Date: Thu, 25 Sep 2008 10:01:51 +0100 From: Dieter <freebsd@sopwith.solgatos.com> To: freebsd-alpha@freebsd.org, freebsd-hardware@freebsd.org, freebsd-usb@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: <200809251701.RAA18993@sopwith.solgatos.com> In-Reply-To: Your message of "Thu, 25 Sep 2008 14:54:17 %2B0200." <20080925125417.GQ93308@cicely7.cicely.de>
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[ -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. And IIRC it is just speculation that the original poster's problem is caused by spikes or ground loops. > Yes - the system shouldn't crash, but don't expect it ever being fixed > for FreeBSD-alpha. There is a 6.4 coming out, yes? It is unlikely that the problem is alpha specific. If an alpha crashes, other archs will likely crash. > > > 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. > > > > The problem with PCI is the limited number of slots. :-( > > Well - not realy with server class alphas... In my world, a "server" means 1-4 full height 19" racks with quite large price tags and power&cooling requirements. Some people think a server is a pee-cee. So I'm not sure what you mean by "server class alphas". I have what I would call a "workstation" class alpha, which cost an obscene amount to get 6 PCI slots instead of 4, and at times they are all full. So I can't use up a slot just to get a couple more RS-232 ports. How many PCI slots does a server class alpha have? RS-232 doesn't require PCI levels of bandwidth. Something like a USB to RS-232 bridge could be a good solution, if I knew which make&model of bridge worked well with *BSD. Poking around on the web I can't even find what chip they have inside. Do these bridges actually work properly, or do they have gotchas like the USB to SATA/PATA bridges? > > Ethernet could be a good solution for some applications, if you > > can get the software to deal with it. NFS is crap, *real* distributed > > file systems handled devices transparently. (thanks, Sun) > > This is a different topic. > For RS232 Ethernet is quite reasonable. For some applications yes. But some apps want to open /dev/ttyXX and do ioctls on it. How does one use such an app on Free/Net/OpenBSD with the RS-232 device on some Ethernet connected RS-232 port? > > Does anyone make firewire to RS-232 bridges? > > Or stay with the old DEC devices - they are rock solid even after all > those years. It is not obvious what "old DEC devices" you are referring to.
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