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SiFive RISC-V Rack Cluster and custom PC power up with HiFive Unmatched

Dec 9, 2021 — by Eric Brown 1,604 views

SiFive and AB Open demoed a “SiFive RISC-V Rack Cluster” that runs Linux on four of SiFive’s RISC-V U74 based HiFive Unmatched boards. AB Open and Future Computing recently announced a PC design based on the SBC.

At the RISC-V Summit in San Francisco this week, RISC-V chipmaker and designer SiFive demonstrated a SiFive RISC-V Rack Cluster with 4x HiFive Unmatched SBCs. The four-way, rackmount cluster collaboration with AB Open appears to be the first cluster kit using RISC-V technology. Last month, AB Open joined with Future Computing to unveil a custom desktop PC based on the Unmatched and has posted some open source hardware and software files for the project (see farther below).

SiFive RISC-V Rack Cluster
(click images to enlarge)

We found out about SiFive’s rackmount cluster demo from Tom’s Hardware, which calls it an HPC cluster kit. This appears to be a proof-of-concept and perhaps a prototype for a future product. Although AB Open provides a thorough overview and a short video about the design, we did not see any detailed specs or schematics.

One of the key components developed by AB Open is a control board, which is built around SiFive’s original development kit: the Arduino compatible HiFive1 board. The HiFive1 is based on one of SiFive’s first RISC-V architecture MCUs, the FE310.


HiFive Unmatched

The HiFive Unmatched Mini-ITX board runs Linux on SiFive’s FU740 SoC, which is equipped with four of SiFive’s Cortex-A55 like U74-MC cores. The U74-MC is now part of what SiFive calls the Essential 7-series. There is also a fifth core, a real-time, 64-bit monitor core based on the Essential 7-series S7 MCU core.

The HiFive Unmatched ships with 16GB DDR4 (upgraded a year ago from the original 8GB), as well as 32MB QSPI and a microSD slot. Other major features include GbE, 4x USB 3.2 Gen1, and a micro-USB serial console port. The SBC also supplies 24-pin GPIO, JTAG, an RTC, and a PCIe x16 slot driven by the SoC’s PCIe Gen3 x8 interface. (For more on the Unmatched, see this recent Hot Hardware review.)

On the cluster kit, the quartet of Unmatched boards are fixed to a thick aluminum mounting plate. The side panels are loaded up with “high quality” ebm-papst fans.

A PicoPSU with ATX power rail is fitted to each Unmatched board. An INA260 precision digital current and power monitor is attached to each of the SBC’s 12VDC supplies. The HiFive1-based control board is equipped with 4x relays for hard power control and MOSFETs for toggling the Unmatched SBCs’ power and reset lines.

SiFive RISC-V Rack Cluster control board with HiFive1 (left) and Rear Panel
(click images to enlarge)

The cluster kit provides a Rear Panel board that provides “feed-through” for the GbE ports, 4x micro-USB serial console ports, and a separate micro-USB port that links to the control board. The Rear Panel is fitted with a power button and an OLED display divided into four squares for indicating full power (filled square), power only to PicoPSU (half-filled square) and no power (empty).

Custom RISC-V PC

On Nov. 30, AB Open and Future Corporation of Japan announced they had developed a personal computer based on the HiFive Unmatched. The project follows an earlier AB Open project in 2019 to develop one of the first RISC-V based PCs. The system was built around SiFive’s earlier, FU540 powered HiFive Unleashed SBC.

Custom RISC-V PC
(click image to enlarge)

The new PC based on the Unleashed includes an Unmatched board with 16GB RAM. There is also a dedicated Nvidia GeForce GT710 graphics card, 1GB of NVMe storage, and a WiFi radio.

The custom chassis integrates a “smart” front panel with OLED display that communicates with the SBC via a custom Python application. The I2C connected display provides “at-a-glance monitoring of system statistics including CPU and memory usage, component temperatures, and more,” says AB Open. The panel also provides power and reset buttons and dual GPIO-linked user buttons, which default to pagination keys.

ABOpen set up a GitHub page for the project that includes the source files for the Linux stack it developed for the system. AB Open and Future Corp. also posted KiCAD files and source code for the custom OLED front panel display under a permissive license.

Further information

More information on the SiFive RISC-V Rack Cluster kit proof-of-concept may be found in this AB Open cluster blog post. More on the Future/AB Open Custom RISC-V PC may be found on this AB Open custom PC blog post and GitHub page.

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