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.

[Wilko Bulte]

Quoting Bernd Walter, who wrote on Thu, Sep 25, 2008 at 02:54:17PM +0200 ..
> 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.

20mA current loop comes to mind

> > > 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...

Yeah... a Turbolaser running a terminal server 8-)

> > Does anyone make firewire to RS-232 bridges?
> 
> Or stay with the old DEC devices - they are rock solid even after all
> those years.

DECserver900 are indeed rock solid.  Run reverse-telnet driven bij conserver
on FreeBSD.  Works like a charm.  I still have a considerable # of lines
like that running in an engineering lab.  conserver runs on Tru64 in that
particular case.

Wilko