rocket-chip/rocket

Rocket Core Generator

Rocket is a 6-stage single-issue in-order pipeline that executes the 64-bit scalar RISC-V ISA. Rocket implements an MMU that supports page-based virtual memory and is able to boot modern operating systems such as Linux. Rocket also has an optional IEEE 754-2008-compliant FPU, which implements both single- and double-precision floating-point operations, including fused multiply-add.

We plan to open-source our Rocket core generator written in Chisel in the near future. We are currently in the process of cleaning up the repository. Please stay tuned.

Currently, a Rocket core with an 8 KB direct-mapped L1 instruction cache and an 8 KB direct-mapped L1 data cache has been instantiated and committed to the fpga-zynq infrastructure repository. A copy of the generated Verilog is available here.

The following table compares a 32-bit ARM Cortex-A5 core to a 64-bit RISC-V Rocket core built in the same TSMC process (40GPLUS). Fourth column is the ratio of RISC-V Rocket to ARM Cortex-A5. Both use single-instruction-issue, in-order pipelines, yet the RISC-V core is faster, smaller, and uses less power.

ISA/Implementation	ARM Cortex-A5	RISC-V Rocket	R/A
ISA Register Width	32 bits	64 bits	2
Frequency	>1 GHz	>1 GHz	1
Dhrystone Performance	1.57 DMIPS/MHz	1.72 DMIPS/MHz	1.1
Area excluding caches	0.27 mm2	0.14 mm2	0.5
Area with 16KB caches	0.53 mm2	0.39 mm2	0.7
Area Efficiency	2.96 DMIPS/MHz/mm2	4.41 DMIPS/MHz/mm2	1.5
Dynamic Power	<0.08 mW/MHz	0.034 mW/MHz	>= 0.4