Date: Thu, 25 Sep 2008 10:38:37 -0700 From: Jeremy Chadwick <koitsu@FreeBSD.org> To: Dieter <freebsd@sopwith.solgatos.com> Cc: freebsd-usb@freebsd.org, freebsd-alpha@freebsd.org, freebsd-hardware@freebsd.org Subject: Re: alpha/127248: System crashes when many (7) serial port terminals (vt320-vt510) connected to the server via com to usb adapter and 2-usb hubs. Message-ID: <20080925173837.GA3415@icarus.home.lan> In-Reply-To: <200809251701.RAA18993@sopwith.solgatos.com> References: <20080925125417.GQ93308@cicely7.cicely.de> <200809251701.RAA18993@sopwith.solgatos.com>
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On Thu, Sep 25, 2008 at 10:01:51AM +0100, Dieter wrote: > [ -usb@ added to existing thread ] > > > > > 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. > > > > > > Many things about USB are crap (thanks, inthell), but if a USB to RS-232 > > > bridge cannot handle normal spikes and ground loops, I'd blame the > > > bridge, not USB itself. If the problem is spikes and ground loops > > > there is probably some RS-232 filter/isolator available to clean them > > > up. There could be a bug in the bridge which needs a software workaround. > > > In any case the system shouldn't crash. > > > > > > Are there specific make&model USB to RS-232 bridges that people > > > have had good luck with? > > > > USB can't handle spikes and ground loops. > > As said: use isolated devices, so you don't have the loops and spikes. > > You can blame the device for not being isolated, but you expect every > > device to provide expensive workaround for a design failure. > > USB is designed for cheap stuff - that's all about it. > > Surely a "good" USB to RS-232 bridge (if one exists?) or a RS-232 > filter/isolator (assuming they exist?) would be *far* less expensive > than the server class alpha you suggest below. I'm coming into this conversation late, so my apologies. If by "bridge" you mean a USB adapter that supports RS232 serial, then yes, there are some which work quite nicely with FreeBSD. 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. I can refer you to numerous people who have spoken to me privately or publicly on lists, praising the Prolific stuff. I have no idea if this driver works on Alphas. -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |
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