We discuss a kinetically constraint asymmetric simple exclusion process on the
finite one-dimensional torus with $L$ sites. Jumps on a neighbouring pair of sites $(k,k+1)$ with rates 1 to the left and $q$ to the right can only happen if site $k-1$ is empty. This kinetic constraint is shown to lead to a breaking up of the state space into many disconnected ergodic components for more than half-filling, exactly two ergodic components at half filling, and irreducibility for less than half-filling. At half-filling the invariant measure is the exponential of the area under a random walk excursion with $L$ steps conditioned on returning to the origin. In this case a completely disordered phase with uniform measure and mean area $A\propto L^{3/2}$ for $q=1$ separates a phase-separated state ($q>1$) with mean area $A\propto L^{2}$ from a flat phase ($q<1$) with mean area $A\propto L$. Similar phase transitions persist in the weakly asymmetric regime where $q=\exp{(b/L^\alpha)}$ up to $\alpha=1$. The nature of these phase transitions
and the behavior for less than half-filling are open problems. (joint work with A. Zahra)