On Sat, May 30, 2015 at 10:20:18PM +0200, Maciej Żenczykowski wrote: > Communication over a true serial port can be implemented with a couple > dozen assembly instruction (ie. a few dozen bytes of machine code). > > USB is ridiculously complex and thus requires a few thousand if not > tens of thousands of lines of higher level code. > > Basically USB is not just a special serial connection, but also huge > amounts of power negotiation, auto-negotiation, packet framing, etc.
But at a hardware level it is still 4 wires. Ground, RX, TX, (and vcc which need not be dealt with). I am not talking about those thousands of lines of code or even interfaceing with it. I am talking about throwing those thousands of lines of code away, and using the hardware as a simple serial line. Code for serial lines is very old and well tested. This should not be difficult. Look at how one uses USB on Linux, when one uses a usb port to connect a router. One uses screen, or minicom, which is serial port software, to talk to hardware, which is ordinary used as a usb port. It seems to me it should be trivial to do the same thing on the other end of the line. Can my question be reconsidered from this point of view? > > Yes, it is theoretically doable, but it's unlikely anyone would ever > want to, especially since network tftp based recovery is for the most > part already implemented and much nicer to use. > > On Sat, May 30, 2015 at 12:42 PM, Paul Elliott > <[email protected]> wrote: > > > > > > I have noted that there are some routers that have in addition > > to the usual internal uart that can be connected with a > > TTL converter, they also have an external usb connection. > > > > A usb connection is just a special serial connection at > > a special voltage. > > > > Why could not the failsafe mode of these routers use the > > externally connected usb port for its serial console. > > > > Then it would be possible to unbrick these routers, when the > > net connnection does not work, without ever opening the router > > to connect to the uart. Instead a data cable between the > > external usb connection and the fixing computer could be used. > > > > What would be required to implement this idea? Could it be done > > with a tailored version of openwrt? Or would in be needed to > > hack u-boot? > > > > Thank You for thinking about this question. > > > > > > > > > > -- > > Paul Elliott 1(512)837-1096 > > [email protected] PMB 181, 11900 Metric Blvd Suite > > J > > http://www.free.blackpatchpanel.com/pme/ Austin TX 78758-3117 > > > > _______________________________________________ > > openwrt-users mailing list > > [email protected] > > https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-users > > > _______________________________________________ > openwrt-users mailing list > [email protected] > https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-users -- Paul Elliott 1(512)837-1096 [email protected] PMB 181, 11900 Metric Blvd Suite J http://www.free.blackpatchpanel.com/pme/ Austin TX 78758-3117
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