SiFive HiFive Unmatched

You expect shipped hardware to match its spec sheet, or to quietly fall a little short of it. The HiFive Unmatched went the other way. SiFive announced it in October 2020 with 8 GB of DDR4 and then, six weeks into the Crowd Supply campaign, doubled that to 16 GB for every kit without touching the price.

The memory on this board is soldered down and cannot be added to later, so that extra 8 GB was not a bonus you could have arranged for yourself. It was the difference between a machine that can compile its own software in comfort and one that swaps while trying. In late 2020 the whole point of owning RISC-V silicon rather than running it under QEMU was to do the memory-hungry work — kernels, toolchains — natively, and native builds are exactly where the headroom earns its keep.

The board was also the first serious attempt to stand a RISC-V machine on a desk in an ordinary Mini-ITX case rather than hang a bare dev board off a lab bench. SiFive priced it at $665, built it around the Freedom U740 — four U74 application cores and one S7 monitor core — and sold it through Crowd Supply, where it funded in weeks: $321,091 from 384 backers by 15 December 2020. First boards shipped in May 2021. Then the story bends the way a lot of 2021 hardware did. On 19 January 2022, SiFive’s Phil Dworsky posted to the company forum that, with supply-chain problems it had already fought through once and was still facing, it would not build another run of the Unmatched and would put its effort into the next generation instead. The board was discontinued about eight months after it started shipping.

It came back quietly. In November 2023 SiFive released the HiFive Unmatched Rev B — same FU740, with the power handling reworked so the board starts on its own when mains power returns and can be shut down from software, the things you need when a machine lives in a cluster and nobody is standing at it. Rev B is what SiFive sells today. The original is filed on the vendor’s own site under Legacy Boards, and the lifecycle: discontinued above belongs to that original board, not to the line as a whole.

What I want from it is straightforward. RISC-V is one of the architectures the release engineering platform has to target, and for a long time the honest way to build for it was to cross-compile or emulate. A native build node closes that gap: a machine that runs the toolchain on its own instruction set, so what comes out has been through a real RISC-V userland instead of QEMU’s approximation of one. That is the job I have in mind for this board.

It came through Crowd Supply, which is where both the original board and the Rev B were sold, so the channel alone does not say which of the two sits in the lab. That still turns on the board itself — an original 2021 unit or a Rev B — and it changes small things: the power-on behaviour, and where on the wide spread of quoted prices my own receipt would land. The generation, what I have actually run on it, and a photo are all still to be documented.

Sources: SiFive’s own HiFive Unmatched datasheet, software reference manual, Freedom U740-C000 manual, schematics, bill of materials, and getting started guide; the SiFive product page and the 2022 discontinuation forum post; the Crowd Supply campaign and its update history; and independent coverage from CNX Software, LinuxGizmos, Phoronix, and HotHardware. The specifications, with the figures that disagree across sources, are on the specifications page.