Untethered lowRISC release

December 18, 2015

Over the past several months, we’ve been working to provide a standalone or ‘untethered’ SoC. Cores in the original Rocket chip rely on communicating with a companion processor via the host-target interface (HTIF) to access peripherals and I/O. This release removes this requirement, adding an I/O bus and instantiating FPGA peripherals. The accompanying tutorial, written by Wei Song, describes how to build this code release and explains the underlying structural changes. We support both the Xilinx KC705 and the lower-priced Nexys4 DDR development boards. We would gladly welcome assistance in supporting other boards.

Please note that the codebase temporarily lacks support for tagged memory included in the previous release. We plan to re-integrate tagged memory support with additional optimisations early next year. You can find a detailed list of changes in the release notes. One highlight is support for RTL simulation using the open-source Verilator tool.

This development milestone should make it easier for others to contribute. If you’re looking to get stuck in, you might want to consider looking at tasks such as:

Cleaning up the RISC-V Linux port, improving devicetree support and removing the host-target interface.

Replacing use of proprietary peripheral IP with open-source IP cores.

Adding support for different FPGA development boards, including Altera boards.

Implementing the BERI Programmable Interrupt Controller (p73), and adding necessary Linux support.

Our next development priorities are the re-integration of tagged memory support and an initial integration of a minion core design. We also expect to put out a job advert in the next few weeks for a new member of the lowRISC development team at the University of Cambridge Computer Laboratory. Interested applicants are encouraged to make informal enquiries about the post to Rob Mullins Robert.Mullins@cl.cam.ac.uk.

We hope to see many of you at the 3rd RISC-V Workshop in January, where Wei Song and Alex Bradbury will be presenting about lowRISC.