Still some questions about USB

Question

Hi, few days ago I asked here about implementing USB. Now, If I may, would like to ask few more questions, about thing I dind´t quite understood.

So, first, If I am right, Windows has device driver for USB interface, for the physical device that sends and receives communication. But what this driver offers to system (user)? I mean, USB protocol is made so its devices are adressed. So you first adress device than send message to it.

But how sophisticted is the device controller (HW) and its driver? Is it so sophisticated that it is a chip you just send device adress and data, and it writes the outcomming data out and incomming data to some internal register to be read, or thru DMA directly to memory?

Or, how its drivers (SW) really work? Does its driver has some advanced functions like send _data to _device? Becouse I somewhat internally hope there is a way to directly send some data thru USB, maybe by calling USB drivers itself? Is there any good article, tutorial you know about to really explain how all this logic works? Thanks.

Answer 1

The USB protocol stack has several layers and is quite complex. You really need to read a good book on USB (e.g. USB Complete) to get an understanding of how it all fits together. The bottom line though is that you want to go as high up the protocol stack as you can, ideally using a system level API (e.g. if it's a USB HID device then just treat it like any other HID device, rather than thinking if it as a USB device - ditto for mass storage devices, etc).