Efinix Buckles Down on 64-bit RISC-V Performance for Embedded FPGA Designs

Efinix has expanded its Sapphire RISC-V SoC family with the Sapphire RV64, a configurable 64-bit processor for embedded FPGA designs. The new core brings larger memory support, additional caching and more I/O capability to applications that have outgrown the limits of the company’s 32-bit Sapphire RV32 SoCs.

The Sapphire RV64 keeps the FPGA-based approach of the existing Sapphire family while providing more processing headroom for embedded Linux, edge AI and other larger applications. Designers can configure the processor, memory, peripherals and optional features around the application rather than implementing a fixed processor configuration.

Moving Sapphire From 32 to 64 Bits

The big change with the Sapphire RV64 is the move to a 64-bit RISC-V architecture. Engineers can configure the SoC with one to four processor cores and run them from 20 to 400 MHz, depending on the FPGA and the rest of the design. The processor uses a seven-stage pipeline, with optional features including floating-point support, atomic operations, compressed instructions and several bit-manipulation extensions.

Sapphire RV64 can be implemented across Efinix Titanium, Topaz and supported Trion FPGA families.

There is also quite a bit more memory capability compared with what you would normally expect from a smaller embedded core. The RV64 can be configured with 4 to 512 KB of on-chip RAM, along with L1 instruction and data caches and an optional L2 cache. For a Linux design, an SV39 memory management unit can be added. Branch prediction, physical memory protection and hardware and software prefetching are also available depending on what the application actually needs.

For designs that need more memory off-chip, the RV64 supports DDR3, LPDDR4x and HyperRAM, with capacities ranging from 4 MB to 8 GB. LPDDR4x can run at up to 3,200 Mbps, and the external memory interface can be configured up to 512 bits wide. That becomes useful for embedded Linux and edge AI designs, where a 32-bit processor and smaller memory space can start becoming a limitation. More information can be found in the Sapphire RV64 SoC data sheet.

Configuring the Processor Around the Application

The RV64 also carries forward one of the more useful features of the Sapphire RV32 architecture: custom instructions. Its optional custom instruction interface supports up to 1,024 IDs, allowing software to call hardware implemented in the FPGA fabric. This gives engineers a way to accelerate specific operations without moving the entire workload away from the processor.

Efinix positions its Titanium FPGA platform for applications including machine vision, medical imaging, industrial automation and automotive systems.

Peripheral options include up to 32 GPIOs, five I²C masters, three SPI masters, three UARTs, three user timers and eight user interrupts. The SoC also provides AXI interfaces for connecting user logic, along with a CLINT timer, platform-level interrupt controller and watchdog timer.

FPGA and Development Support

Sapphire RV64 is available across Efinix Titanium and Topaz FPGAs and Trion devices T20 and above, according to the company’s announcement. Feature availability can depend on the target FPGA. For example, use of the DDR controller requires a device with the necessary hardened DDR interface. Board -level Efinix FPGA development platforms include the Titanium Ti375, Topaz Tz170, and Trion T120—all of which support the Sapphire RV64 SoC.

Efinix FPGA development platforms include the Titanium Ti375 (left), Topaz Tz170 (center) and Trion T120 (right), all of which support the Sapphire RV64 SoC.

Engineers configure the RV64 through the Efinity IP Manager, the same approach used with Efinix’s 32-bit Sapphire SoCs. The Efinity Integrated Development Environment handles the RTL-to-bitstream flow, while the Eclipse-based Efinity RISC-V Embedded Software IDE supports software development, debugging and BSP integration. Standard RISC-V debugging is supported along with up to four hardware breakpoints, four performance counters and FPGA co-debug capability.

The Sapphire RV64 gives Efinix users a step up from its 32-bit cores without moving away from the existing Sapphire development approach. With 64-bit processing, larger external memory, Linux support and configurable FPGA acceleration, it fills the higher end of the Sapphire family for embedded designs that need more processing and memory while retaining the flexibility of a soft SoC.

All images used courtesy of Efinix.