Bluespec Flute is a 5-Stage Open Source RISC-V Processor

Bluespec is a US company that provides RISC-V processors and development tools that “speed integration, debugging and verification of embedded systems”. Their first RISC-V release was the Piccolo 3-stage in-order processor targeting low end embedded systems and IoT applications.

The company has now announced Bluespec Flute a 5-stage in-order open source RISC-V processor with the release of a synthesizable Verilog for a bare metal RV32IMA core and a supervisor level RV64IMA core.

Bluespec FluteBluespec Flute key features:

  • RV32IMU with ‘M’ extension (integer multiply/divide)
  • RV64IMASU with ‘A’ extension (atomic memory ops) and ‘M’ extension (integer multiply/divide)
  • AXI4-Lite interface
  • 5-stage pipeline
  • 100 MHz (Xilinx UltraScale)
  • < 5000 LUTs (Xilinx UltraScale)
  • 4KB Instruction & Data caches
  • Hardware multiply-divide
  • RISC-V Debug Module

You’ll find the source code in BSV (Bluespec SystemVerilog) and instructions to get started in Github. Bluespec Flute core has been tested in Xilinx UltraScale/UltraScale+ boards so far. In the future, the company will add floating point and compressed instructions (RV32GC/RV64GC), as well as work on Linux and FreeRTOS support.

At least one company is currently developing a commercial product based on Bluespec Flute: Calligo Technologies, an HPC/AI Company based in Bangalore, India. Anantha Kinnal, Co-founder & Director of  the company, explains: “we are using Bluespec’s Flute core as a fast and efficient way to take to market our Posit Numeric Unit IP”.

Beside the Github repository, more details about Flute RISC-V core can be found on the product page.

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4 years ago

What are the U and S extensions, if they’re extensions, in the first place? The established extensions as of ver 2.2. are MAFDQLCBTPV.

4 years ago

User and Supervisor. They are defined in the privileged ISA spec, not the user-level spec.

4 years ago

Gotcha, thanks.

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