>Well so why simply not modify the actual USB source code to make it do similar >tasks as the ones performed >with USB OTG so that we can have computers switching from host to slave? (said >like this it sounds very >simple but I'm sure that it'd take me ages to get to that result if that could >ever be done).
Well, to begin with USB OTG is for point-to-point. It will not allow multiple devices on the bus using USB hubs. Secondly, USB OTG requires diferent hardware than normal USB comms. >I mean what makes it impossible in the implementation to make a usb port of a >computer acts like a device, > what should be changed? Hardware should be changed. USB OTG is not a software extension of existing ptotocol, it is effectively difefrent standard alltogether. If both ends support it, they can negotiate to switch to this mode. It was designed for slave to behaev as a master. What you want is master behaving as a slave. You really should read some books on USB then you will see the difference. As an example, think of connecting two PC's using RS-232. You need null modem cable, right? There is nothing you can do in software to make one PC a DCE. It is always DTE. Rudolf ----- Original Message ----- From: "Rudolf Ladyzhenskii" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Subject: FW: [linux-usb-devel] dummy USB port Date: Fri, 12 Nov 2004 10:29:21 +1100 > > > USB is master-slave arrangement. > > Master is completely different from slave! Different hardware and software. > > As for USB OTG, I beleive this is to allow USB slaves to talk to each other > without the host controller. This is need, for example, to print from digital > camera to printer without need of host PC. > In the USB OTG arrangement two slaves negotiate who is taking responsibility > of the bus master. It is a separate standard from normal USB. > > Rudolf > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Alan > Stern > Sent: Friday, November 12, 2004 10:17 AM > To: omar kfitz > Cc: [EMAIL PROTECTED] > Subject: Re: [linux-usb-devel] dummy USB port > > > On Thu, 11 Nov 2004, omar kfitz wrote: > > > > > Hi everyone, > > I actually want to know why we need special USB cables for Host to Host > > transfer files using USB (I actually own one those special cables)? . > > What aspects of that protocole restrict its use to a host to device > > (master -slave) and restain transfer file from a computer to another > > using a simple cable A to A? > > The design of USB is such that all transfers are initiated by the host. > Also it's not set up to handle the collisions that would occur if more > than one device tried to transmit at the same time. And there's the fact > that slave devices attached to a USB bus must be configured by a host > before they can function. These and many other similar considerations > mean that USB won't work unless the bus has exactly one host. > > > > I'm a newbie in USB technologie, and to > > tell the truth I've been through the USB specfication not without > > problems. Actually I thought that maybe we could access the usb source > > systemfiles under Linux and modify them to get a dummy USB root acting > > as a slave and not a master so that we could get a master slave system > > with two computers. I'm almost sure it s impossible, but I need to know > > why in that case. Has anyone ever tried this and can tell me why it > > wouldn't work? > > Most host controllers are not designed to operate as slaves, and it's > impossible to make them do so. As just one example, a slave is not > supposed to supply power to the Vbus line but a master is. > > No one has ever tried it because there's no way to do it. > > On the other hand, there is the USB OTG ("On The Go") specification, which > provides a way for a device to act as either a host or a slave. Two OTG > devices can be connected to each other using a symmetrical cable and they > will be able to communicate (and transfer files, for example). Almost no > Linux computers have OTG hardware, however, and standard hardware does not > support OTG. > > Alan Stern > > > > ------------------------------------------------------- > This SF.Net email is sponsored by: > Sybase ASE Linux Express Edition - download now for FREE > LinuxWorld Reader's Choice Award Winner for best database on Linux. > http://ads.osdn.com/?ad_id=5588&alloc_id=12065&op=click > _______________________________________________ > [EMAIL PROTECTED] > To unsubscribe, use the last form field at: > https://lists.sourceforge.net/lists/listinfo/linux-usb-devel > > > ------------------------------------------------------- > This SF.Net email is sponsored by: > Sybase ASE Linux Express Edition - download now for FREE > LinuxWorld Reader's Choice Award Winner for best database on Linux. > http://ads.osdn.com/?ad_idU88&alloc_id065&op=click > _______________________________________________ > [EMAIL PROTECTED] > To unsubscribe, use the last form field at: > https://lists.sourceforge.net/lists/listinfo/linux-usb-devel > > So-deska!!! -- _______________________________________________ Find what you are looking for with the Lycos Yellow Pages http://r.lycos.com/r/yp_emailfooter/http://yellowpages.lycos.com/default.asp?SRC=lycos10 ------------------------------------------------------- This SF.Net email is sponsored by: Sybase ASE Linux Express Edition - download now for FREE LinuxWorld Reader's Choice Award Winner for best database on Linux. http://ads.osdn.com/?ad_idU88&alloc_id065&op=click _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
