Date: Tue, 19 Jan 2010 17:06:52 PST From: Dieter <freebsd@sopwith.solgatos.com> To: freebsd-hardware@freebsd.org Subject: Re: Multiple serial consoles via null modem cable Message-ID: <201001200106.BAA15886@sopwith.solgatos.com> In-Reply-To: Your message of "Fri, 15 Jan 2010 08:34:17 %2B0200." <717f7a3e1001142234y1de7ae15x6853e3ddcab4add9@mail.gmail.com>
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>From another thread awhile back, Jeremy Chadwick wrote: ] Anything that ] uses a Prolific chip will work well (supports custom serial rates, and ] does not drop/lose characters). The uplcom(4) driver is for this chip, ] and the man page lists off some consumer models/devices available. Also from the thread awhile back, Bernd Walter wrote: } This is because USB is absolutely crap for this purpose. } RS232 terminals, especially with long cables, can produce several kind } of spikes and ground loops, which USB is very very sensitive about. } The upcoming new USB stack does a lot about handling transmission } errors, but the underlying problem is USB and not FreeBSD. } The best thing software can do about this is avoiding the panics. } Nevertheless the new USB stack is likely not being merged into any alpha } supporting OS release, so even that will not happen for alpha. } } My advise is to use a completely other technology to connect the terminals. } A galvanic isolated USB device might work, but there are lot of PCI and } Ethernet devices on the market which are more solid by design than USB. If different systems are on different UPSs it might create a ground loop? If necessary, you can optically isolate the RS-232 line, which should fix the problem. http://www.rs232-converters.com/opto-isolated_converters/Opto-Isolated_RS232_RS485_RS422_Isolators.htm I have not actually tried this. This is just an example of the isolators available, not a recommendation for this specific product or vender. Google can find similar products.
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