5 ms·

I remember plugging in a damaged mouse into my old Win XP desktop and it displayed a nice notification saying "Your device tried to draw too much current and so

I remember plugging in a damaged mouse into my old Win XP desktop and it displayed a nice notification saying "Your device tried to draw too much current and so the USB port has been disabled." I fail to understand how such basic stuff has eluded USB C port manufacturers, specially on high end devices like Macbook and Pixel. >When you connect your USB-C-equipped Nexus 6P phone to a MacBook Air port designed to only provide 1.1A ... the phone can pull too much power ... and potentially destroy internal components. This is just nonsense, as far as I know. No device can "pull" more current than you can provide. Even if you short the pins, the port will just be shut down, as noted later in the article itself. >But Saunders, chairman of the USB-IF standards body, says he's not aware of any protection against a completely miswired cable like the one that struck down Leung's Chromebook Pixel. "That was something that the circuits of his notebook can't protect against," he says. I highly doubt that. What's the worst that can happen? You deliver 20V to the pin expecting GND. Trivial to protect against. And this is also only for things like chargers. If it is any peripheral device, the voltage drop will never exceed ~5V I'm guessing. All this just comes down to bad engineering on the part of laptop manufacturers. Bad cables, bad devices, reverse polarity chargers have always been present. And our computers have always had protections against them. And that is how it should be. A completely miswired cable should simply not work. Now if you're talking about differentials of >100V, then I would understand. But we're nowhere close to those levels. Google and Apple: Your ports are badly designed and you should feel bad!

zurn 11y ago
PC hardware often (including Macs) often have self-resetting fuses on USB ports that make the port look dead but come back to life after some time. Some fuses take longer than others. So it's sometimes easy to think your USB device killed the port. A friend had this with a Macbook and a USB charged bike torch. Apparently polyfuses can take days to properly un-trip.
- bravo22 11y ago
  Polyfuses are temperature driven and will reset within a few seconds. USB ports on non-cheap bare-minimum laptops use a chip in monitoring the current draw and can block that port. The OS can re-enable the port right away but I believe OS X requires you to reboot.
  - manarth 11y ago
    OS-X (Yosemite + El Capitan) has displayed the message to me: "Your device tried to draw too much current and so the USB port has been disabled". When I took the offending cable out, and tried with a different device, it worked straight away, no reboot required (not sure about earlier versions/alternative scenarios though, it's possible they do require a reboot).
  - zurn 11y ago
    I was going by a "polyswitch fundamentals" doc from a manufacturer[1] - and had the weasel-word "properly" :) Apparently the resistance falls quickly at first but can take a long time to fully return to pre-trip level. This has caused trouble in the Raspberry Pi. Users were getting odd effects when voltages didn't quite return to spec after polyfuse trip. [2] [1] http://www.te.com/content/dam/te-com/documents/circuit-protection/global/CPD-Catalog/S11_PolySwitch-Fundamentals.pdf http://www.te.com/content/dam/te-com/documents/circuit-prote... [2] http://elinux.org/Polyfuses_explained http://elinux.org/Polyfuses_explained
- thenomad 11y ago
  AHA! Interesting. This explains why my computer has a bunch of USB3 ports that work... sometimes. (It also very sporadically has a massive wibble and hard-crashes with an error relating to USB.)
deleted 11y ago
[deleted]
cnvogel 11y ago
> "Your device tried to draw too much current and so the USB port has been disabled." In USB 1 and 2 (probably also in 3, but I don't know about this), the device has two power modes. Initially it is only allowed to draw a few mA. This allows to power up enough of the device (the USB controller) so that the device descriptor can be read. The device descriptor tells the computer that the device requires some additional current. If in a chain of several non-externally powered hubs there's not enough capacity, the COMPUTER will NOT TELL THE DEVICE TO POWER UP. The computer can not turn off the voltage on the port. Typically USB interface chips will have an output pin that's only providing additional ("high power" circuitry) with power, by switching a mosfet, when the computer gave the OK to proceed. sudo lsusb -v (...) Device Descriptor: (...) Configuration Descriptor: bmAttributes 0xa0 (Bus Powered) Remote Wakeup MaxPower 500mA > I highly doubt that. What's the worst that can happen? You deliver 20V to the pin expecting GND. ...which means that you deliver -20V to the +5V rail.
- omgtehlion 11y ago
  > The computer can not turn off the voltage on the port Right here I have a roll (1000pcs) of chips that do exactly this (usb power management ICs) that cut power off and report this incident to controller. Maybe notebook manufacturers do not use them due to cost or space constarints...
  - cnvogel 11y ago
    Interesting. Could be that they are mandatory when you have ports sourcing higher currents? That would be reasonable, to avoid damage on shorts. -- But I've never seen such things on "simple" (500mA) ports, only polyfuses. I'd really be surprised if there would be anything but polyfuses on the "old WinXP PC" my original comments's parent comment referred to.
    - dfox 11y ago
      Common implementation of overcurrent protection on USB ports consists of polyfuse on VBUS and feedback pin from this fused VBUS to controller (to detect tripped polyfuse), on some devices such polyfuse is even shared by multiple ports. In theory, original USB1.1 expected the trip-point to be programmable, but most USB hosts are not implemented that way, because it requires some kind of low-drop high-side power switch that tends to be expensive.
russdill 11y ago
Having ground and vcc swapped is very different than just shorting ground and vcc. USB protects against overcurrent and transients, but if you are applying something above 5V or below 0V to any of the USB pins, all bets are off. Since the chromebook was ungrounded, 5V became ground. This means that from the laptops perspective, -5V was applied to the VCC pin. that's 10V out of spec.
- IshKebab 11y ago
  But that's not what happened here...
spacecowboy_lon 11y ago
Some one saved a few dollars in the price by not designing the ports to fail safe.
kbart 11y ago
I'm no expert in this area, but grounding should be much easier when PC is plugged in a socket as contrast to a battery powered device. Also, old PC's have had big, steel cases.

