From: James Sentman <james-AT-sentman.com>
Date: 17 Jun 2009 08:38:59 UTC   (11:38:59 AM in author's locale)
To: xtensionlist-AT-shed.com

On Jun 15, 2009, at 7:32 PM, Doug Kiekow wrote:

> It would be nice to know how this part works. I've seen log messages
> about USB problems, and XTension's attempts to restart. But if I
> remember correctly there is a specific number of retries. Does
> XTension then just give up, or does it retry again at a later time?

I think the default retry is 5 times, after which XTension will run a
global script named "Interface Error Script" (if you have created one,
the name is in the popup menu in the new script naming sheet) and set
the "ThisInterface" value to the name of the interface which it's
given up on. You can then decide to try to set the enabled property of
the interface back to true to retry another 5 times or to send some
alert or something else.

You can also change the number of retries from the command line (in
xtension, not the terminal command line) by doing a

set retries of xInterface "name of your interface" to 10000

or some other number, that setting is saved in the dictionary and it
is not necessary to set it at every startup or interface init.

>
> This all becomes important in trying to figure out how to power the
> system assuming there will be outages. My serial devices (CM11 and
> several W800) come off a powered USB hub. Do I need to provide
> backup power to that hub along with the computer? Or better yet is
> there a script that would retry the USB when line voltage returns?

There is a difference between loosing a connection to an interface and
not being able to establish one or having the USB cable pulled. An
interface should not quit or crash if power is lost at the interface.
Eventually the background app will figure out that the interface is
not responding and will send you a loss of power error message that
you can also trap. But it will reconnect to the interface by itself
when power is restored. That is different than a disconnection error.

the crashes that you see if they are due to USB errors you really do
need to fix as these can come so fast together as to cause a kernel
panic to the overall machine and not just the XTension handler. A bad
USB hub or a bad cable or a ground loop or something can cause the bus
to dump everything off, causing the kext handlers or drivers to unload
and then reload immediately. Like plugging and unplugging a USB device
as fast as you can and we all know thats bad. just doing this can
cause the whole machine to panic (something that never happened with a
regular old serial port thank you very much progress) But again, the
rs232 usb/serial devices have potentially better drivers than X10 usb
interfaces simply because of the sheer number of people using them. So
I would trust the FTDI chip drivers to handle all of this better than
a custom X10 device driver no matter how much it may pretend to be an
interface device.

Thanks,
James

James Sentman sentman.com MacHomeAutomation.com


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