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Comment by bradrn | Hacker News Reader

Later in the conversation someone links to a Twitter exchange which I found quite interesting:

> (@m_ou_se) I just tried to charge my phone by connecting it to my laptop (with USB-C), but instead of my phone, my laptop started getting charged, quickly draining my phone's battery. Uh, what.

> (@Gankra_) in case you aren't familiar: there was a semantic function of asymmetric usb cables that symmetric usb-C has broken. to "fix" this, each device picks a number for how subby it is, and the less subby one is the dom and charges the sub. these numbers can be surprising.

> (@m_ou_se) After some experimenting, I concluded that Dell laptops are the most powerful USB-C PD doms followed by ThinkPads, while phones and MacBooks are (equally) subby. Connecting phones and MacBooks with each other results in a switch fight.

(https://twitter.com/m_ou_se/status/1502664680602492933)

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But wasn't there supposed to be a way to change the roles afterwards, according to user input?

It would be super useful at times to charge one laptop (or phone) off the other - provided I have some way to specify which one should be charged.

The most appropriate and most sexual way would be to have a safe word.

At this point, it might make more sense to just put a condom over all male USB connectors.

Still wondering if technically the host would be the dom since it gets all the control or if the device would be the dom since it gets all the power.

I have USB c to c cable that will charge in one direction. It’s not labeled, so I put some arrows on it :)

This thread is getting more and more interesting.

The fact that this is such a rare comment is damning.

I thought whichever one is plugged in second is the one that receives the charge, but it may be vice versa. Either way, it's the order of plugging that matters.

Does a device even know that it's connected to a ded cable? I'd imagine that it's only after you plug in the second device that they both suddenly see they're being connected to something.

I believe that some cables (especially conversion cables) can have some sort of processor. I have no idea if that's the case with USB-C cables, though.

How can devices determine if a cable is plugged in without a device on the other end? Difference in resistance?

I'm not sure how it works in reality but in principle the cable could act like a jumper across two contacts on the computer's USB connector.

The connectors have chips in them which communicate with the device they're plugged in to. E.g.: https://www.cabledo.com/anker-usb-c-to-usb-c-2-0-100w-cable-...

Not all cables have chips in them, only things like high-power (5A) cables need a chip. A basic 3A USB-C cable will not have any chip.

Is there really nothing standard about USB-C?

They’ve done a stellar job of standardising the name. So many different cables & capabilities, one standardised name.

If you wait long enough they'll try to rename WiFi as USB-C somehow

Does USB-C suffer from the problems with interference that USB 3 did?

Perhaps that could be harnessed into something more productive.

If there are two ground pins in the connector and the cable shorts those two ground pins, the connector could use the presence of continuity between those two ground pins to know a cable is plugged in but not connected to another device. Something like that.

> But wasn't there supposed to be a way to change the roles afterwards, according to user input?

At least on Android, there is; it's in the same place where you choose which file sharing protocol should be used (it's in the Android notifications area, it says something like "Charging the device through USB; click here for more options").

In practice this hasn't worked for me. I got a new phone and was trying to charge it on the way home (since it was activated automatically by the store despite me not asking for that). It refused to charge in the direction I wanted. It'd reset this option instantly every time

This metaphor seems backwards. Wouldn't the sub give its power to the dom?

Never heard of a power bottom?

Typically no, unless it’s a power bottom.

https://m.youtube.com/watch?v=Uc9_mxvP1K0

Now dymk, I heard speed has something to do with it.

Speed has everything to do with it (although the cable must be rated for fast charging)

How one interprets this question is like a personality test

Is there like a C function, dll or device manager property I can check to find out how subby or dom my device is or is this only possible via comparison?

This is more interesting than the linked poll, thanks.

My M1 Max MacBook Pro treats my Galaxy Tab A8 like an external battery which makes development quite annoying. It's strange that this hasn't been figured out in 10 years.

On Android you can configure that (usually there's a popup after plugging in, if not it should be in the power settings) on multiple levels - if it should charge, if OTG charging (the phone/tablet providing power) is enabled, etc.

If you've set this and it doesn't work properly still, try swapping out the cable. A bad quality USBC cable would always make my phone (occasionally) charge my MacBook but not the other way around, for some unknown reason. Drove me crazy until I changed the cable.

I can't fathom how we all went ten years without knowing this stuff.

Didn't have a laptop with USB-C ports until 2021. I've got a couple now.

One does PD, one does not. One does video out, one does not. One charges fast, and you guessed it, one does not.

Is it supposed to be easy because the cables fit? Honestly, it's only made it harder and I know what I'm doing. "It fits but doesn't do what I was told it would" is probably more confusing to the average Joe.

But but everything used usb-c so iPhones must be usb-c now toooooo!!!

I like the physical connection of usb-c but that’s it. The whole thing is an absolute mess.

I’m going to miss lightening port.

> everything used usb-c so iPhones must be usb-c now toooooo

EU agrees with this.

No you're not. Even the worst USB-C cable is better than lightning. An iPhone doesn't charge another device. So you're good.

Also, then hopefully I won't need to switch out cables every so often because of a shorting pin #4.

If you plug in a semi recent Samsung phone to a USB-c monitor, not only will it charge, but you will also get some kind of desktop experience on the monitor.

> phones and MacBooks are (equally) subby.

Do you mean phones here or iPhones? I've been charging my LG phones (G6 & G8) from MacBook Pros for years and never noticed an unexpected switch.

As you're touching on, it doesn't make sense to make a blanket statement for all phones. Also, iPhone is not USB-C, so I guess it doesn't participate in this negotiation.

What about Lightning to USB-C cables? I assume the device is talking the USB protocol at that point? Or does that connection only allow charging in one direction?

I've charged my iPhone off my MBP using a lightning->usb-c cable and I didn't notice anything weird. I've also been able to charge my iPhone off my iPad using the same cable so maybe it is one way.

That particular cable only works in one direction. Lightning itself can power external devices, but the whole mechanism is completely different than how USB PD over USB-C works (it is designed for low power peripherals and thus can output unregulated 3-ish V in order to save on DC/DC conversion losses, similar capability of devices powered entirely from V_CONN is quite recent and hackish addition to USB-C).

I forget that other interface still exists. Is it only iPhone and keyboard/touchpad/mouse/pencil now?

AirPods too.

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