Table of contents :
- Tab presentation
- USB frame capture workflow
- Selected options storage map
- Frame details
- Implementation guide
This tab offers options to route the mixer audio to USB output. It also allows to set the USB output level, in dB.
Each USB output has the corresponding audio routing options :
And the USB output level has the following options :
We can now suppose that there is a way to transmit these options settings from the computer to the device, in order to tell the device from which source to route audio to the USB output.
For each USB output, I placed the audio routing option on None, and I captured
the USB traffic when changing the option from None to another one from the
list. I then repeated this capture for each options of the list, and finally,
to capture the change for the None option, I initially set the option to
CHX Timecode CD/LINE.
For the USB output level options, I used the same principle : one capture per option change.
All the captures are available in the captures directory. They are
still noisy due to the polling behavior of the Setting Utility in order to
determine the position of the input switches for the
Mixer input tab.
However, by looking at one of the captures,
I saw that there were URB_CONTROL out request and response.
To ease the reading of the capture files, you can use this wireshark filter :
usb.transfer_type == URB_CONTROL && usb.endpoint_address.direction == OUT
By comparing the payload of the request in each capture files, I was able to determine how the Setting Utility was sending the options informations to the device.
The information for the USB output audio routing is stored in the wValue field
of the URB request payload, with a fixed value for the wIndex field :
wValue: 0x0100
wIndex: 32770 (0x8002)
The wValue value is stored on two bytes (0xAABB) where the first byte (AA)
is the USB output number, and the second byte (BB) is the routing option
value.
By looking at the USB output audio routing captures, we can see that the selected options are transmitted as following :
| USB output number | wValue first byte value (AA) |
|---|---|
1/2 |
01 |
3/4 |
02 |
5/6 |
03 |
7/8 |
04 |
| Audio routing source | wValue second byte value (BB) |
|---|---|
CHX Timecode PHONO |
03 |
CHX Timecode CD/LINE |
00 |
CHX Timecode LINE |
01 |
Post CHX Fader |
06 |
Cross Fader A |
07 |
Cross Fader B |
08 |
MIC |
09 |
REC OUT |
0a |
None |
0f |
So, for instance, wValue: 0x0100 means that the USB 1/2 output has the
CHX Timecode CD/LINE audio source.
The information for the USB output level is also stored in the wValue field of
the URB request payload, with another fixed value for the wIndex field :
wValue: 0x0300
wIndex: 32771 (0x8003)
This time, only the first byte of the wValue field is used to store the
selected option, the second byte is always set to 00 : 0xAA00.
By looking at the USB output level captures, we can see that the selected option is transmitted as following :
| USB output level | wValue first byte value (AA) |
|---|---|
-5dB |
03 |
-10dB |
02 |
-15dB |
01 |
-19dB |
00 |
So, for instance, wValue: 0x0300 means that the USB output level is set to
-5dB.
The USB output audio routing frames are from the
captures/usb12/none_to_timecode_cdline.pcapng
file.
The USB output level frames are from the
captures/usb_output_level/-19dB_to_-5dB.pcapng
file.
