Quoting Oktie Hassanzadeh <[EMAIL PROTECTED]>: > Is it possible to connect two computers with a simple cable or there > should necessarily be a special device for it? I know that there are some > cables with a special device that connect two computers in linux and their > driver is available in usbnet, but couldn't it be done by a simple cable? > Logically, There should be some way to do this, because USB is a port and we > should be able to access it's data lines directly,but why this is not done > before?
You need a special device (a "cable" with some electronics inside) because USB is -not- a port, it is a master-slave bus, and two masters (two PCs) can not talk to each other; they only can talk to slaves, and the "cable" device pretends to be a slave on both ends. Electrically, if you connect two USB ports of two computers: a) it will cause electrical overload in at least one computer, likely in both because two power supplies in two controllers are bound to be slightly different (+- 10% is allowed), and the difference voltage will be applied to a very low resistor (the cable), and the resulting current will shut down both power supplies, -hopefully-. Otherwise you will see some smoke ;-) [well, the current should be limited to 500 mA, but who knows if it really works as it is supposed to...] b) both USB host controllers (in both PCs) will report a failure and stop. This is because the "other" side will not be obeying the controller, and each HC will be hearing garbage on data lines. This will also result in bus contention (D+, D- lines), and if you are lucky the bus driver will just shut down; if you are not lucky, it will die, depending on how paranoid the HC designers were. Dmitri -- Eh, that's it, I guess. No 300 million dollar unveiling event for this kernel, I'm afraid, but you're still supposed to think of this as the "happening of the century" (at least until the next kernel comes along). (Linus, in the announcement for 1.3.27)
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