Windows X Unix in USB communication

Question

inHi, this question is fast, but from my point of view its pretty hard. I have been messing with implementing USB device built from MCU. So I found project called V-USB which is software-emulated USB interface for Atmel MCUs. But this is not so important.

The question is, on their site, they say that using custom USB class, you can simply write host software on Unix, but you need driver DLL for Windows. The problem is, they dont explain why.

So, please, why? I dont know Unix based systems, but I thought that the very basics of different OS are the same becouse thay rise from the same hardware, and even Unix cannot do HW IO operations from user mode.

I know about libraries for USB communication like LibUSB and so, but I want to know the very reason why thay say that its easy on Unix. Thanks.

EDIT: Thanks for answer, but can I have further question? How this everything is a file works? I mean, my vision of driver on Windows is a program running in kernel mode, thus allowed to access CPU IO ports, which either provides functions to OS by some standarts, to allow Windows to use it (for example HDD driver must be accessible from filesystem driver by standardised set of functions, to allow any HDD work the same).

With this all you have to do is call drivers via WinAPI function or directly call its functions. But USB implements new feature which is different classes. So there is main USB root driver to handle USB and calling right secondary drivers for right devices. Than there is the same procedure, you just call your USB driver.

But if in Unix everything is a file, how are handled different classes? I just cannot imahine how this works in some analogy to Windows way. Does that file represents the way to communicate with USB root driver?

Answer 1

Everything in UNIX is a file, which supports simple operations. No matter if you are communicating via a terminal or a via a usb device, everything is a stream of bytes to a file.

* read
* write
* lseek
* close