Last updated on March 9, 2021
Sifive has presented the Hifive Unmatched, a circuit board in mini-ITX format with a RISC-V processor . The board uses a Freedom U740, this chip combines five CPU cores with various I / O functions and is suitable for various Linux distributions.
The basis of the Freedom U740 manufactured in 28 nm by TSMC is the U74-MC , i.e. four U7 and one S7 cores. This is a 64-bit design that integrates various RISC-V extensions: The U7 cores are designed as RV64GC, i.e. with support for the general purpose and the compressed extension. The little S7 is an RV64IMAC without additional floating point support.
A core complex alone does not make a system-on-a-chip, which is why Sifive has expanded it to include I / O functions: The Freedom U740 supports DDR4-3200 memory and is the first RISC-V SoC to have eight PCIe Gen3 lanes, the board is equipped with 8 GByte DDR4 and native Gigabit Ethernet (RJ-45) via GMI.
HiFive Unmatched (Image: SiFive)
The eight lanes are attached to an Asmedia switch: there is an x8 slot for a graphics card, an M.2 x4 slot for an SSD, another M.2 x1 slot for a Bluetooth / WiFi module and four USB-A-3.2-Gen1 ports. The Hifive Unmatched’s predecessor, the Hifive Unlimited with Freedom U540, was still missing I / O functions such as USB. An extension board with a Polarfire FPGA was therefore necessary.
There is also a slot for a micro SD card, which is why the Hifive Unmatched is delivered with a 32 GB memory card. A Linux distribution including an Xfce4 desktop is preinstalled there; In principle, Sifive has worked with the Debian Project and Fedora Project, own images can be implemented using the Freedom-U-SDK .
The system is put into operation via a 24-pin ATX power connection, so it behaves like a classic desktop circuit board. In general, the board is intended for developers who want to work with compilers, libraries and applications for RISC-V. Sifive is selling the HiFive Unmatched for $ 665 before tax starting in the fourth quarter of 2020.