zurn 11y ago

PC hardware often (including Macs) often have self-resetting fuses on USB ports that make the port look dead but come back to life after some time. Some fuses take longer than others. So it's sometimes easy to think your USB device killed the port. A friend had this with a Macbook and a USB charged bike torch. Apparently polyfuses can take days to properly un-trip.

bravo22 11y ago
Polyfuses are temperature driven and will reset within a few seconds. USB ports on non-cheap bare-minimum laptops use a chip in monitoring the current draw and can block that port. The OS can re-enable the port right away but I believe OS X requires you to reboot.
- manarth 11y ago
  OS-X (Yosemite + El Capitan) has displayed the message to me: "Your device tried to draw too much current and so the USB port has been disabled". When I took the offending cable out, and tried with a different device, it worked straight away, no reboot required (not sure about earlier versions/alternative scenarios though, it's possible they do require a reboot).
- zurn 11y ago
  I was going by a "polyswitch fundamentals" doc from a manufacturer[1] - and had the weasel-word "properly" :) Apparently the resistance falls quickly at first but can take a long time to fully return to pre-trip level. This has caused trouble in the Raspberry Pi. Users were getting odd effects when voltages didn't quite return to spec after polyfuse trip. [2] [1] http://www.te.com/content/dam/te-com/documents/circuit-protection/global/CPD-Catalog/S11_PolySwitch-Fundamentals.pdf http://www.te.com/content/dam/te-com/documents/circuit-prote... [2] http://elinux.org/Polyfuses_explained http://elinux.org/Polyfuses_explained
thenomad 11y ago
AHA! Interesting. This explains why my computer has a bunch of USB3 ports that work... sometimes. (It also very sporadically has a massive wibble and hard-crashes with an error relating to USB.)

deleted 11y ago

[deleted]

cnvogel 11y ago

> "Your device tried to draw too much current and so the USB port has been disabled." In USB 1 and 2 (probably also in 3, but I don't know about this), the device has two power modes. Initially it is only allowed to draw a few mA. This allows to power up enough of the device (the USB controller) so that the device descriptor can be read. The device descriptor tells the computer that the device requires some additional current. If in a chain of several non-externally powered hubs there's not enough capacity, the COMPUTER will NOT TELL THE DEVICE TO POWER UP. The computer can not turn off the voltage on the port. Typically USB interface chips will have an output pin that's only providing additional ("high power" circuitry) with power, by switching a mosfet, when the computer gave the OK to proceed. sudo lsusb -v (...) Device Descriptor: (...) Configuration Descriptor: bmAttributes 0xa0 (Bus Powered) Remote Wakeup MaxPower 500mA > I highly doubt that. What's the worst that can happen? You deliver 20V to the pin expecting GND. ...which means that you deliver -20V to the +5V rail.

omgtehlion 11y ago
> The computer can not turn off the voltage on the port Right here I have a roll (1000pcs) of chips that do exactly this (usb power management ICs) that cut power off and report this incident to controller. Maybe notebook manufacturers do not use them due to cost or space constarints...
- cnvogel 11y ago
  Interesting. Could be that they are mandatory when you have ports sourcing higher currents? That would be reasonable, to avoid damage on shorts. -- But I've never seen such things on "simple" (500mA) ports, only polyfuses. I'd really be surprised if there would be anything but polyfuses on the "old WinXP PC" my original comments's parent comment referred to.
  - dfox 11y ago
    Common implementation of overcurrent protection on USB ports consists of polyfuse on VBUS and feedback pin from this fused VBUS to controller (to detect tripped polyfuse), on some devices such polyfuse is even shared by multiple ports. In theory, original USB1.1 expected the trip-point to be programmable, but most USB hosts are not implemented that way, because it requires some kind of low-drop high-side power switch that tends to be expensive.

russdill 11y ago

Having ground and vcc swapped is very different than just shorting ground and vcc. USB protects against overcurrent and transients, but if you are applying something above 5V or below 0V to any of the USB pins, all bets are off. Since the chromebook was ungrounded, 5V became ground. This means that from the laptops perspective, -5V was applied to the VCC pin. that's 10V out of spec.

IshKebab 11y ago
But that's not what happened here...

spacecowboy_lon 11y ago

Some one saved a few dollars in the price by not designing the ports to fail safe.

kbart 11y ago

I'm no expert in this area, but grounding should be much easier when PC is plugged in a socket as contrast to a battery powered device. Also, old PC's have had big, steel cases.