In embedded systems, code size and dynamic instruction count are important performance indicators of power consumption and execution time. However, the use of different compilers may result in large different performance values even if a target machine is the same. So, the compiler selection in the system development is very important. In this paper, we compare the performances of two popular compilers, GCC and LLVM in perspective of the code size and the dynamic instruction count for the EISC embedded processor.Our comparison shows that LLVM is good at optimizing calculation intensive benchmarks, and GCC performs register allocation and jump optimization better. Overall, the GCC compiler shows better performance in most EEMBC benchmarks about 18% on average in terms of dynamic instruction. Also, the compiled code size by GCC is smaller than that of LLVM by 4% on average.
Voltage scaling is known to be an efficient way of saving power and energy within a system, and large caches such as LLCs are good candidates for voltage scaling considering their constantly increasing size. However, the V
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problem, in which the lower bound of scalable voltage is limited by process variation, has made it difficult to exploit the benefits of voltage scaling. Lowering V
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incurs multibit faults, which cannot be efficiently resolved by current technologies due to their high complexity and power consumption. We overcame the limitation by exploiting the data redundancy of memory hierarchy. For example, cache coherence states and several layers of cache organization naturally expose the existence of redundancy within cache blocks. If blocks have redundant copies, their V
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can be lowered; although more faults can occur in the blocks, they can be efficiently detected by simple error detection codes and recovered by reloading the redundant copies. Our scheme requires only minor modifications to the existing cache design. We verified our proposal on a cycle accurate simulator with SPLASH-2 and PARSEC benchmark suites and found that the V
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of a 2MB L2 cache can be further lowered by 0.1V in 32nm technology with negligible degradation in performance. As a result, we could achieve 15.6% of reduction in dynamic power and 15.4% of reduction in static power compared to the previous minimum power.
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