thanks – actually the RTC was set up. But it turns out the real cause of the problem was apparently just a poor or intermittent connection between the Pi and the Open Sprinkler board. One of the ribbon cable connectors apparently wasn’t seated correctly or there was some dirt on one of the contacts. I reseated it, and everything seems to be working fine now :-). I’m still seeing the “UU” entries in the output of i2cdetect, but I believe this is because these devices are in use by the program so show up as “Unavailable”.
BTW I also was having problems with the pi sometimes losing its wifi connection, and not re-connecting – found the “wicd-curses” package and would strongly recommend it to anyone having similar problems (or just to simplify setting up wifi on the pi):
http://windowslinuxcommands.blogspot.com/2013/06/raspberry-pis-new-wifi-manager-friend.html
my next project is to figure out the best way to connect my existing rain sensor (its just a NC switch that opens when it gets wet) to the pi/OSPI board, and integrate it with sprinklers_pi code.
regards
Don