An 8640 MIPS SoC with Independent Power-Off Control of 8 CPUs and 8 RAMs by An Automatic Parallelizing Compiler

Power efficient SoC design for embedded applications requires several independent power-domains where the power of unused blocks can be turned off. An SoC for mobile phones defines 23 hierarchical power domains but most of the power domains are assigned for peripheral IPs that mainly use low-leakage high-V_t transistors. Since high-performance multiprocessor SoCs use leaky low-V_t transistors for CPU sections, leakage power savings of these CPU sections is a primary objective. We develop an SoC with 8 processor cores and 8 user RAMs (1 per core) targeted for power-efficient high-performance embedded applications. We assign these 16 blocks to separate power domains so that they can be independently be powered off. A resume mode is also introduced where the power of the CPU is off and the user RAM is on for fast resume operation. An automatic parallelizing compiler schedules tasks for each CPU core and also performs power management for each CPU core. With the help of this compiler, each processor core can operate at a different frequency or even dynamically stop the clock to maintain processing performance while reducing average operating power consumption. The compiler also executes power-off control of unnecessary CPU cores.