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.
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
could exist?
not possible
specs imply yes?
exists as open hw/sw
> 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.
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.
As mentioned by others, there are USB-C docking stations/monitors where a single cable provides power to the device, takes video from the device, and sends keyboard/mouse events to the device. I should have asked whether software on a laptop could emulate a USB-C docking station, i.e. DP display sink + keyboard + mouse, since docking stations already exist.
> 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.
Revisiting the question above, could a manufacturer make capture card output compatible with existing USB-C docking stations, instead of inventing bespoke USB packet types? If custom hardware is needed, why not emulate standard protocols?
I was surprised to learn that Windows/Linux/Mac/Android userspace software can encode/decode custom USB packets from a USB-C cable, without a custom kernel driver. Could RP2350 implement a similar custom protocol at the other end of the cable, removing the need for a hardware capture device?
You can make such a standalone computer, painted in orange and marketed as an ice cream, that works as the king class when a slave-class is connected to its sole USB-C port, and as a slave class when a king-class like a laptop connected to it. This is in fact how many smartphones work. But that's again not what you asked.
Exactly what you're asking in the way you're asking, standard USB protocols(and DisplayPort signals) going in and out of devices and computers freely like Ethernet packets, just isn't possible with USB.
That reminds me of Intel Thunderbolt Share [1][2], which offers sharing of screen/keyboard/mouse between 2 PCs, and is probably software-emulated ethernet over Thunderbolt.
[1] https://download.intel.com/newsroom/2024/client-computing/th...
[2] https://www.pcworld.com/article/2330173/meet-thunderbolt-sha...
Linux driver is here https://github.com/torvalds/linux/blob/master/drivers/net/th...
Another comment pointed out a $100 board that can tunnel USB data + video on one cable.
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.
[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.
> Is it theoretically possible to have 2-way HID
ref: https://vesa.org/wp-content/uploads/2019/10/USB-DevDays-2019...
IDK why it isn't done more often in one device though.