This is a quick update. I've been running the home monitor program for around a week on the Beaglebone embedded Linux (Angstrom) system, with the Option Icon modem connected via a powered USB hub, and the board entirely on its own. "On its own" means not connected to the network or the host USB bus on the PC, so it cannot communicate other than via SMS (text) messaging. It has not stopped by itself yet, so it appears very likely that the USB power was an issue in earlier failures.
It starts automatically on reboot (power cycling.) I have set a crontab job (shell script) scheduled for @reboot, that runs the tclsh interpreter on my monitor program after an initial 120 second delay after reboot to let the GSM modem be recognized by the OS.
In testing, I have temporarily interrupted power to both the powered hub and board to make sure it restarts OK, and no problems yet. This is important since if I'm away and it fails I can simply have someone cycle power to get it going. Also, I can build a simple external "keep-alive" circuit the monitor program must periodically 'ping' with a GPIO bit level change. In the absence of the pulse the circuit will cause power to be recycled via maybe a relay (optically isolated, naturally.)
Of course Beaglebone also cannot set its clock since it has no internal battery-backed clock, so I'll have to figure out a way of doing this. Maybe by having it send itself a text message, and getting the time from the received message.
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