Execution Time Control: A hardware accelerated Ada implementation with novel support for interrupt handling
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Execution time control is a technique that allows execution time budgets to be set and overruns to be handled dynamically to prevent deadline misses. This removes the need for the worst-case execution time (WCET) of tasks to be found by offline timing analysis – a problem that can be very hard to solve for modern computer architectures. Execution time control can also increase the processor utilization, as the WCET will often be much higher than the average execution time. This thesis describes how the GNU Ada Compiler and a bare-board Ravenscar run-time environment were ported to the Atmel AVR32 UC3 microcontroller series making the Ada programming language available on this architecture for the first time, and an implementation of Ada execution time control for this system that supports full execution time control for interrupt handling. Usage patterns for this brand new feature are demonstrated in Ada by extending the object-oriented real-time framework with execution time servers for interrupt handling, allowing the system to be protected against unexpected bursts of interrupts that could otherwise result in deadline misses. Separate execution time measurement for interrupt handling also improves the accuracy of measurement for tasks. As a direct result of the work presented in this thesis separate execution time measurement for interrupts will be included in the forthcoming ISO-standard for Ada 2012. While the implementation of execution time control is for the Ada programming language and the UC3 microcontroller series, the design and implementation should be portable to other architectures, and the principles of execution time control for interrupt handling applicable to other programming languages. Low run-time overhead is important for execution time control to be useful for real-time systems. Therefore a hardware Time Management Unit (TMU) was designed to reduce the overhead of execution time control. This design has been implemented for the UC3 and performance tests with the developed run-time environment shows that it gives a significant reduction of overhead. The memory-mapped design of the TMU also allows it to be implemented on other architectures.
Består avGregertsen, Kristoffer Nyborg; Skavhaug, Amund. An efficient and deterministic multi-tasking run-time environment for Ada and the Ravenscar profile on the Atmel AVR (R) 32 UC3 microcontroller. DATE - 2009 DESIGN, AUTOMATION & TEST IN EUROPE CONFERENCE & EXHIBITION, VOLS 1-3: 1572-1575, 2009.
Gregertsen, Kristoffer Nyborg; Skavhaug, Amund. A real-time framework for Ada 2005 and the Ravenscar profile. 2009 35TH EUROMICRO CONFERENCE ON SOFTWARE ENGINEERING AND ADVANCED APPLICATIONS, PROCEEDINGS - : 515-522, 2009. 10.1109/SEAA.2009.40.
Gregertsen, Kristoffer Nyborg; Skavhaug, Amund. Execution-time management for interrupt handling. , 2009.
Gregertsen, Kristoffer Nyborg; Skavhaug, Amund. Implementing the new Ada 2005 timing event and execution time control features on the AVR32 architecture. Journal of systems architecture. (ISSN 1383-7621). 56(10): 509-522, 2010. 10.1016/j.sysarc.2010.08.001.
Gregertsen, Kristoffer Nyborg; Skavhaug, Amund. Implementation and Usage of the new Ada 2012 Execution Time Control Features. Ada User Journal. (ISSN 1381-6551). 32(4): 265-275, 2011.
Gregertsen, K. N.; Skavhaug, A.. Improving the performance of execution time control by using a hardware Time Management Unit. , 2012. 10.1007/978-3-642-30598-6_13.