felixge/pidctrl — pull request #5 by PSUdaemon (2014-10-13 17:11:00+00:00)
Title: Reset windup

http://brettbeauregard.com/blog/2011/04/improving-the-beginner%E2%80%99s-pid-reset-windup/

This prevents the controller from giving an output value that is out of range and stops the integral term from "winding up."