A method, system, and an apparatus for providing a therapy neurostimulation signal. The apparatus includes a sealed housing being of a total volume of less than about 14.5 cc and a power supply contained within the sealed housing. The power supply includes a charge capacity of at least about 100 milliAmpHours. The apparatus also includes a controller to control an operation of the power supply and to provide an electrical neurostimulation signal for stimulating a portion of a neural tissue. The apparatus also provides for implementing an interrupt-driven architecture into an implantable medical device.