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Is it theoretically possible to have 2-way HID (keyboard, mouse) and 1-way video output on a single USB-c cable? It would simplify connection to a KVM or softwa

Is it theoretically possible to have 2-way HID (keyboard, mouse) and 1-way video output on a single USB-c cable? It would simplify connection to a KVM or software-emulated display/keyboard/mouse. Low FPS would be enough for dashboards and CLI.

jauntywundrkind 2y ago
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
deleted 2y ago
[deleted]
tomcam 2y ago
Can someone explain the downvotes?
yonatan8070 2y ago
I don't think you can do it direcly. I recently found the Openterface Mini-KVM [1], which is supposed to allow you plug it into your laptop over USB-C, and some arbitrary system with USB+HDMI. Then, using their host software, view the HDMI display output and send mouse and keyboard inputs with ease. I haven't tried it, so I can't speak to how well it works, but it sounds promising. It is a crowdfunded project, so the usual caveats apply [1] https://openterface.com/ https://openterface.com/
- transpute 2y ago
  This thread has gone from: could exist? not possible specs imply yes? exists as open hw/sw Thanks so much for the pointer! https://www.crowdsupply.com/techxartisan/openterface-mini-kvm https://www.crowdsupply.com/techxartisan/openterface-mini-kv... > KVM-over-USB .. macOS, Windows, and Linux [clients], with Android support in development.. HDMI and emulated keyboard/mouse (HID) input.. video up to 1920x1080@30Hz with under 140ms latency.. play target device's audio directly on the host computer.. [send text] from the host to the target device, ideal for copying usernames, passwords.. Switchable USB-A Port.. for transferring files.. or sharing other USB devices. With USB storage emulation, this approaches BMC remote mgmt, minus network attack surface.
  - numpad0 2y ago
    I think most people just weren't sure what you're talking about. Communications between such a thingamajig capture card and a laptop has nothing to do with DP Alt mode or USB HID, it's whatever custom USB packet types that capture card manufacturer comes up with. That technically wouldn't be an answer to your original comment in strict sense. The most likely heuristic paraphrasing for your original query is something like "are there ways to multiplex DP _source_ and HID _peripheral_ on a single USB3+DP Alt connection". That made no sense at multiple levels on top of being unlikely to be possible. That lead to people hallucinating wildly. The alternate question "are there ways to plug an SBC into laptop somehow for remote control, over a single USB-C cable" has that dongle as an answer as we now know in hindsight. But that is not a straightforward interpretation and response for your original comment, especially with your follow-up replies about DP Alt mode specs that would not be used by such a device.
rcarmo 2y ago
You can get the RP2XX0 PIO to control an extra USB host port. I've been keeping tabs on RP2040 resources: https://taoofmac.com/space/hw/rp2040 https://taoofmac.com/space/hw/rp2040
u8080 2y ago
Yes, this theoretically could be done using DP Alt-mode for type-c. It allows up to 4 lanes(commonly 2 lanes) DP signal over typically USB3 assigned lanes. USB2 data lanes are still functional in this mode. https://newnex.com/technology-articles-dp-alt-mode-over-usb-c.php https://newnex.com/technology-articles-dp-alt-mode-over-usb-...
g15jv2dp 2y ago
This already exists, right now...? I've seen tons of USB hubs with an hdmi output and several USB ports that can be used concurrently. Hell I'm using one right now. Are you asking about something else?
- transpute 2y ago
  This is for connecting an SBC to a laptop via one USB-c cable. The laptop emulates a display and sends kb/mouse events to the SBC. Another comment pointed out a $100 board that can tunnel USB data + video on one cable.
silon42 2y ago
You can easily have PD+DP+USB (but limited to 2.0).

jauntywundrkind 2y ago

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

deleted 2y ago

[deleted]

tomcam 2y ago

Can someone explain the downvotes?

yonatan8070 2y ago

I don't think you can do it direcly. I recently found the Openterface Mini-KVM [1], which is supposed to allow you plug it into your laptop over USB-C, and some arbitrary system with USB+HDMI. Then, using their host software, view the HDMI display output and send mouse and keyboard inputs with ease. I haven't tried it, so I can't speak to how well it works, but it sounds promising. It is a crowdfunded project, so the usual caveats apply [1] https://openterface.com/ https://openterface.com/

transpute 2y ago
This thread has gone from: could exist? not possible specs imply yes? exists as open hw/sw Thanks so much for the pointer! https://www.crowdsupply.com/techxartisan/openterface-mini-kvm https://www.crowdsupply.com/techxartisan/openterface-mini-kv... > KVM-over-USB .. macOS, Windows, and Linux [clients], with Android support in development.. HDMI and emulated keyboard/mouse (HID) input.. video up to 1920x1080@30Hz with under 140ms latency.. play target device's audio directly on the host computer.. [send text] from the host to the target device, ideal for copying usernames, passwords.. Switchable USB-A Port.. for transferring files.. or sharing other USB devices. With USB storage emulation, this approaches BMC remote mgmt, minus network attack surface.
- numpad0 2y ago
  I think most people just weren't sure what you're talking about. Communications between such a thingamajig capture card and a laptop has nothing to do with DP Alt mode or USB HID, it's whatever custom USB packet types that capture card manufacturer comes up with. That technically wouldn't be an answer to your original comment in strict sense. The most likely heuristic paraphrasing for your original query is something like "are there ways to multiplex DP _source_ and HID _peripheral_ on a single USB3+DP Alt connection". That made no sense at multiple levels on top of being unlikely to be possible. That lead to people hallucinating wildly. The alternate question "are there ways to plug an SBC into laptop somehow for remote control, over a single USB-C cable" has that dongle as an answer as we now know in hindsight. But that is not a straightforward interpretation and response for your original comment, especially with your follow-up replies about DP Alt mode specs that would not be used by such a device.

rcarmo 2y ago

You can get the RP2XX0 PIO to control an extra USB host port. I've been keeping tabs on RP2040 resources: https://taoofmac.com/space/hw/rp2040 https://taoofmac.com/space/hw/rp2040

u8080 2y ago

Yes, this theoretically could be done using DP Alt-mode for type-c. It allows up to 4 lanes(commonly 2 lanes) DP signal over typically USB3 assigned lanes. USB2 data lanes are still functional in this mode. https://newnex.com/technology-articles-dp-alt-mode-over-usb-c.php https://newnex.com/technology-articles-dp-alt-mode-over-usb-...

g15jv2dp 2y ago

This already exists, right now...? I've seen tons of USB hubs with an hdmi output and several USB ports that can be used concurrently. Hell I'm using one right now. Are you asking about something else?

transpute 2y ago
This is for connecting an SBC to a laptop via one USB-c cable. The laptop emulates a display and sends kb/mouse events to the SBC. Another comment pointed out a $100 board that can tunnel USB data + video on one cable.

silon42 2y ago

You can easily have PD+DP+USB (but limited to 2.0).