HiFive Unmatched SBC showcases new FU740 RISC-V SoC

HiFive Unmatched SBC showcases new FU740 RISC-V SoC

Oct 30, 2020 — by Eric Brown

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SiFive has opened $665 pre-orders on a “HiFive Unmatched” Mini-ITX dev board that can power a PC. The SBC runs Linux on a penta-core, 64-bit SiFive FU740 SoC and offers 2x M.2 and PCIe x16 for graphics.

In September when SiFive announced its FU740 (Freedom U740) SoC, the RISC-V chip designer said it would soon demo the SoC running a PC. At the time, we speculated that the demo would include a new HiFive dev board to update the Linux- and U540-driven, $999 HiFive Unleashed, which runs on the earlier Freedom U540 (FU540). Indeed, SiFive has now opened pre-orders on a $665 HiFive Unmatched Mini-ITX board due in the fourth quarter that runs Linux on a U74-MC.

HiFive Unmatched
(click images to enlarge)

Demonstrated at the Linley Fall Processor Conference, the HiFive Unmatched is billed as the “world’s fastest native RISC-V development platform.” The Unmatched is primarily designed to power PCs. Yet, with a processor that may well be slower than the quad- A72 Broadcom SoC on the Raspberry Pi 4, SiFive’s potential PC customers are likely eyeing the low-end Linux laptop niche currently led by Google’s ChromeOS. We imagine the Unmatched will also inspire some embedded designs.

Based on SiFive’s 64-bit, Linux-capable U7-series of Cortex-A55 like cores, the FU740 is claimed to deliver 2.5 DMIPS/MHz and 4.9 CoreMark/MHz performance. The U7-series includes a single-core U74 and a quad-core U74-MC used on the Unmatched board. The MC model adds a fifth real-time monitor core based on its similarly, 64-bit Core IP 7 Series architecture S7 MCU core.

FU740 block diagram (left) and mix+match conceptual diagram
(click images to enlarge)

In July, SiFive upgraded its U7- and earlier U5-series CPUs with a “20G1” release that boosted performance and reduced power. Earlier this month it released an additional 20G1 6.0 update for the U7. All these processors use the royalty-free RISC-V architecture.

The U7 series offers a “mix+match” heterogeneous multi-core technology much like Arm’s Big.Little with DynamIQ. Mix+match enables the addition of the FU740’s fifth monitor core but it could also be used in other multi-core configurations with lower-power E7 cores. SiFive originally announced mix+match as part of it Cortex-A72 like, 7nm capable U8-Series, which may use it in octa-core configurations with cores running at different speeds. For more details on the U7, see our FU740 report.

HiFive Unmatched detail view and block diagram
(click images to enlarge)

Despite offering far more features than the HiFive Unleashed, the larger HiFive Unmatched costs about a third less. Like the Unleashed, the HiFive Unmatched is an open spec board with schematics. It similarly ships with 8GB DDR4, 32MB quad SPI flash, and a microSD slot.

A 32GB microSD card is preloaded with the Yocto and OpenEmbedded (OE) Linux based Freedom U-SDK, which appears to be an updated version of the SDK used on the Unleashed. Debian and Fedora should also work.

Although the FU740 is a headless SoC without a GPU, you can add a graphics card via the PCIe x16 slot driven by the SoC’s PCIe Gen3 x8 interface. There are also M.2 M-key and E-key slots for optional NVMe and WiFi/BT cards, respectively.

The 170 x 170mm HiFive Unmatched board provides a GbE port, 4x USB 3.2 Gen1 (USB 3.0) ports, and a micro-USB serial console port. Other features include 24-pin GPIO, JTAG, and an RTC. An ATX power supply is also available. It’s unclear whether the small fan and heatsink shown in the image farther above are optional.

Specifications listed for the HiFive Unmatched include:

• Processor — SiFive U74-MC (64-bit RISC-V FU740) with 4x U74 CPU cores @ 1.4GHz (can clock to 1.5GHz) and 1x low-power S7 monitor core; 2MB L2 cache
• Memory /storage:
  • 8GB DDR4-2400
  • 32MB QSPI NOR flash
  • MicroSD slot with 32GB card preloaded with Freedom U-SDK
  • SSD/NVMe available via M.2 M-key (see farther below)
• Networking:
  • Gigabit Ethernet port with 3M CAT5e cable
  • WiFi/BT available via M.2 E-key (see below)
• Other I/O:
  • 4x USB 3.2 Gen1 host ports
  • Micro-USB UART console port
  • JTAG header
  • 24-pin peripheral I/O (4x GPIO, 2x I2C, 2x QSPI, 2x UART, PWM)
  • Mini-ITX case front panel connector
• Expansion (via PCIe Gen 3 x8):
  • M.2 M-key with PCIe Gen 3 x4 and SSD and NVMe 2280 support (3.9 GB/s data throughput)
  • M.2 E-key (PCIe Gen 3 x1) for WiFi/BT
  • PCIe x16 connector
• Other features — RTC with battery; rear I/O shield; M.2 and ATX case mounting screws/standoffs
• Power — 24-pin ATX connector for 150W ATX supply (sold separately); PMIC; current monitor; FU740 reset; global reset; on/off switch
• Dimensions — 170 x 170mm (Mini-ITX form factor)
• Operating system — Freedom U-SDK with Linux kernel, Yocto; U-Boot, OpenSBI, GCC and LLVM toolchains, performance tools and utilities; supports Fedora and Debian; bare metal support via Freedom E-SDK

Further information

The HiFive Unmatched is available for $665 pre-order, with shipments due in Q4 2020. More information may be found in SiFive’s announcement and product page, which has a pre-order button that says “contact sales.” The Freedom U-SDK may be found on this GitHub page.