On Sun, 2 Jul 2006, Daniel Drake wrote: > Hi Alan, > > A Gentoo bug report has revealed the existence of devices with a > MaxPower value of greater than 500mA. If my understanding is correct, > these devices will always be rejected by the new configuration choosing > code. > > The bug report is here: > > http://bugs.gentoo.org/137208 > > How should we go about fixing it?
I see the problem. The Prolific device reports that it requires 510 mA. A strange number until you remember that the value stored in the descriptor is in 2 mA units. Which means the actual descriptor value is 255 -- apparently somebody thought they could just plug in the maximum 8-bit value and get away with it. How to go about fixing it? Well, nothing's wrong with the kernel so there's nothing to fix. Fixing the descriptors in the device would be a good thing, but obviously we can't do that. It might be worthwhile sending a bug report to Prolific, however. The only thing I can think of is to add a section on power budgeting to the FAQ at www.linux-usb.org, explaining what it is and how to bypass it manually. That way people could easily learn about the problems and what their options are. Do you feel up to writing a FAQ entry? Alan Stern P.S.: This business about drives requiring 1000 mA at startup... I don't know what the story is on that, but the USB spec does not permit a device to draw that much current. Possibly the USB-IDE converter unit includes sufficient capacitance that it can supply 1000 mA to the drive briefly while drawing only 500 mA from the bus. Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
