In this paper we examine analytically the large-N gap equation and its solution for the 2D CP N −1 sigma model defined on a Euclidean spacetime torus of arbitrary shape and size (L, β), β being the inverse temperature. It is shown that the system has a unique homogeneous phase, with the CP N −1 fields n i acquiring a dynamically generated mass λ ≥ Λ 2 (analogous to the mass gap of SU (N ) Yang-Mills theory in 4D), for any β and L. We comment on several related topics discussed in the recent literature. One concerns the possibility, which we will exclude, of a "Higgs-like" -or deconfinement -phase at small L and at zero temperature. Another topic involves "soliton-like" (inhomogeneous) solutions of the generalized gap equation. In both cases, a proper treatment of the zero modes is essential. A related question concerns a possible instability of the standard CP N −1 vacuum on R 2 , which is shown not to occur. The CP N −1 model with twisted boundary conditions is also analyzed. The θ dependence, and different limits involving N , β and L are briefly discussed.