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FPGA-based add-on board brings PCIe to the first Linux-based RISC-V SBC

May 4, 2018 — by Eric Brown 4,471 views

Microsemi announced a “HiFive Unleashed Expansion Board” built on its PolarFire FPGA that adds PCIe and USB expansion for the RISC-V-based, Linux driven HiFive Unleashed SBC.

Microsemi and its board manufacturing partner Pactron have gone to Crowd Supply to launch an FPGA add-on board for SiFive’s RISC-V based HiFive Unleashed SBC. The open-spec HiFive Unleashed Expansion Board adds PCIe root port capability to SiFive’s Linux-driven SBC, letting developers add PCIe cards for graphics, storage, audio, network, keyboard/mouse, and more. USB ports provide further expansion for the USB-deprived HiFive Unleashed, which runs Linux on a RISC-V based Freedom U540 SoC (see farther below).

The PCIe support makes it easier to build a fully configured RISC-V PC, such as a “Linux development workstation,” says Microsemi. It adds: “Port your linux distro to this platform and all of your favorite packages.”

HiFive Unleashed Expansion Board
(click image to enlarge)

The 10.7 x 4.62-inch HiFive Unleashed Expansion Board is available for $1,999 on Crowd Supply with current orders due for delivery on May 30. The first HiFive Unleashed boards ordered on Crowd Supply for $995 were set to ship at the end of March, but the bulk of the orders will ship at the end of June.


HiFive Unleashed

Microsemi has led the way in developing soft-core implementations that can run on FPGAs for prototyping, and it was an early adopter of the open source RISC-V architecture. The company offers a soft-core SmartFusion 2 SoC FPGA for use with developing for SiFive’s MCU-like Freedom E300 SoC, which also drives SiFive’s Arduino compatible HiFive1 development board. There’s also Arduino Cinque board based on the HiFive1, jointly developed by SiFive and Arduino.

With the HiFive Unleashed Expansion Board, Microsemi is for the first time addressing the Linux side of the RISC-V market. The board is driven by its PolarFire FPGA. Microsemi has selected an upper mid-range PolarFire MPF300T part with 300K Logic Elements (LEs), as well as a soft IP block that includes RISC-V support. The FPGA is provided in an FCG1152 package

HiFive Unleashed Expansion Board detail view (left) and PolarFire FPGA block diagram
(click images to enlarge)

The board comes pre-programmed with a chiplink to the PCIe Root Port bridge, and is equipped with a 24 lane PCIe switch, a PCIe x1 slot, and a PCIe x16 slot with 4x PCIe lanes. Onboard RAM is listed as “4 Gbit DDR4 x16,” and you get SPI flash for remote FPGA updates and QSPI flash “connected to GPIO,” says Microsemi.

HiFive Unleashed Expansion Board block diagram
(click image to enlarge)

There are SATA and M.2 SSD connectors, as well as a microSD slot and eMMC expansion. The board is further equipped with 2x USB 2.0 host ports, 2x micro-USB ports, 2x CAN transceivers, and an FMC connector. You also get a FlashPro4 programming dongle, a 12V input with AC power adapter, and a USB cable.

Backers receive a free 1-year Libero Gold License, a “$995 value” that offers access to the PolarFire FPGA’s Libero development platform. “Initially only a fixed bitstream enabling a PCIe Root Complex is supplied with the kit,” says Microsemi. “We plan on opening up the kit for designers in the future. At that time the Libero license can be activated.” Microsemi adds that developers can sign up to be notified of future FPGA bitstream upgrades for the board.

RISC-V and HiFive Unleashed background

It’s been over two years since the open source RISC-V architecture emerged from UC Berkeley and began appearing in soft-core implementations designed for FPGAs, and over a year since the first commercial silicon arrived. So far, the focus has primarily been on MCU-like processors, but last October, leading RISC-V vendor SiFive announced the first Linux-driven RISC-V SoC with its quad-core, 64-bit bit Freedom U540 (AKA U54-MC Coreplex).

HiFive Unleashed (left) and Freedom U540 block diagram
(click images to enlarge)

The 28nm fabricated U540 SoC is not only the first multi-core and Linux-ready RISC-V processor, but the first to provide cache coherence. In addition to the four 1.5GHz U54 RV64GC CPU cores, the SoC includes an E51 RV64IMAC management core. There’s no GPU or VPU, but third parties are encouraged to integrate coprocessors and peripherals with the help of an open source TileLink interface bus.

The $995 HiFive Unleashed board builds on the U540 SoC by adding 8GB of DDR4 RAM, 32MB quad SPI flash, a microSD slot, and a GbE port. An FMC expansion slot is available, which is used to plug in Microsemi’s new Expansion Board. Both boards are available with schematics and layout files.

Further information

The HiFive Unleashed Expansion Board is available for $1,999 on Crowd Supply with free shipping within the U.S. and $40 worldwide. Deliveries start on May 30. More information may be found on the HiFive Unleashed Expansion Board Crowd Supply page and this Microsemi documentation page for the board.

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One response to “FPGA-based add-on board brings PCIe to the first Linux-based RISC-V SBC”

  1. Harry Reed says:

    So much for the hobbyist/maker market. Nice product, but only commercial interests will want to afford it . Sadly.

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