How to switch off power to USB ports when computer is switched off?

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Level 1

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How to switch off power to USB ports when computer is switched off?

Hi.

When I switch off my MacBook Pro but leave it connected to the AC adapter the USB ports remain powered. This can be seen by connecting an iPod to the MacBook Pro and then switch the MacBook Pro off. The iPod will continue charging.

Usually this is a nice feature. However I have an USB powered device (elgato eyeTv DVB-T stick), which blocks the entire USB bus when it stays powered on when the computer is powered off. When the computer is switched on again various USB devices are missing (internal Bluetooth, internal iSight and the eyeTv stick itself).

When the computer is powered by battery the USB power is automatically removed when the computer is switched off and everything works fine.

When the MacBook Pro runs Ubuntu Linux it also works fine, because Linux always switches off USB power on shutdown.

Is there a way to tell Mac OS X to always switch off USB power on shutdown? I have read the pmset and nvram manpages but not found what I am looking for.

An API would also be helpful, so I could write a little C program and run it everytime on shutdown. The last resort would be a custom kernel extension, but I hope to avoid that.

Thanks,
Jolanta Urban

MacBook Pro, Mac OS X (10.5.2)

Posted on Mar 20, 2008 7:51 AM

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Answer 1

parry_pb

Level 2

290 points

Mar 20, 2008 8:06 AM in response to jolantaurban

Have you checked libusb ( http://libusb.sourceforge.net/) ? Also check this - http://www.gniibe.org/ac-power-by-usb/ac-power-control.html where they have got a user space program to demonstrate the power control.

Hope this helps.

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Answer 2

jolantaurban Author

Level 1

0 points

Mar 20, 2008 12:25 PM in response to jolantaurban

I was able to work around this problem by connect the offending device to a "vivanco USB 2.0 HUB CLIP". This hub is powered by a seperate AC adapter.

However if the AC adapter of the USB hub is not plugged in the problem persists. It seems like Apple does something strange to the USB power supply when the notebook is switched off, but not disconnected form the power line. I have no multimeter here at the moment, but I guess that there is either undervoltage or the right voltage but the current is limited. This condition then crashes the controller of the eyeTv-Stick, which hangs the entire USB bus.

I hope that Apple will introduce a configurable option to switch off USB power. On my ThinkPad this can be configured in the BIOS setup.

Thanks for the helpful answer, I have not tried, because the USB hub was the cheaper and easier solution 😉

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Answer 3

May 1, 2008 5:36 PM in response to jolantaurban

While we're on the topic, here's a word of caution for using USB-powered fan cooling pads with the MBP:

Don't leave the fan plugged in when your laptop is off!

The fan will completely drain the battery. This has happened a couple of times to me, and I have noticed that my battery health suffers each time (as reported by iStatPro widget). Full battery drains such as that are bad for the battery.

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