What "environment" are you in, Leekyungyeol? In Linux, we could "sys_open", "sys_read", "sys_write"... same as to any other file... as far as I know. I ASSume it's similar for Windows(?). If you need to do this without support from some OS - from a bootsector, say... I've been told that you do *not* want to attempt to write a "usb stack"(
) in asm. (not saying I believe it, but that's what I've been told)
I don't have much experience with usb. I plugged a camera into a usb port once - "sys_open"ed it and the LED came on (much farther than I ever got with a camera plugged into the parallel port!!!). I "sys_read" from it and got some data. Never got as far as converting it into an image... got distracted...
One of my housemates has gone out of town, and left behind (among other things) a couple of "pen drives". I might "borrow" one to experiment with. Is that the type of usb device you're interested in? (I guess the "u" in "usb" is for "universal", so I guess we might be dealing with a lot of different devices... consistant interface? We'll find out, I guess...)
What have you tried that you found "difficult"? How "raw" do you need it?
Best,
Frank