Kindle digital photo frame part 3: Changing screensavers every 3 hours

Getting the Kindle to change its screensaver is as simple as running /usr/bin/powerd_test -p twice. The script to do so:

I wanted the screensaver to be changed every 3 hours, excluding nighttime. It's a matter of appending to /etc/crontab/root:

Then I ran into a pesky problem. The screensaver changer works if I ran it manually. It doesn't work via the cron job. Or rather, I discovered that the Kindle goes to sleep after 1 minute in screensaver mode.

After fiddling with /usr/bin/powerd_test -s for quite some time I discovered the following. The Kindle has 4 power levels: Active, Screen Saver, Ready to suspend, and sleep. Active stays on for 10 minutes, Screen Saver stays on for 1 minute, and Ready to suspend stays on for 5 seconds. This is my log:

I can wake up my Kindle via the command "lipc-set-prop com.lab126.powerd wakeUp 1" provided it is in one of those 3 states. To try and suspend my Kindle in the "ScreenSaver" or "Ready to suspend" state for as long as possible, I investigated the seemingly useless property, deferSuspend, from com.lab126.powerd. When you run it, it gives the error:

com.lab126.powerd failed to set value for property deferSuspend (0x8 lipcErrNoSuchProperty)

I discovered that the property can only be set DURING THE READY TO SUSPEND STATE. That means after 11 minutes of leaving the Kindle alone I have a 5 second window to change the time left in "Ready to Suspend" state. See my logs:

My screensaver changing script ended up as: