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

This letter presents CIFER, the world’s first open-source, fully cache-coherent, heterogeneous many-core, CPU-FPGA system-on-chips. The 12 nm, 16-mm2 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 electronic design automation-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\times $ and $7.75\times $ over one 64-bit core, respectively; 2) the eFPGA increases the throughput and energy efficiency of hardware-accelerable tasks by up to $9.29\times $ and $10.62\times $ , respectively; and 3) using coherent caches for data transfer between the processors and the eFPGA increases the throughput and energy efficiency by up to $11.1\times $ and $10.5\times $ , respectively.