  We perform an analysis of QCD lattice data on charmed meson masses. The
quark-mass dependence of the data set is used to gain information on the size
of counter terms of the chiral Lagrangian formulated with open-charm states
with J^P= 0^- and J^P =1^- quantum numbers. Of particular interest are those
counter terms that are active in the exotic flavour sextet channel. A chiral
expansion scheme where physical masses enter the extrapolation formulae is
developed and applied to the lattice data set. Good convergence properties are
demonstrated and an accurate reproduction of the lattice data based on
ensembles of PACS-CS, MILC, ETMC and HSC with pion and kaon masses smaller than
600 MeV is achieved. It is argued that a unique set of low-energy parameters is
obtainable only if additional information from HSC on some scattering
observables is included in our global fits. The elastic and inelastic s-wave pi
D and eta D scattering as considered by HSC is reproduced faithfully. Based on
such low-energy parameters we predict 15 phase shifts and in-elasticities at
physical quark masses but also for an additional HSC ensemble at smaller pion
mass. In addition we find a clear signal for a member of the exotic flavour
sextet states in the eta D channel, below the bar K D_s threshold. For the
isospin violating strong decay width of the D_{s0}(2317) we obtain the range
(104-116) keV.
