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USB On-The-Go

(computer.rip)
208 points jnord | 2 comments | 03 Jan 25 12:42 UTC | HN request time: 0.449s | source
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crote ◴[04 Jan 25 05:55 UTC] No.42592767[source]▶
> Application notes from several USB controller vendors explain that, oddly enough, the only way to perform role reversal with USB-C is to implement USB Power Delivery (PD) and use the PD negotiation protocol to change the source of power. In other words, while OTG allows reversing host and device roles independently of the bus power source, USB-C does not. The end supplying power is always the host end.

This isn't true. USB PD has both "data role swap" and "power role swap" commands, and they are independent from each other.

It even allows for things like a "fast role swap", where you can unplug the power source from a dock (so power now has to flow from laptop to dock, instead of dock to laptop) without any interruption of the data connection.

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1. dec0dedab0de ◴[07 Jan 25 15:29 UTC] No.42623373[source]▶
It sounds like you’re talking about protocol, and the article is talking about implementations.
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2. danhor ◴[07 Jan 25 16:48 UTC] No.42624462[source]▶
Every USB-C docking station that exposes USB ports while also supplying the attached computer with power uses this feature, letting the computer act as a host and the docking station as the power source