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fedora-users: Re: Charging USB devices with Fedora

Re: Charging USB devices with Fedora

From: Tim <ignored_mailbox_at_nospam>
Date: Wed Mar 17 2010 - 11:52:03 GMT
To: kari.somby@gmail.com, Community support for Fedora users <users@lists.fedoraproject.org>

On Wed, 2010-03-17 at 12:49 +0200, Kari Somby wrote:
> The protocol says that max current for one USB host is 500 mA.

Which is not available to plugged in devices by default. The power
supply feature is initially only a low current, and can be increased
when the device negotiates with the host.

The initial "low current" supply was originally 100mA, but later this
was changed to 150mA. But, because the original was lower, you can only
reasonably expect to get 100mA out of a port, by default.

The maximum current available was 500mA (after negotiation), later this
was increased. But, again, because the original was lower, you can only
reasonably expect to get 500mA from one host.

It's expected that the device plugged into the port would be the thing
to do the negotiation. Though it could be possible for software on the
computer to program the power power. That would be what those special
charging programs do.

Just like there are devices which ignore the specs, and try to get power
that they don't deserve, there will be hosts that ignore the specs, and
can always supply more power than the specifications.

I still think it's rather dumb to use an expensive computer to replace a
cheap charger or power supply.

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