Cyclic Sequence Generators as Program Counters for High-Speed FPGA-based Processors
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This paper compares the performance of conventional radix-2 program counters with program counters based on Feedback Shift Registers (FSRs), a class of cyclic sequence generator. FSR counters have constant time scaling with bit-width, N, whereas FPGA-based radix-2 counters typically have O(N) time-complexity due to the carry-chain. Program counter performance is measured by synthesis of standalone counter circuits, as well as synthesis of three FPGA-based processor designs modified to incorporate FSR program counters. Hybrid counters, combining both an FSR and a radix-2 counter, are presented as a solution to the potential cache-coherency issues of FSR program counters. Results show that high-speed processor designs benefit more from FSR program counters, allowing both greater operating frequency and the use of fewer logic resources.
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