  To any solution of a linear system of differential equations, we associate a
kernel, correlators satisfying a set of loop equations, and in presence of
isomonodromic parameters, a Tau function. We then study their semiclassical
expansion (WKB type expansion in powers of the weight hbar per derivative) of
these quantities. When this expansion is of topological type (TT), the
coefficients of expansions are computed by the topological recursion with
initial data given by the semiclassical spectral curve of the linear system.
This provides an efficient algorithm to compute them at least when the
semiclassical spectral curve is of genus 0. TT is a non trivial property, and
it is an open problem to find a criterion which guarantees it is satisfied. We
prove TT and illustrate our construction for the linear systems associated to
the q-th reductions of KP - which contain the (p,q) models as a specialization.
