We propose a scheme to achieve controllable self-pulsing operation in a semiconductor photonic-crystal nanolaser. The scheme is based on coupling two asymmetric nanocavities and pumping only one of them. As a result, either periodic or chaotic subnanosecond Q-switched pulses can emerge. A coupled-mode approach is used to model the system and study the bifurcation diagram. An experimental realization is proposed on the basis of two evanescently coupled photonic-crystal nanocavities.