Date: Sat, 20 Sep 2008 14:54:14 +0200 From: Bernd Walter <ticso@cicely7.cicely.de> To: gavin@freebsd.org Cc: freebsd-alpha@freebsd.org, alexey@zhtw.org.ru 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: <20080920125414.GS93308@cicely7.cicely.de> In-Reply-To: <200809101624.m8AGOHdS047064@freefall.freebsd.org> References: <200809101624.m8AGOHdS047064@freefall.freebsd.org>
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On Wed, Sep 10, 2008 at 04:24:17PM +0000, gavin@freebsd.org wrote: > Synopsis: System crashes when many (7) serial port terminals (vt320-vt510) connected to the server via com to usb adapter and 2-usb hubs. > > State-Changed-From-To: open->feedback > State-Changed-By: gavin > State-Changed-When: Wed Sep 10 16:17:30 UTC 2008 > State-Changed-Why: > To submitter: Are you able to compile the debugger into the kernel > and obtain a backtrace next time it panics? > > Add the following to your kernel config file: > options KDB > options DDB > options GDB > > Then when the machine crashes next, enter "bt" at the prompt? > (Disclaimer: I've never used FreeBSD/alpha before, but this should work) > > By the way, my gut instinct is that this panic is caused by the fact the > serial dongles seem to be disconnecting/reconnecting, and not specifically > because the machine is an Alpha. However, why they are disconnecting in > the first place, I don't know. 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. -- B.Walter <bernd@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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