USB frame sent by the Setting Utility to the device to set the USB 1/2 output
audio source to CHX Timecode CD/Line :
Frame 145: 64 bytes on wire (512 bits), 64 bytes captured (512 bits) on interface usbmon1, id 0
Interface id: 0 (usbmon1)
Interface name: usbmon1
Encapsulation type: USB packets with Linux header and padding (115)
Arrival Time: Feb 17, 2021 18:57:46.584375000 CET
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1613584666.584375000 seconds
[Time delta from previous captured frame: 0.007645000 seconds]
[Time delta from previous displayed frame: 0.000000000 seconds]
[Time since reference or first frame: 1.031065000 seconds]
Frame Number: 145
Frame Length: 64 bytes (512 bits)
Capture Length: 64 bytes (512 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: usb]
USB URB
[Source: host]
[Destination: 1.12.0]
URB id: 0xffff8e6b45d66900
URB type: URB_SUBMIT ('S')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
Device: 12
URB bus id: 1
Device setup request: relevant (0)
Data: present (0)
URB sec: 1613584666
URB usec: 584375
URB status: Operation now in progress (-EINPROGRESS) (-115)
URB length [bytes]: 0
Data length [bytes]: 0
[Response in: 146]
Interval: 0
Start frame: 0
Copy of Transfer Flags: 0x00000000
.... .... .... .... .... .... .... ...0 = Short not OK: False
.... .... .... .... .... .... .... ..0. = ISO ASAP: False
.... .... .... .... .... .... .... .0.. = No transfer DMA map: False
.... .... .... .... .... .... ..0. .... = No FSBR: False
.... .... .... .... .... .... .0.. .... = Zero Packet: False
.... .... .... .... .... .... 0... .... = No Interrupt: False
.... .... .... .... .... ...0 .... .... = Free Buffer: False
.... .... .... .... .... ..0. .... .... = Dir IN: False
.... .... .... ...0 .... .... .... .... = DMA Map Single: False
.... .... .... ..0. .... .... .... .... = DMA Map Page: False
.... .... .... .0.. .... .... .... .... = DMA Map SG: False
.... .... .... 0... .... .... .... .... = Map Local: False
.... .... ...0 .... .... .... .... .... = Setup Map Single: False
.... .... ..0. .... .... .... .... .... = Setup Map Local: False
.... .... .0.. .... .... .... .... .... = DMA S-G Combined: False
.... .... 0... .... .... .... .... .... = Aligned Temp Buffer: False
Number of ISO descriptors: 0
[bInterfaceClass: Unknown (0xffff)]
Setup Data
bmRequestType: 0x40
0... .... = Direction: Host-to-device
.10. .... = Type: Vendor (0x2)
...0 0000 = Recipient: Device (0x00)
bRequest: 3
wValue: 0x0100
wIndex: 32770 (0x8002)
wLength: 0
USB frame sent by the device to the Utility Setting to aknowledge the USB output audio routing setting :
Frame 146: 64 bytes on wire (512 bits), 64 bytes captured (512 bits) on interface usbmon1, id 0
Interface id: 0 (usbmon1)
Interface name: usbmon1
Encapsulation type: USB packets with Linux header and padding (115)
Arrival Time: Feb 17, 2021 18:57:46.584451000 CET
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1613584666.584451000 seconds
[Time delta from previous captured frame: 0.000076000 seconds]
[Time delta from previous displayed frame: 0.000076000 seconds]
[Time since reference or first frame: 1.031141000 seconds]
Frame Number: 146
Frame Length: 64 bytes (512 bits)
Capture Length: 64 bytes (512 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: usb]
USB URB
[Source: 1.12.0]
[Destination: host]
URB id: 0xffff8e6b45d66900
URB type: URB_COMPLETE ('C')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
Device: 12
URB bus id: 1
Device setup request: not relevant ('-')
Data: not present ('>')
URB sec: 1613584666
URB usec: 584451
URB status: Success (0)
URB length [bytes]: 0
Data length [bytes]: 0
[Request in: 145]
[Time from request: 0.000076000 seconds]
Unused Setup Header
Interval: 0
Start frame: 0
Copy of Transfer Flags: 0x00000000
