default do_zs to 1 and orbits_per_packet to x0001
initialise do_zs to 1 and orbits_per_packet to x0001 so that we don't crash DMA with do_zs=0 at startup
initialise do_zs to 1 and orbits_per_packet to x0001 so that we don't crash DMA with do_zs=0 at startup