CIFER: A Cache-Coherent 12nm 16mm2 SoC With Four 64-Bit RISC-V Application Cores, 18 32-Bit RISC-V Compute Cores, and a 1541 LUT6/mm2 Synthesizable eFPGA

This paper presents CIFER, the world's first opensource, fully cache-coherent, heterogeneous many-core, CPU-FPGA SoC. The 12nm, 16mm2 chip integrates four 64-bit, OS-capable, RISC-V application cores; three TinyCore clusters that each contain six 32-bit, RISC-V compute cores (18 in total); and an EDA-synthesized, standard-cell-based eFPGA. CIFER enables the decomposition of real-world applications and tailored execution (parallelization or specialization) per decomposed task. Our evaluation shows that: 1) the TinyCore clusters increase the throughput and energy efficiency of data-and thread-parallel tasks by up to 7.95× and 7.75× over one 64-bit core, respectively; 2) the eFPGA increases the throughput and energy efficiency of hardware-accelerable tasks by up to 9.29× and 10.62×, respectively; 3) using coherent caches for data transfer between the processors and the eFPGA increases the throughput and energy efficiency by up to 11.1× and 10.5×, respectively.