.... .... .... .... .... .... .... ...0 = Short not OK: False
.... .... .... .... .... .... .... ..0. = ISO ASAP: False
.... .... .... .... .... .... .... .0.. = No transfer DMA map: False
.... .... .... .... .... .... ..0. .... = No FSBR: False
.... .... .... .... .... .... .0.. .... = Zero Packet: False
.... .... .... .... .... .... 0... .... = No Interrupt: False
.... .... .... .... .... ...0 .... .... = Free Buffer: False
.... .... .... .... .... ..0. .... .... = Dir IN: False
.... .... .... ...0 .... .... .... .... = DMA Map Single: False
.... .... .... ..0. .... .... .... .... = DMA Map Page: False
.... .... .... .0.. .... .... .... .... = DMA Map SG: False
.... .... .... 0... .... .... .... .... = Map Local: False
.... .... ...0 .... .... .... .... .... = Setup Map Single: False
.... .... ..0. .... .... .... .... .... = Setup Map Local: False
.... .... .0.. .... .... .... .... .... = DMA S-G Combined: False
.... .... 0... .... .... .... .... .... = Aligned Temp Buffer: False
Number of ISO descriptors: 0
[bInterfaceClass: Unknown (0xffff)]
USB frame sent by the Setting Utility to the device to set the USB output level
to -5dB :
Frame 409: 64 bytes on wire (512 bits), 64 bytes captured (512 bits) on interface usbmon1, id 0
Interface id: 0 (usbmon1)
Interface name: usbmon1
Encapsulation type: USB packets with Linux header and padding (115)
Arrival Time: Feb 17, 2021 19:21:51.626988000 CET
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1613586111.626988000 seconds
[Time delta from previous captured frame: 0.015503000 seconds]
[Time delta from previous displayed frame: 0.347120000 seconds]
[Time since reference or first frame: 3.067756000 seconds]
Frame Number: 409
Frame Length: 64 bytes (512 bits)
Capture Length: 64 bytes (512 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: usb]
USB URB
[Source: host]
[Destination: 1.12.0]
URB id: 0xffff8e6baf2a3600
URB type: URB_SUBMIT ('S')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
Device: 12
URB bus id: 1
Device setup request: relevant (0)
Data: present (0)
URB sec: 1613586111
URB usec: 626988
URB status: Operation now in progress (-EINPROGRESS) (-115)
URB length [bytes]: 0
Data length [bytes]: 0
[Response in: 410]
Interval: 0
Start frame: 0
Copy of Transfer Flags: 0x00000000
.... .... .... .... .... .... .... ...0 = Short not OK: False
.... .... .... .... .... .... .... ..0. = ISO ASAP: False
.... .... .... .... .... .... .... .0.. = No transfer DMA map: False
.... .... .... .... .... .... ..0. .... = No FSBR: False
.... .... .... .... .... .... .0.. .... = Zero Packet: False
.... .... .... .... .... .... 0... .... = No Interrupt: False
.... .... .... .... .... ...0 .... .... = Free Buffer: False
.... .... .... .... .... ..0. .... .... = Dir IN: False
.... .... .... ...0 .... .... .... .... = DMA Map Single: False
.... .... .... ..0. .... .... .... .... = DMA Map Page: False
.... .... .... .0.. .... .... .... .... = DMA Map SG: False
.... .... .... 0... .... .... .... .... = Map Local: False
.... .... ...0 .... .... .... .... .... = Setup Map Single: False
.... .... ..0. .... .... .... .... .... = Setup Map Local: False
.... .... .0.. .... .... .... .... .... = DMA S-G Combined: False
.... .... 0... .... .... .... .... .... = Aligned Temp Buffer: False
Number of ISO descriptors: 0
[bInterfaceClass: Unknown (0xffff)]
Setup Data
bmRequestType: 0x40
0... .... = Direction: Host-to-device
.10. .... = Type: Vendor (0x2)
...0 0000 = Recipient: Device (0x00)
bRequest: 3
wValue: 0x0300
wIndex: 32771 (0x8003)
wLength: 0
USB frame sent by the device to the Utility Setting to aknowledge the USB output level setting :
Frame 410: 64 bytes on wire (512 bits), 64 bytes captured (512 bits) on interface usbmon1, id 0
Interface id: 0 (usbmon1)
