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Looping operations impose a significant bottleneck to achieving better computational efficiency for embedded applications. In this paper, a novel zero-overhead loop controller (ZOLC) supporting arbitrary loop structures with multiple-entry and multiple-exit nodes is described and utilized to enhance embedded RISC processors. A graph formalism is introduced for representing the loop structure of application programs, which can assist in ZOLC code synthesis. Also, a portable description of a ZOLC component is given in detail, which can be exploited in the scope of RTL synthesis for enabling its utilization. This description is designed to be easily retargetable to single-issue RISC processors, requiring only minimal effort for this task. The ZOLC unit has been incorporated to different RISC processor models and research ASIPs at different abstraction levels (RTL VHDL and ArchC) to provide effective means for low-overhead looping without negative impact to the processor cycle time. Average performance improvements of 25.5% and 44% are feasible for a set of kernel benchmarks on an embedded RISC and an application-specific processor, respectively. A corresponding 10% speedup is achieved on the same RISC for a subset of MiBench applications, not necessarily featuring the examined performance-critical kernels.
Microprocessors, Control design, Pipeline processors, Optimization, Real-time and embedded systems, Hardware description languages

N. Kavvadias and S. Nikolaidis, "Elimination of Overhead Operations in Complex Loop Structures for Embedded Microprocessors," in IEEE Transactions on Computers, vol. 57, no. , pp. 200-214, 2007.
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