Date: Thu, 25 Sep 2008 14:54:17 +0200 From: Bernd Walter <ticso@cicely7.cicely.de> To: Dieter <freebsd@sopwith.solgatos.com> Cc: 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: <20080925125417.GQ93308@cicely7.cicely.de> In-Reply-To: <200809201655.QAA10313@sopwith.solgatos.com> References: <20080920125414.GS93308@cicely7.cicely.de> <200809201655.QAA10313@sopwith.solgatos.com>
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On Sat, Sep 20, 2008 at 09:55:59AM +0100, Dieter wrote: > [ -hardware@ list added to existing -alpha@ thread as this > doesn't seem to be alpha specific ] > > > 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. Yes - the system shouldn't crash, but don't expect it ever being fixed for FreeBSD-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. > > The problem with PCI is the limited number of slots. :-( Well - not realy with server class alphas... > 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. > Does anyone make firewire to RS-232 bridges? Or stay with the old DEC devices - they are rock solid even after all those years. -- B.Walter <bernd@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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