  We present results of lattice QCD simulations with mass-degenerate up and
down and mass-split strange and charm (Nf=2+1+1) dynamical quarks using Wilson
twisted mass fermions at maximal twist. The tuning of the strange and charm
quark masses is performed at three values of the lattice spacing a~0.06 fm,
a~0.08 fm and a~0.09 fm with lattice sizes ranging from L~1.9 fm to L~3.9 fm.
We perform a preliminary study of SU(2) chiral perturbation theory by combining
our lattice data from these three values of the lattice spacing.
