Almost all multicore processors use a shared-memory architecture due to its simple programming model. Recently, however, the message-passing mechanism is also drawing attention due to its potentially better scalability. In this work, we demonstrate that a hybrid communication mechanism supporting both message passing and shared memory can provide both higher performance and energy efficiency. This 16-core processor has 3 key features: (1) A cluster-based hierarchical architecture supporting both shared-memory and message-passing communication. (2) A cache-free memory hierarchy with an extended register file, small private memory and moderate shared memory to avoid complex cache coherence issues and achieve high energy efficiency by keeping data accesses local. (3) A hardware-aided mailbox mechanism to accelerate the synchronization procedure between different processor nodes. With these techniques, our multicore processor can provide high performance for many applications. Chip test results show that its maximum clock frequency is 800MHz and typical power consumption is 320mW, when running basic applications with clock gating at 1.2V at room temperature.
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