  We consider the problem of frequency estimation by observations of the
periodic diffusion process possesing ergodic properties in two different
situations. The first one corresponds to continuously differentiable with
respect to parameter trend coefficient and the second - to discontinuous trend
coefficient. It is shown that in the first case the maximum likelihood and
bayesian estimators are asymptotically normal with rate $T^{3/2}$ and in the
second case these estimators have different limit distributions with the rate
$T^2$.
