Architectural Support for Embedded Operating Systems

Title of Thesis: ARCHITECTURAL SUPPORT FOR EMBEDDED OPERATING SYSTEMS Degree candidate: Brinda Ganesh Degree and year: Master of Science, 2002 Thesis directed by: Professor Bruce L. Jacob Department of Electrical and Computer Engineering This thesis investigates hardware support for managing time, events, and process scheduling in embedded operating systems. An otherwise normal content-addressable memory that is tailored to handle the most basic functions of a typical RTOS, the CCAM (configurable content-addressable memory) turns what are usually O(n) tasks into O(1) tasks using the parallelism inherent in a hardware search implementation. The mechanism is modelled in the context of the MCORE embedded microarchitecture, several variations upon μC/OS-II, a popular open-source real-time operating system and Echidna, a commercial real-time operating system. The mechanism improves the real-time behavior of systems by reducing the overhead of the RTOS by 20% and in some cases reduces energy consumption 25%. This latter feature is due to the reduced number of instructions fetched and executed, even though the energy cost of one CCAM access is much higher than the energy cost of a single instruction. The performance and energy benefits come with a modest price: an increase in die area of roughly 10%. The CCAM is orthogonal to the instruction set (it is accessed via memorymapped I/O load/store instructions) and offers features used by most RTOSes. ARCHITECTURAL SUPPORT FOR EMBEDDED OPERATING SYSTEMS