5 ms·
What do you mean by "first device plugged in"? If I connect two devices with an USB-C cable, which one is the "first device" then?
by ohuf 5y ago
What do you mean by "first device plugged in"? If I connect two devices with an USB-C cable, which one is the "first device" then?
- andrei_says_ 5y agoI imagine you’d plug the cable into one of them and then the other. I assume the author means first and second as in temporal order.
- technobabbler 5y agoA device can tell when one end of the cable is plugged in by testing the cable's control channel, even without the other end connected yet. It sees that a cable is connected, but there's nothing on the other end, and presumes it's first and should act as the provider. A second later, you connect the other end of the cable to a consumer, and the first device will try to negotiate its role with the second. It's up to the devices to respect each other's role requests. http://blog.teledynelecroy.com/2016/02/usb-type-c-cable-detection.html http://blog.teledynelecroy.com/2016/02/usb-type-c-cable-dete... Different device types (like a powered hub or desktop monitor) can request different roles, and they'll have to sort it out during negotiation if there's a conflict. Sometimes a user-facing popup will ask you if you want to provide or take power from the other device.