[Greg McKaskle]

The watchdog monitors one thing and controls another.

In the case of the system watchdog, it monitors incoming control packets and controls the outputs of the robot. The deadline is 100ms, and this means that if the incoming packets take longer than 100ms to arrive, the watchdog shuts down the outputs. As an example, lets say that the driver sets the tethered robot to driving forward, and then the clumsy mentor steps on the enet cable, yanking out out of the laptop. Since this breaks comms, the watchdog notices and will shutdown the outputs. Same situation if your laptop runs out of power, you shut down the radio, you yank the enet from the dlink, you lose power to the dlink, etc. If the cRIO doesn't get incoming packets, you don't want the robot to keep driving, and the system watchdog does that.

For the User watchdog, it observes your code's ability to call the feed function. If your code doesn't call feed, it shuts down the outputs. As an example, lets say that the robot is driving forward, and the forgetful mentor sets a breakpoint in your teleop function. Without the watchdog, the robot will maintain its current course. With the watchdog, it will halt the motors.

The Safety Timers are similar to this, but are I/O specific. They observe the updates to a given output and will shutdown that output if the deadline is missed. Again, this could be due to a breakpoint, delay, infinite loop, dead thread, bad logic, etc.

Does that help?
Greg McKaskle