Am Dienstag, 21. Juni 2005 04:46 schrieb Paul Alfille:
> On Monday 20 June 2005 04:38 pm, Jan Kandziora wrote:
> > Dear Paul,
> >
> > I've investigated further on the problem I described last week (in the
> > thread "owtcl and writing data").
> >
> > It seems to be related to EMC: Nearly every time I switch on a large
> > 240/24V AC transformer I need for my project, I get a single error of the
> > kind I described. But sometimes, it is even a cascade of such errors,
> > which I can't bring into connection to any action I took (not). Maybe, it
> > was the fluorescent light on last week, but today, I didn't turn them on
> > and still got cascades of such errors (over about 1 minute).
> >
> > Then again, everything is fine for a couple of minutes.
>
> Is it possible to add shielding?
>
From overall engineering point of view, shielding makes things worse.
Cables are thicker and harder to bend, heat is dissipated worse and even then,
there is no guarantee you won't encounter any problems - There is hardly any
shielding that could withstand a large electromagnetic pulse sent by a mains
transformator or other impedance switched on at maximum voltage of the sine
wave. To allow this, the shielding has to be connected to earth with a
maximum resistance about 1 milliohms, which rules out any kind of connectors
(and most kinds of earth, too).
This is a general problem. All better transmission protocols have some
retry-funtion, if such a situation happens - which is often.
> > I checked for USB errors with dmesg, and got very few USB disconnects
> > (about 1 of 30 times), but no other USB link layer errors. On the most
> > tries, only the 1-wire seemed to be affected.
>
> The question is what is the program/port's state after one of these errors.
> It seems like there is nor recovery after an error. (i.e., the system
> doesn't work intermittently, only yes or no). If the error causes the USB
> port to close, life is easy.
>
I tried about 70..80 switches, only 2 times the USB connection broke; most
times, the 1-wire connection broke; sometimes, nothing happened (must have
switched on near zero-cross)
> We can re-open the USB port more easily than a full restart. We don't need
> to enumerate the devices, or resort the internal data structures.
>
Ok. That would bring down the recovery time for usb fail to the values for
recovery of 1-wire.
> >
> > 1. Is there any way to detect an "unrecoverable" error on bus side?
> > 2. I want to use owserver. You offered to change owserver to restart the
> > connection automatically: How is the development status for this?
> > 3. Is there any way to process the init sequence faster? For USB errors,
> > it would not be so dramatic if it takes 3 to 5 seconds to recover, as I
> > expect them to be very rare. However, the 1-Wire error happens *every
> > time* a big inductive load is switched near the device, so a faster
> > recovery would be a big help.
>
> Ho do I tell the "1-wire error" from normal failures? (Wrong addresses,
> bits lost, ...)
>
All the device nodes in the mnt/1wire/uncached directory are gone in that
case, even the one for the adaptor chip! owserver just fails in that
situation. I think there already is a function that "cleans up" that
directory or exit()s owserver.
Kind regards
Jan
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