  We carry out a comprehensive analysis of the simplest curvaton model, which
is based on two non-interacting massive fields. Our analysis encompasses cases
where the inflaton and curvaton both contribute to observable perturbations,
and where the curvaton itself drives a second period of inflation. We consider
both power spectrum and non-Gaussianity observables, and focus on presenting
constraints in model parameter space. The fully curvaton-dominated regime is in
some tension with observational data, while an admixture of inflaton-generated
perturbations improves the fit. The inflating curvaton regime mimics the
predictions of Nflation. Some parts of parameter space permitted by power
spectrum data are excluded by non-Gaussianity constraints. The recent BICEP2
results [1] require that the inflaton perturbations provide a significant
fraction of the total perturbation, ruling out the usual curvaton scenario in
which the inflaton perturbations are negligible, though not the admixture
regime where both inflaton and curvaton contribute to the spectrum.
