Methods and apparatus to control power state transitions in embedded
systems are disclosed. In a disclosed method, power state transitions of
agents in the system are managed by a central authority. The agents
register themselves with the central authority. When a request to
transition the system to a requested power state is received, the central
authority issues callback instructions to the agents in the system that
support the requested power state. The callback instructions are issued
in a temporal order indicated by the power state dependencies of the
agents. Thus, the central authority arbitrates the order in which the
agents transition to the requested power state. The power state
dependencies of the agents are registered with the central authority by
the agents either at power-up of the system or when the agents are
plugged into the system.