Nintendo Switch + LG UltraFine 4K

[funn3r]

Yes it its 2019 4K LG UltraFine with 2 TB3 and 3 USB-C.

Model number on the box is 24md4kl-b

[Mira Yurizaki]

Even if the USB-C supports DP Alt mode, the monitor won't work if you feed it a raw DP signal. The basis of this statement comes from reading http://www.ti.com/lit/wp/slly021/slly021.pdf

 

This part in particular is what does it (emphasis added):

Quote

The Type-C Alt Mode Specification, allows for protocols other than USB to be transferred over a USB connection, such as DisplayPort, HDMI, MHL or Thunderbolt over the Type-C interface. Alternate Mode can be enabled only via a USB PD protocol handshake through structured vendor-defined messages (VDM) to discover, configure, and to enter or exit Alt Modes.

 

Or more accurately, the Configuration Channel pin on USB-C is responsible for figuring out what kind of device is talking to the USB Host. From https://www.silabs.com/community/mcu/8-bit/knowledge-base.entry.html/2016/09/26/what_s_the_role_ofc-kQYe

 

Quote

For the USB Type-C solution, two pins on the connector, CC1 and CC2, are used to establish and manage the Source-to-Sink connection.

Functionally, the configuration channel is used to serve the following purposes.
• Detect attach of USB ports, e.g. a Source to a Sink
• Resolve cable orientation and twist connections to establish USB data bus routing
• Establish data roles between two attached ports
• Discover and configure VBUS: USB Type-C Current modes or USB Power Delivery
• Configure VCONN
• Discover and configure optional Alternate and Accessory modes

To me this makes sense. The USB host can't simply infer what's connected to it if it doesn't even know how to talk to the device. This is similar to why phone modems talk at the base rate of 300bps: they know this is guaranteed and they figure out during the beeps and boops what speed they can really talk at.

 

In any case, converting the Switch from USB-C DP -> HDMI -> DP isn't going to work because at this point, any ability to connect to a USB-C host was lost in the conversion to HDMI. The DP signal isn't going to know how to talk to the USB-C port, and I wouldn't expect it to because there are no pins from the DP connector that would be sufficient. And even if there were any pins, DP doesn't know how to talk to USB (which I'm guessing there's a USB specific protocol that's used over the CC pins to standardize the process)

[Kilrah]

Yup. It would need an active, unidirectional HDMI/DP to USB-C DP that includes a controller to handle that aspect, which as mentioned doesn't exist.

[funn3r]

And what about this ? https://www.belkin.com/us/p/p-f4u098/

I guess both HDMI are outpus

[Kilrah]

Yes.

[brentcas]

I went through this same rabbit hole and found this conversation to be helpful. I have the latest LG UltraFine 5K and am looking to connect my Xbox to it. I've been looking into the capture card route, but would like to preserve 4K 60 HDR quality. Currently, the Elgato HD60S+ looks like it will only send a 1080p 60 fps video to the Mac app. From what I've read, the 4K HDR 60 fps signal is only going to the TV that it's passing through to. Any ideas on whether there's another capture card that would allow 4K60 HDR "capture" to the Mac?