I have just moved into a new postion where I need to work with USB hubs. We have a portable device (I.e battery, limited power) with USB On The Go and need to drive a USB thumb drive. The thumb drive takes more current than we have but a powered USB hub should work. (Note the word should, I don't know the facts.) I need to understand all the communications that goes on between host and hub and device. Part of it is that the device says how much current it needs and the host must evaluate that and decide if the host can provide the current. But a powered hub throws more options into the game. I don't know what they are. The documents I find are not detailed in this area.
This is probably too much information for a specific answer in a forum. I am hoping for some pointers as to where I can find the information.
That's all handled by the USB controller in hardware and its firmware.
Contact Intel if you want to know more, they're a major manufacturing of the required chips.
There is also this book. USB Complete . it isn't a perfect book but easier than reading the approximately 1000 pages that make us the USB specification.
