Comment by rektide | Hacker News Reader

Comment by rektide | Hacker News Reader

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Tons of answers here. I think, if you want complex usb-pd offerings, you need to accept a pretty high $$$ price for all those power regulation subsystems you are demanding. I would be surprised to hear that indeed all the current offerings require wall power, that none can operate off laptop/uplink- I think you are wrong. But perhaps.

Overall I think the main current barrier to entry has been usb-c alt modes. If someone plugs a hdmi adapter into one of the hubs ports, ehat happens then? USB3+C's crazy lane splitting has been pretty suboptimal for figuring out what the role of a hub really is in the world today.

USB4 at least fixes that, makes usb a packet switched transport that tunnels other protocols. Now if someome plugs a displayport adapter into a hub, it's just going to use bandwidth. The whole tree under the usb-root doesnt have to totslly rebuild itself to make available a lane for some other purpose. The flexibility of usb-c, with it's two channels, is a complexity we've only finally specified a proper means to make use of. It's getting better. Looking forward to some other companies starting to offer hub chips, seeing this young new scene begin to evolve.

My understanding is that Displayport is already packetized, having USB4 packetize it again seems suboptimal? I think both Displayport and HDMI have official specs that work over the USB-C connector.

It's adding a small percent overhead in exchange for making it routable over a hub. Without the extra header it requires dedicated lanes.

USB-C has two physical channels, and the act of having to decide that a channel needs to be used for usb or hdmi or displayport is a complication that hubs were never well specified to handle. Hence there not being many such hubs.

USB4's tunneling means that the connector does not have to enter an alt-mode. Even when transmitting displayport or hdmi, the hub or hubs and host can remain using usb4. As well as making hubs suddenly make sense (after being an unspecified ball of confusion with alt modes), this allows bandwidth sharing that was previously impossible.

In short, that these other specs had packets is irrelevant, because those solutions werent really compatible with hub-like devices. There needed to be a common mode of interoperation, which hadnt existed before usb4.

>I think both Displayport and HDMI have official specs that work over the USB-C connector.

You've answered your own question here. "over the USB-C connector" meaning direct connections between two devices. The moment you put a hub inbetween it won't work.

USB C Port -HUB-> DP Port works, USB C Port -HUB-> 4x USB C port -USB-C-to-Display-Port-adapter-> DP Port does not.

> I would be surprised to hear that indeed all the current offerings require wall power, that none can operate off laptop/uplink- I think you are wrong. But perhaps.

Indeed, there are products that don't require wall power. I got a Chinese model [0] off Amazon that does Ethernet + 4K@60 over DP/HDMI (alt-mode, not DisplayLink) and can even drive an external spinning drive, all from the USB connection from the PC. The catch is that it comes with a dual-port cable, meaning it requires two (adjacent!) ports to work. I haven't tried it with a regular cable, so I don't know whether that's a hard requirement. It's also able to do PD pass-through if you connect it to a wall.

One downside is that I've sometimes had the screen go dark for a second, and other people have complained about this on the Amazon page. So it's not clear how reliable this will be in the long run.

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[0] https://www.amazon.fr/gp/product/B09MTTZ36K

Does USB4 tunnel original USB (1.0-2.0), or is that still on its own separate pins? I was under the impression that electrical and timing requirements meant it was virtually impossible to tunnel it while remaining in spec.

Worse: at least thunderbolt provided USB downstream ports by including a PCIe-backed USB root controller. On USB4, all USB 2.0 downstream devices have to share the limited USB 2.0 bandwidth at the upstream port. They could have just specified a translator like they did for USB 1.1 -> USB 2.0, but they didn't and it's not possible to make one that works reliably/portably.

> makes usb a packet switched transport

Guess that means the next logical step is to evolve USB into ethernet.

You kid, but USB PD reinvented ethernet among other things: https://nitter.net/whitequark/status/1035760558237204480?lan...

Eventually ethernet always wins.

and then infiniband.

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