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Re: usb-sticks not recognized

At 4:31 PM +0100 11/10/05, Joerg Mertins wrote:

Some pruduce an error message saying that the USB-port provides too little power, with some of them my powerbook is not even recognizing that anything at all got plugged into the usb-port, even when used direkly at the computers plug with no other usb-devices connected. 

What do you mean by a "usb stick"?

There are 2 very similar alerts which can arise like this. One is that the device declares more power in its descriptors than the port can supply. The other is that the device has drawn excessive power so the port has gone into an over current condition and been shut down.

If the device declares more power than is available, it will not work in that port, it needs to be moved to a high powered port. If you get this from a high powered port, such as when its directly connected to the computer, that woudl indicate a problem with the device's descriptors. (Such as declaring an illegal amount of power in the configuration descriptor.) Checking them with USB Prober would be a good idea.

The other alert should never arise, it is a pathalogical condition for a grossly misbehaving device. You can check how much power the device draws with a multimeter or oscilloscope and a current probe. The scope method will show you more information about transient overcurrent conditions. A USB device should never (ever) draw more than 500mA from a USB port. PowerBooks current limiting is more sensitive than other computers as power is a big constraint in a portable system. It is possible that an out of spec device will not trip the overcurrent on some computers, but will on others, its still the device which is out of spec.

So I'd check the power declared in the descriptors, and check the device's actual current use.

Also for any example of a device not being recognised, I'd reboot the machine first. An over-current can shut down the port until boot, a stuck driver can prevent any further devices from being recognised at a port.
--
Barry Twycross
email@hidden
---
USB, it's not a Dyslexic BUS. (Thanks to TC.)
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