Interface name: usbmon1
Encapsulation type: USB packets with Linux header and padding (115)
Arrival Time: Feb 17, 2021 19:21:51.627124000 CET
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1613586111.627124000 seconds
[Time delta from previous captured frame: 0.000136000 seconds]
[Time delta from previous displayed frame: 0.000136000 seconds]
[Time since reference or first frame: 3.067892000 seconds]
Frame Number: 410
Frame Length: 64 bytes (512 bits)
Capture Length: 64 bytes (512 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: usb]
USB URB
[Source: 1.12.0]
[Destination: host]
URB id: 0xffff8e6baf2a3600
URB type: URB_COMPLETE ('C')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
Device: 12
URB bus id: 1
Device setup request: not relevant ('-')
Data: not present ('>')
URB sec: 1613586111
URB usec: 627124
URB status: Success (0)
URB length [bytes]: 0
Data length [bytes]: 0
[Request in: 409]
[Time from request: 0.000136000 seconds]
Unused Setup Header
Interval: 0
Start frame: 0
Copy of Transfer Flags: 0x00000000
.... .... .... .... .... .... .... ...0 = Short not OK: False
.... .... .... .... .... .... .... ..0. = ISO ASAP: False
.... .... .... .... .... .... .... .0.. = No transfer DMA map: False
.... .... .... .... .... .... ..0. .... = No FSBR: False
.... .... .... .... .... .... .0.. .... = Zero Packet: False
.... .... .... .... .... .... 0... .... = No Interrupt: False
.... .... .... .... .... ...0 .... .... = Free Buffer: False
.... .... .... .... .... ..0. .... .... = Dir IN: False
.... .... .... ...0 .... .... .... .... = DMA Map Single: False
.... .... .... ..0. .... .... .... .... = DMA Map Page: False
.... .... .... .0.. .... .... .... .... = DMA Map SG: False
.... .... .... 0... .... .... .... .... = Map Local: False
.... .... ...0 .... .... .... .... .... = Setup Map Single: False
.... .... ..0. .... .... .... .... .... = Setup Map Local: False
.... .... .0.. .... .... .... .... .... = DMA S-G Combined: False
.... .... 0... .... .... .... .... .... = Aligned Temp Buffer: False
Number of ISO descriptors: 0
[bInterfaceClass: Unknown (0xffff)]
From the above frame details and response data analysis, we can issue some
details in order to implement the features of the Mixer output tab.
In order to set the USB output audio routing, we have to send a URB request to the device having the following attributes :
USB URB
URB type: URB_SUBMIT ('S')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
URB length [bytes]: 0
Data length [bytes]: 0
Setup Data
bmRequestType: 0x40
0... .... = Direction: Host-to-device
.10. .... = Type: Vendor (0x2)
...0 0000 = Recipient: Device (0x00)
bRequest: 3
wValue: 0x0100
wIndex: 32770 (0x8002)
wLength: 0
Refer to the USB output audio routing map
in order to determine the value of the wValue attribute.
Also consider that not all USB outputs have the same option choices (c.f. the
screenshots in the tab presentation).
In order to set the USB output level, we have to send a URB request to the device having the following attributes :
USB URB
URB type: URB_SUBMIT ('S')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
URB length [bytes]: 0
Data length [bytes]: 0
Setup Data
bmRequestType: 0x40
0... .... = Direction: Host-to-device
.10. .... = Type: Vendor (0x2)
...0 0000 = Recipient: Device (0x00)
bRequest: 3
wValue: 0x0300
wIndex: 32771 (0x8003)
wLength: 0
Refer to the USB output level map
in order to determine the value of the wValue attribute.
The response from the device should contain the following attributes :
USB URB
URB type: URB_COMPLETE ('C')
URB transfer type: URB_CONTROL (0x02)
Endpoint: 0x00, Direction: OUT
0... .... = Direction: OUT (0)
.... 0000 = Endpoint number: 0
URB status: Success (0)
URB length [bytes]: 0
Data length [bytes]: 0