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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. Jeremy Chadwick Thu Sep 25 11:01:35 2008

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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