SAPHO—Scalable-Architecture Processor for Hardware Optimization: An FPGA Customizable Implementation Approach

Abstract

Soft-core processors are increasingly used in field-programmable gate arrays (FPGAs) to implement complex functions at critical points in embedded systems, where a pure firmware solution would require excessive development effort or hardware resources. However, most existing processors rely on fixed architectures, allocating the same amount of logic resources regardless of application requirements. This often leads to hardware over-provisioning, oversized data word lengths, and unnecessary power consumption. To address these limitations, this work presents SAPHO, a self-scalable processor that automatically adjusts its program and data memories, as well as its arithmetic and logic circuits, according to software requirements. This design paradigm reduces hardware waste, lowers logic element utilization, and enables more energy-efficient execution compared to conventional soft-core processors. Additionally, SAPHO incorporates a combinational Arithmetic Logic Unit (ALU), configurable for fixed- or floating-point operations, ensuring the execution of one instruction per clock cycle without pipeline stalls. Performance evaluation shows that, compared to the widely used commercial soft-core processor NIOS II, SAPHO achieves lower hardware cost and shorter execution time while maintaining scalability and flexibility for different embedded applications. Experimental results indicate that SAPHO executes all arithmetic operations in a fixed sequence of 13 clock cycles, whereas equivalent operations on the NIOS II may require from tens to thousands of cycles depending on configuration and data type. In an 8-point FFT benchmark, SAPHO reduces execution time by 77.36% compared to the fastest NIOS II configuration. Furthermore, SAPHO requires fewer logic elements (LEs) and demonstrates lower dynamic core power consumption, with reductions ranging from 15% to 33% compared to NIOS II variants. These results confirm that SAPHO provides a more efficient solution in terms of hardware cost, performance, and energy consumption while preserving flexibility for embedded applications.