only 2 configs (24 and 32 bits, no 16 bits).
Do you confirm? Does it has some inconvenience in practice? Is it OK as Windows/Linux/Mac easily map 16 and 24 bits to 32 bits?
Nota: I also noted that that the OpenUAC bridge has only 2 configs (24 and 32 bits, no 16 bits).
It's just that specific configuration of mine. Any number of bytes (integer format only, for now), any channels, any samplerate combination can be specified https://www.kernel.org/doc/Documentation/ABI/testing/configfs-usb-gadget-uac2 . It's just about copying byte arrays from/to the packet in the end
Multiple altsets with individual configurations are coming too https://lore.kernel.org/all/CAB0kiB.../T/#mc2b68c2e74ed57e2998c1b0f42bfca82e07db181
It has been a while since I worked on this but IIRC it is about Synopsys OTG used in STM32 MCUs. If FB packet frame number parity (odd or even) does not match to what host has sent Synopsys OTG sends an empty feedback packet. I did not spend much time on a workaround as easiest fix is to use bInterval = 1.
FB packets are sent but Win10 driver ignores them as they are empty.
This is how it looks like in Win10 uac2 driver logs:
This is how it looks like in Win10 uac2 driver logs:
Code:
[0]464C.4744::04/28/2024-17:05:08.806 [USBAudio2](0x01): FEEDBACK Isoch Buffers: BufferCount=3 BytesPerPacket=4 PacketsPerBuffer=16 PacketFreq=1000 PollingInterval=8
...
[0]464C.4744::04/28/2024-17:05:08.810 [USBAudio2](OUT): packetNumber=1 flags=0x00000000 eosPacketLength=21504
[0]0000.0000::04/28/2024-17:05:08.829 [USBAudio2](0x01): COMPL OUT buf 0 CurrenLinearPosition=1344
[0]0000.0000::04/28/2024-17:05:08.830 [USBAudio2](0x01): buf 0 feedback packet 0 has invalid packet length 0, ignoring packet
[0]0000.0000::04/28/2024-17:05:08.830 [USBAudio2](0x01): buf 0 feedback packet 1 has invalid packet length 0, ignoring packet
[0]0000.0000::04/28/2024-17:05:08.830 [USBAudio2](0x01): buf 0 feedback packet 2 has invalid packet length 0, ignoring packet
[0]0000.0000::04/28/2024-17:05:08.830 [USBAudio2](0x01): buf 0 feedback packet 3 has invalid packet length 0, ignoring packet
[0]0000.0000::04/28/2024-17:05:08.830 [USBAudio2](0x01): buf 0 feedback packet 4 has invalid packet length 0, ignoring packet