![]() ![]() =>Device Descriptor This is an Interface Class Defined Device =>Endpoint Descriptor Direction: OUT - EndpointID: 2 =>Endpoint Descriptor Direction: IN - EndpointID: 1 =>Device Information Device Bus Speed: High Now we have two proper self-powered 3.5inch Seagate external and both work fine. So I take out my non-working USB-IDE case which uses 2 USB cable. per USB socket") it seems like Maxim actually if not openly encourages than at least subtly nudging a developer to brake the standard. Reading the article (" all host USB host devices like PCs and notebooks can source at least 500mA. Also, the enumeration is almost instantaneous, makes a difference if you are testing 500 devices! This makes Mac a very nice platform to develop on. on the keyboard) are limited to their respective (low/high) current budgets. Main host ports and low power hub ports (e.g. Macs DO detect overcurrent individually per each port and DO shut down offending port leaving the rest unaffected. Maybe Maxim should cast their nets wider than the PCs from their nearest shop. They may not be "compliant," but they do function. This is born out by the appearance in the market of USB powered reading lights, coffee mug warmers, and other similar items that have no communication capability. So no matter what dialog takes place (or does not take place) between a USB peripheral and host, 5V (at either 500mA or 100mA, or even maybe 2A or more) will be available. Notebook and motherboard makers are barely willing to pay for fault protection, let alone smart power switching. There may an exception to this statement, but I have yet to see it. ![]() In actual practice, no USB host shuts off USB power for anything other that an electrical fault (like a short). USB Ports rarely (never) turn off power: The USB spec is not specific about this, but it is sometimes believed that USB power may be disconnected as a result of failed enumeration, or other software or firmware problems. ![]() Furthermore, while some PCs use 10-20% accurate IC-based protection, other will use much less accurate poly-fuses (fuses that reset themselves) that will not trip until the load is 100% or more above the rating. So a four-port system may supply over 2A from one port if the other ports are not loaded. The protection device is set above the TOTAL power rating of all the ports. In fact, output current from a port often exceeds several Amps since multi-port systems (like PCs) frequently have only one protection device for all ports in the system. In any case, a USB port can never be counted on to limit its output current to 500mA, or any amount near that. Though the upper limit specifies that the current never exceed 5A, but a wise designer should not rely on that. Though the USB spec provides details about how much current a USB port must supply, there are mile-wide limits on how much it might supply. Some observed USB characteristics that may not be obvious, yet can influence power designs, are: Though USB is, with little doubt, one of the best thought out, reliable, and useful standards efforts in quite some time, it has not been immune to the impact of the real world. With any standard, it's interesting to see how actual practice diverges from the printed spec or how undefined parts of the spec take shape. That is kind of strange. It is a bit hard for me to believe this is real. Are you suggesting that host OS will allow them to get enough power and do not shut down them once they specify the wrong things (specify self-power and 0mA but actually bus-powered)?. I suspect that this may be because it draws too much power, but I haven't done any debugging to verify it yet. Some unexpected disconnects on a desktop PC with multiple other bus powered USB devices, though. The device seems to sort-of-work on all computers I've tried so far. I find it really hard to believe that this shows something else than the USB device is sending. IdVendor 0x1058 Western Digital Technologies, Inc.ĭevice Qualifier (for other device speed): Mine looks like this:īus 004 Device 005: ID 1058:0702 Western Digital Technologies, Inc.īDeviceClass 0 (Defined at Interface level) Note that the link shows someone else's drive. I don't have access to any Windows PC at the moment. It is unlikely lsusb will give wrong result but I feel it strange if Western Digital could be wrong on this. Just in case, you may want to check with USBview or similar tools under Windows. What is the software you used to get the descriptor? Seems to be lsusb under Linux. WD even sells a USB power booster cable just in "those rare cases, this cable can be used to power the drive using power from two USB ports on the system". ![]()
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