RE: [usb] Why is the PC always the host???

["kw@nie" <kwanie@pacific.net.sg>]

Hi Olivier,

PCs are always host because they have only host controller in them. Unless
they are specifically design to have dual functionality, host controller can
only function as host. By dual functionality, I mean a chip with both host
and device controller on it. Unfortunately, this is not the case for the
chips used in PCs. The very reason why most PC OSes, if not all, have no
generic device support.

There are some newer embedded microprocessors that have both host and device
controllers on-chip. These uP are intended for handheld computing
applications, e.g. PDAs and webpads. When connected to a PC the PDA is a
device, e.g. synchronization of a PDA. But when you attach a USB device to
the PDA then it will function as host, e.g. a USB keyboard.

Cheers,
kwanie

 -----Original Message-----
From: 	owner-usb@opencores.org [mailto:owner-usb@opencores.org]  On Behalf
Of omaud@etud.insa-tlse.fr
Sent:	05 March 2002 21:33
To:	usb@opencores.org
Subject:	[usb] Why is the PC always the host???


I already asked a question last week and I need to know something else:

It may be a stupid question: I am wondering why the PC is always the host in
USB. Is it due to the host-controller (is it
possible
to define host-controller as a device?) or is it due to the OS (windows). In
other words, is it possible to modify the
host-controller in order to see the PC as a device?

Thanks for any informations,
Olivier MAUD
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