Control of Event Handling Timeliness in RTEMS

1 Embedded real-time applications that interact with the outside environment may be subjected to temporal uncertainty due to the potential asynchronous characteristics of events. If event handling, which is usually associated with interrupts, is not carefully controlled, overload scenarios can cause application tasks to miss deadlines, with severe consequences. In this paper we address the problem of controlling event handling timeliness, by enhancing the real-time multitasking kernel RTEMS with components to characterize event rate, decide if there is an overload situation, and switch between an interrupt mode and a polling mode event handling. This is done with minimal impact on the existing application, by replacing the interrupt handler by another one that implements those control mechanisms before calling the original application interrupt service routine. A case study using the keyboard as the input device is presented, and implementation issues are discussed.