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> Usb Power Budget, Is powering usb peripherals unsafe?
post Nov 18 2006, 08:09 AM
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Joined: 19-October 05
From: Cardston, AB, Canada
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I'm running OZ on my C1000, but I think this is a fairly general question.

In kernel 2.16 and newer, if a USB device requires too much power, it is not enabled. 'dmesg' output might look like:

usb 1-2: no configuration chosen from 1 choice

To find out how much power a USB device wants, one can invoke:

lsusb -v | grep MaxPower

My card reader wants up to 250 mA, and my USB to serial converter says it might use up to 500 mA!

Post #3 on this ubuntu forum thread describes a work-around.

So my question is, is it safe to do this? [Also, I assume that people who are using kernels before 2.16 could well ask the same question, even if the device isn't automatically disabled.] Are the manufacturers of these USB products giving a high margin of error? Can a high-current device damage a Zaurus, or will it simply shorten battery life or just plain not work?

Thank you,

[Edit]. PS. Does it make any difference if the Z is plugged in or not?
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post Nov 18 2006, 07:36 PM
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From: Sydney, Australia
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there was a recent bug fix that turns off devices that will draw more power than is avalible. this affected many people as they had been running devices off unpowered ports without relising that the device wanted a powered one

there is somthing in the /sys tree to turn off this feature but i cant remeber where, it should be fine to turn off but its not recommended, if i remeber correctly the Z can do about 200mah and there is the chance that the power requirements were overstated or reflecta milisceond power spike to power up the device (in which case the capaitors will take care of the spike without loading the Z's power supply
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