The first phase of a heavy quark program based on twisted mass valence quarks has been presented at last years's lattice conference. The CLS Nf=2+1 ensembles were used for their fine lattice spacing, while twisting the masses is expected to reduce discretisation errors even further and allow for a fully relativistic calculation. We present our strategy and preliminary results on three point functions, corresponding to D→K and D→π semileptonic decays. The form factors for mu=md=ms quark masses obtained as a first step are shown here to be at the percent level in statistical precision at q2=0.
