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There's no current specs for dual directional USB over any cable, afaik. There very well should be. You could present as a device and offer networking and have

There's no current specs for dual directional USB over any cable, afaik. There very well should be. You could present as a device and offer networking and have usb-ip advertised over multicast on that port. Easy, weekend project at most, would be dead obvious to any practitioner. USB4 as a packetized protocol really should offer something. I do wish there were like a half speed 2.5Gbit usb4 option, that microcontrollers could have some hope of accelerated bit banging.

FlyingAvatar 2y ago
Haven't USB hubs done this since USB 1.1?
- yonatan8070 2y ago
  I believe that the author is talking about plugging in a USB-C cable between your laptop and some headless system, and having your laptop send HID data, while also capturing a display output from the headless system
  - bonzini 2y ago
    Isn't that exactly what a USB-C docking station does? It receives display and audio data, and acts as a USB device (keyboard, mouse, webcam). You'd need hardware that can receive DisplayPort, but it's doable.
    - numpad0 2y ago
      Looks like an Alt Mode host with DP sink capability is technically allowed...? But it also looks like USB host controllers with Alt Mode support exposes internal DP source driver inputs, rather than handing you bunch of bare copper wires in Alt Mode, so I doubt it realistically has an implementation. ref: https://vesa.org/wp-content/uploads/2019/10/USB-DevDays-2019-VESA-DP-Alt-Mode-over-USB-Type-C.pdf https://vesa.org/wp-content/uploads/2019/10/USB-DevDays-2019...
BenjiWiebe 2y ago
Afaik this is 100% allowed by the spec. Flash drives are bidirectional (in and out). Hubs present multiple devices to the host through one cable. IDK why it isn't done more often in one device though.
- transpute 2y ago
  Looks like Belkin has a USB-C cable for VR headsets, which breaks out to DisplayPort (video) and USB-A (data) connectors, https://www.belkin.com/support-article/?articleNum=316883 https://www.belkin.com/support-article/?articleNum=316883
- numpad0 2y ago
  But neither USB nor DP(or DVI, VGA...) are symmetrical interfaces. They don't work like RS232C or Ethernet ports, a product that use these standards must be designed from beginning as a host or as a peripheral(or as a special 2-in-1 gadget that can exclusively switch roles). I think that's what GP meant by dual directional.
transpute 2y ago
According to Wikipedia, DisplayPort 2.0+ can coexist with USB data on the same cable, https://en.wikipedia.org/wiki/DisplayPort https://en.wikipedia.org/wiki/DisplayPort [2.0] .. using only two lanes on the USB-C connector via DP Alt Mode to allow for simultaneous SuperSpeed USB data and video [2.1] .. tightened its alignment with the USB Type-C specification as well as the USB4 PHY specification to facilitate a common PHY servicing both DisplayPort and USB4. In addition, DisplayPort 2.1 has added a new DisplayPort bandwidth management feature to enable DisplayPort tunnelling to coexist with other I/O data traffic more efficiently over the USB4 link.
- jauntywundrkind 2y ago
  I thought the comment was talking about both sides of the USB cable exposing devices to the other, when they said: > Is it theoretically possible to have 2-way HID

FlyingAvatar 2y ago

Haven't USB hubs done this since USB 1.1?

yonatan8070 2y ago
I believe that the author is talking about plugging in a USB-C cable between your laptop and some headless system, and having your laptop send HID data, while also capturing a display output from the headless system
- bonzini 2y ago
  Isn't that exactly what a USB-C docking station does? It receives display and audio data, and acts as a USB device (keyboard, mouse, webcam). You'd need hardware that can receive DisplayPort, but it's doable.
  - numpad0 2y ago
    Looks like an Alt Mode host with DP sink capability is technically allowed...? But it also looks like USB host controllers with Alt Mode support exposes internal DP source driver inputs, rather than handing you bunch of bare copper wires in Alt Mode, so I doubt it realistically has an implementation. ref: https://vesa.org/wp-content/uploads/2019/10/USB-DevDays-2019-VESA-DP-Alt-Mode-over-USB-Type-C.pdf https://vesa.org/wp-content/uploads/2019/10/USB-DevDays-2019...

BenjiWiebe 2y ago

Afaik this is 100% allowed by the spec. Flash drives are bidirectional (in and out). Hubs present multiple devices to the host through one cable. IDK why it isn't done more often in one device though.

transpute 2y ago
Looks like Belkin has a USB-C cable for VR headsets, which breaks out to DisplayPort (video) and USB-A (data) connectors, https://www.belkin.com/support-article/?articleNum=316883 https://www.belkin.com/support-article/?articleNum=316883
numpad0 2y ago
But neither USB nor DP(or DVI, VGA...) are symmetrical interfaces. They don't work like RS232C or Ethernet ports, a product that use these standards must be designed from beginning as a host or as a peripheral(or as a special 2-in-1 gadget that can exclusively switch roles). I think that's what GP meant by dual directional.

transpute 2y ago

According to Wikipedia, DisplayPort 2.0+ can coexist with USB data on the same cable, https://en.wikipedia.org/wiki/DisplayPort https://en.wikipedia.org/wiki/DisplayPort [2.0] .. using only two lanes on the USB-C connector via DP Alt Mode to allow for simultaneous SuperSpeed USB data and video [2.1] .. tightened its alignment with the USB Type-C specification as well as the USB4 PHY specification to facilitate a common PHY servicing both DisplayPort and USB4. In addition, DisplayPort 2.1 has added a new DisplayPort bandwidth management feature to enable DisplayPort tunnelling to coexist with other I/O data traffic more efficiently over the USB4 link.

jauntywundrkind 2y ago
I thought the comment was talking about both sides of the USB cable exposing devices to the other, when they said: > Is it theoretically possible to have 2-way HID