On Mon, 16 Jan 2006, Z F wrote: > Hello everybody, > > I have a similar problem with an external drive. > The drive gets its main power via a power supply, but unfortunately > the usb controller on the external drive gets its power via USB. > I have a dual boot system and the drive works fine from windows, but > form linux, it does not get enough power (as it appears to me). > > Yes, there coould be a switch to tell the host USB controller to supply > more current (not voltage). I personally would think that such a switch > is stupid, unlees it is a powersaving mode. That is, if linux driver > sets the host controller output power to power save mode or something > like that. > It does not set the controller to the powersave mode, just the power > output > of the contoller. As I said, It makes no sence to me and I do not see > how this could be a linux problem, but it appears to me that it is. :-)
Warren, when the iPod or BlackBerry is plugged in for recharging, does a notification appear in the system log? Does the device get listed in /proc/bus/usb/devices? If not, that probably means the device is connected electrically but not logically -- it hasn't told the computer that it's attached to the USB port. (In technical terms, it hasn't turned on its D+ pullup resistor.) When no devices are attached to them, Linux does put USB controllers into a power-saving mode. Whether this means the amount of current delivered to the ports gets reduced is unclear (i.e., not documented). On the other hand, it _is_ clearly documented in the USB Specification that when a device hasn't told the computer it's attached, it's entitled to draw no more than 0.5 mA of current. If it does tell the computer it's attached, it may be allowed to draw as much as 500 mA. There's a bunch of "if"s here, and I can't tell what's really going on without more information. For instance, what shows up in the output from dmesg after the iPod or BlackBerry is plugged in? Do you have any other USB devices plugged in at the same time? For the disk drive these questions don't arise -- obviously the unit lets Linux know when it is plugged in. And maybe it does have problems... but how can you be sure those problems are at all related to the power supply? Alan Stern ------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Do you grep through log files for problems? Stop! Download the new AJAX search engine that makes searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
