How Rebound! works
Rebound! uses the PowerKey hardware and software to do its job. The Rebound! control panel lets you change settings stored in the PowerKey background software, which programs the PowerKey hardware to actually respond to crashes.
Detecting system crashes
The PowerKey software runs in the background constantly, monitoring your system by periodically communicating with the PowerKey hardware. Every few seconds, the software resets a "system timer" in the hardware, which then counts down each second. As long as the system is running normally, the software will keep resetting this timer, and it will never reach zero.
If the system crashes, the software will stop running, and won't be able to reset the system timer. When the timer reaches zero, the hardware will attempt to restart the computer.
The hardware restarts the computer by first switching off its power outlet to turn the computer off. A few seconds later, it turns its power outlet back on, then sends the 'on' signal on the USB port, just as if you'd pressed it on a keyboard.
Note: Newer models of Macintosh (notably iMacs made since September 2000, and G4s made since September 2002) do not support keyboard startup. For these models, you must set your Energy Saver control panel to restart after a power failure. See "Installing the software" in the PowerKey Help for more information.
Detecting application crashes
Rebound!'s application crash detection works in a similar manner as the system timers described above. An application with Rebound! support periodically resets an "application timer" in the PowerKey background software. If the application fails, its application timer will count down to zero. When it reaches zero, the software will respond.
Tip: You can see the application timers working in the "application crashes" section of the Rebound! control panel.
The PowerKey software will first initiate a Finder restart, and the Finder will attempt to quit all open applications. If this attempt fails (for example, if an application refuses to quit), the PowerKey software will initiate a "low-level" restart after one minute. Finally, if this fails, the PowerKey hardware will then perform a hard restart, after a delay specified by the "Restart if system doesn't respond" slider in the "System Crashes" panel.
A list of applications which support application timers can be found on our web site, or check with your application's developer to see if they support Rebound! Also, since Rebound! uses the same software as our popular Kick-off! product, any application which supports Kick-off! will automatically support Rebound! as well.
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