In all seriousness though, the current state of a USB is ridiculous.
My wife innocently asked me why her USB C phone isn't triggering Android Auto in the car, and straight away you know it's because she bought a USB C power-only cable without knowing the difference.
Nice.
They're pretty nice too, the only made in Germany USB-C/lightning cables I have ever used.
Maybe it's possible to make one lacking both USB 2 and 3 data though, but I haven't seen one yet.
Nor have I seen a public USB-C outlet, for that matter, and I probably wouldn't be plugging my laptop or phone into one anyway: My own charger doesn't only protect me against bad intent, but also against cheap charging circuits that might or might not accidentally expose 220 Volt to my laptop's mainboard in case of faults.
Ouch. USB-C is even more fucked up than I thought… How does that even works with USB wall chargers?
> Nor have I seen a public USB-C outlet, for that matter
There are plenty of USB-A outlet everywhere (airport, trains, hotels, etc.), and most recent Android phones have only an USB-C port…
If they want to supply more than 5V/3A, they need to support the power delivery protocol too.
> There are plenty of USB-A outlet everywhere (airport, trains, hotels, etc.), and most recent Android phones have only an USB-C port…
Exactly: These are USB-A outlets. These are possible to implement using only a resistor network to announce the maximum charging current and always supply 5V, which is much easier to implement than variable voltage and the power delivery protocol. USB-C can do this too, but only up to 5V/3A.
USB-C devices are usually backwards compatible with all three of these when using an A-to-C cable or adapter: Legacy USB-A current identification via the D+/D- pins, USB-C resistor-based current identification via the configuration pins of USB-C and USB power delivery.
Less generally, these batteries can also break ground loops, which comes in handy when connecting a power supply to both a USB device and an attached analog audio device (e.g., iPhone and wired noise-canceling earbuds).
You'll note that many chargers started dropping handshaking because it was inconvenient. To be compatible with anything you need it, but there's many that don't ask, though they may only work with the equipment they were sold with. (E.g. defaults to 5V 2A charging.)
The historical design intent of USB is that, even when your laptop is in standby it still powers devices like your keyboard (so you can press keys to wake it up) and in exchange, devices promise to consume less than 2.5 milliamps (12.5 milliwatts) until they've negotiated permission to draw more from the host. After all, it'd suck if your laptop battery was going down noticeably even when the laptop was in standby.
Of course, loads of vendors of cheap devices ignore this - the makers of a $5 rechargeable bike light or USB fan aren't going to put in the components needed to negotiate charging speed. But in principle if you made a USB cable with only the power pins connected, compliant devices should only charge exceptionally slowly, if at all.
(Wall chargers, instead of enumerating as a USB host to negotiate power, used to put a certain value of resistor across the data lines, to signal what current the device could draw - this hasn't always been standardised, which is why phones and USB chargers can be incompatible)
Note also a fair number of laptops (read: every one I have used and checked) use PS/2 internally because it is interrupt driven and even lower power than USB. There are also plenty of laptops that advertise high current phone charging while off, some of which do negotiation, some of which don't.
[0] http://msdn.microsoft.com/en-us/library/windows/hardware/hh8...
Ignoring that, I'm not sure it's an improvement. Most of the power savings is having the keyboard initiate an interruptible event to wake the computer. Interpreting HID like in USB means the keyboard can't wake the computer, the computer needs to remain on to service USB interrupt endpoints.
The laptop I had with an always-on charging port actually charged things faster in standby, because that turned off the negotiation.
> defaults to 5V 2A charging
i don't think you understand how power transfer works.
voltage is applied (by the charger), and current is drawn (by the device that wants to charge). a charger cannot "dump power into" anything.
when chargers and devices attached to them engage in some sort of negotiation, that's not the device telling the charger what to do, that's the charger telling the device what its limitations are.
if you attempt to draw 3A from a device that can only do 2A, the voltage will drop outside of the specified range. to the extent that a charger can limit the charging current, it does so by dropping/cutting off the voltage until the current goes down. which isn't ideal for devices.
(perhaps you're confused by thinking that USB "chargers" are like battery chargers, and arbitrary USB devices somehow act like batteries. that's all wildly wrong.)
The main concern behind negotiation seems to be safety of the user and safety of the power supply. Detecting a safe load means detecting a not-short.
The basis for the 5V power negotiation on USB is extremely silly. The power supply is already current limited, protecting you from shorts, and the supply voltage is ~5V, quite far from anything dangerous.
This may be true for wall chargers but not devices capable of supplying power to peripherals while on battery power themselves.
For example, an external hard drive should not have to figure out that a large tablet can power it, while a phone won't, though trial and error, by attempting to spin up the disks multiple times.
Devices are going to misbehave anyway, it's probably more important to default to a reasonable level of mostly works.
Android already allows you to only use an USB connection for charging. Setting this as the default when you are in an unknown place sounds reasonable.
OTOH, a USB Y-cable physically has no data lines connected on the extra USB-A male connector; it thus provides a far stronger guarantee that there is no data travelling across them. (Not foolproof, but safer than a software-controlled switch.)
If you don't trust that cellphone won't transfer your private data via USB, I don't understand why you trust it not to do it via any wireless connection.