IGS_CLOCK_REF
M = ((target * (N + 1) * IGS_SCALE(P) + (IGS_CLOCK_REF/2)) +
IGS_CLOCK_REF/2) / IGS_CLOCK_REF - 1;
((IGS_CLOCK_REF * ((m) + 1)) / (((n) + 1) * IGS_SCALE(p)))