A time-predictable VLIW processor and its compiler support

Time predictability is an important requirement for real-time embedded application domains such as automotive, air transportation, and multimedia processing. However, the architectural design of modern microprocessors mainly concentrates on improving the average-case performance, which can significantly compromise the time predictability and can make accurate worst-case performance analysis extremely difficult if not impossible. This paper studies the time predictability of VLIW (Very Long Instruction Word) processors and its compiler support. We analyze the impediments to time predictability for VLIW processors and propose compiler-based techniques to address these problems with minimal disturbance on the VLIW hardware design. The VLIW compiler is enhanced to support full if conversion, hyperblock scheduling, and intra-block nop insertion to enable efficient WCET (Worst Case Execution Time) analysis for VLIW processors. Our experiments indicate that the time-predictability of VLIW processor can be improved significantly.