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?
The host and peripheral PHYs are different. Protocols going downstream and upstream are different. USB peripherals are literally not allowed to speak unless spoken to. It's always the king and his slaves. It's that way in the hardware.
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.
> 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.
Host-to-host connections over USB4 (which is Thunderbolt without Intel's marketing) actually just have a packet interface over which you can pass IP, no need for Ethernet emulation.
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?