jwatte:
Now, the main problem is I'd really like it to not reset when I open the serial device. That probably requires custom firmware, and I'm going to have to go spelunking for a while. Maybe it actually isn't worth it; a fresh reset now and then might clear out the cobwebs or something
Disable the auto reset with a 1-10 uF capacitor across GND & Reset ? That what I do, it beats faffing about with software fudges.