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(bug?) jolla in charge mode fails to negotiate >500mA from USB pc controller [answered]

asked 2014-03-20 17:14:26 +0200

c.la gravatar image

updated 2014-08-27 11:14:48 +0200

jiit gravatar image

hi, I have Jolla USB setting set to charge only.

At home I use chargers plugged into 220V, outputting 5V and at least 1A.

At work I connect jolla to the pc, but I noticed it charges slower than at home. Using hunger Meter app as benchmark for a week I am pretty sure that at home Jolla charges at 1A while at work it charges at 500mA.

Jolla fails to talk to the USB host of the PC to ask for higher current (1A), a feature described in USB 2.0 specs. Even if in charge only Jolla should negotiate with the USB controller an higher current draw. Talking to USB controller is different than "talking" to the OS and transform the usb connection into a PC connection. The two things should be different.

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The question has been closed for the following reason "the question is answered, an answer was accepted" by c.la
close date 2014-03-21 15:23:52.580739

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answered 2014-03-20 17:33:13 +0200

Philippe De Swert gravatar image

updated 2014-03-20 17:39:02 +0200

This is not a bug. 500mA is the maximum current draw allowed for a USB port (in this case the Jolla is also a USB2.0 device so the new USB3.0 spec does not apply). 500mA and higher is only for dedicated charging ports which are not commonly implemented on PC's. Your PC at work has no charging port but a regular downstream USB one.

For a quick simplified overview look here: https://en.wikipedia.org/wiki/USB#Power

In short the Jolla does the right thing.

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I disagree. My old Nokia E52 can charge at 1A from usb ports.

I don't have time now to search for it, but usb 2.0 has an extension to the spec that allows the device to negotiate higher wattage with usb host controller if the controller supports it.

c.la ( 2014-03-20 18:44:59 +0200 )edit

"if the controller supports it." Exactly, this is the problem: If your USB host port does not allow for more (and most ports do not allow), you do not get more. On my notebook with 4 USB ports for example, there is a single port only allowing to draw a higher current.I.e. if you drew a higher current previously, make sure to use exactly the same port again.

jgr ( 2014-03-20 19:09:02 +0200 )edit

So, we don't really know if this is a bug or not, that would depend on what kind of port he has been trying. Can anyone confirm/reject this bug (using a USB-port that is known to permit 1A draw after negotiation)?

00prometheus ( 2014-03-20 19:24:55 +0200 )edit

Do you know any piece of software that tells you how much current is being drawn? I do not. And I am not going to cut a USB cable into pieces to run it through an amp meter.

jgr ( 2014-03-20 20:38:43 +0200 )edit

@c.la You can disagree all you want. The USB spec contradicts you. (page 171, 7.2.1 Classes of Devices in the usb 2.0 spec from usb.org) 500mA is the max for a downstream port, everything else is overcurrent. It is also very clear from the wikipedia link I showed you.

Btw in charging mode Jolla negotiates to get the higher 500mA, as standard we can only expect 100mA.

This is also why some hard disks etc come with the dual plug (which in itself is already a USB spec violation in a way). Because they can only expect 500mA from one port.

And I really doubt your E52 pulls 1A from your USB.

More links about this:

Or just google yourself for maximum USB port current

Yes higher currents are possible, but only for charging ports (which is like your dedicated charger)

Philippe De Swert ( 2014-03-20 21:56:38 +0200 )edit

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Asked: 2014-03-20 17:14:26 +0200

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Last updated: Mar 20 '14