Minimum Movement
Despite whatever penalties to your speed you might have, as long as you can move at all you can take a full action to move 5 feet (1 square) in any direction, even diagonally. This rule doesn’t allow you to move through impassable terrain or to move when all movement is prohibited. Such movement provokes attacks of opportunity as normal (despite the distance covered, this move isn’t a guarded step).
Source
Core Rulebook pg. 257
