  We report on the status of an ongoing effort by the RQCD and ALPHA
Collaborations, aimed at determining leptonic decay constants of charmed
mesons. Our analysis is based on large-volume ensembles generated within the
CLS effort, employing N_f=2+1 non-perturbatively O(a) improved Wilson quarks,
tree-level Symanzik-improved gauge action and open boundary conditions. The
ensembles cover lattice spacings from a ~ 0.09 fm to a ~ 0.05 fm, with pion
masses varied from 420 to 200 MeV. To extrapolate to the physical masses, we
follow both the 2m_l+m_s=const. and the m_s=const. lines in parameter space.
