RVComp

Document

If you want to read the document, please visit the RVComp Documentation Pages.

Demo is here.

Overview

RVComp is a RISC-V SoC (System-on-Chip) featuring a five-stage pipeline. It supports the RV32IMA_Zicntr_Zicsr_Zifencei instruction set, along with M-, S-, and U-modes, the privileged architecture, and the Sv32 virtual memory system, enabling it to run Linux. The RVComp project began in June 2024 and offers the following characteristics:

• High operating frequency: Achieves a maximum clock frequency of 170 MHz (Version 1.0.0) on a Nexys A7-100T (XC7A100T-1CSG324C)
• HDL implementation: RVComp is described in Verilog HDL with a from-scratch design except for the DRAM controller and clock generation
• Permissive licensing: All HDL components except IP are provided under the MIT license
• Ethernet support: 100 Mbps Ethernet controller with RMII (Nexys 4 DDR) and MII (Arty A7) interfaces, including hardware MAC filtering and FCS computation
• microSD boot support: microSD controller enabling Linux to boot and operate from a microSD card on the Nexys 4 DDR board
• Interactive configuration: Various SoC parameters can be configured through a terminal-based GUI (tools/setting.py)
• Docker support: Containerized build environment with simulation tools pre-installed (Vivado must be installed natively)

LICENSE

RVComp files we developed from scratch are distributed under the MIT license.

However, please note that the RVComp project uses multiple open-source components. The following components follow their respective licenses; see the LICENSE file for full details.

• DRAM controller: Xilinx MIG (Xilinx End User License Agreement)

• Clock generation: Xilinx Clocking Wizard (Xilinx End User License Agreement)

• prog/coremark: CoreMark (COREMARK® ACCEPTABLE USE AGREEMENT + Apache License 2.0)

• prog/embench: Embench-IoT (GPL-3.0 License)

• prog/riscv-tests: riscv-tests (The Regents of the University of California (Regents))

• OpenSBI: OpenSBI customized for RVComp (BSD-2-Clause License)

• buildroot: Device drivers, configuration files, and patches to build Linux (GPL-2.0 License).

• RVComp-buildenv: Build scripts that use Buildroot to produce Linux images (GPL-2.0 License). Prebuilt Linux images also include third-party software such as Linux and OpenSBI, so redistribution must follow the licenses of those components.

• tools/XilinxBoardStore: Xilinx Board Store (Apache License 2.0)

Supported instruction sets

• Base ISA: RV32I (integer)
• Extensions:
  • M extension: multiplication and division instructions
  • A extension: atomic instructions (LR/SC and AMO)
  • Zicntr: counter access instructions
  • Zicsr: CSR access instructions
  • Zifencei: instruction-fetch fences
• Virtual memory: Sv32 (two-level page tables with 4 KB pages)

Quick Start

This section explains how to run RVComp on an FPGA board using a prebuilt bitstream and Linux image.

Please download the following files from the release page.

UART boot (Arty A7 35T or Nexys 4 DDR):

• uart_fw_payload.bin: Linux image file for UART boot
• uart_arty_a7.bit: Bitstream for Arty A7 35T (UART boot)
• uart_nexys4ddr.bit: Bitstream for Nexys 4 DDR (UART boot)

MMC boot (Nexys 4 DDR only):

• mmc_fw_payload.bin: Linux image for MMC boot
• mmc_nexys4ddr.bit: Bitstream for Nexys 4 DDR (MMC boot)

MMC boot requires a microSD card inserted into the Nexys 4 DDR board's microSD slot.
If an Ethernet cable is connected to the board, the network interface is available after boot.

Common:

• tools.zip: Programs to communicate with the FPGA board via UART

Please unzip tools.zip.

Please make sure the necessary tools and the FPGA board are ready:

• {ref}Vivado (2024.1 recommended) <vivado>
• {ref}uv <uv>
• FPGA board (Nexys 4 DDR or Arty A7 35T)

UART Boot (Arty A7 35T or Nexys 4 DDR)

1. Please connect the FPGA board to your PC.
2. Please download and extract uart_fw_payload.bin, uart_arty_a7.bit (for Arty A7 35T) or uart_nexys4ddr.bit (for Nexys 4 DDR), and the tools directory from the archive mentioned above, and place them in the same directory.
3. Please determine which serial port the USB connection is using. See Checking the Serial Port below.
4. Please open PowerShell (Windows) or a terminal (Linux) and change to the directory from step 2.
5. Please run the following command, replacing <port> with the value from step 3. On success you should see Port <port> opened successfully..
   • Nexys 4 DDR: cd tools && uv run term <port> 3000000 --linux-boot --linux-file-path ../uart_fw_payload.bin
   • Arty A7 35T: cd tools && uv run term <port> 3000000 --linux-boot --linux-file-path ../uart_fw_payload.bin
6. Please launch Vivado and select Open Hardware Manager → Open Target → Auto Connect → Program Device.
7. When prompted for the bitstream, please choose uart_arty_a7.bit if you use Arty A7, or uart_nexys4ddr.bit if you use Nexys 4 DDR, then click Program.
8. The Linux image is transferred to the FPGA and boot begins. Once the login prompt appears, please log in as root (no password).
9. To use Ethernet, configure the network interface:

   $ ip addr add <IP_ADDRESS>/<PREFIX_LEN> dev eth0
   $ ip link set eth0 up

10. Please press Ctrl+C, then type :q to exit the serial console.

MMC Boot (Nexys 4 DDR only)

MMC boot on Nexys 4 DDR requires a microSD card. The mmc_fw_payload.bin file is a combined binary containing the Linux image and root filesystem; it is written to the beginning of the microSD card. The serial terminal is still used as a console, but it does not send the Linux image in this mode.

Writing the microSD card

Insert a microSD card into your host machine.

Linux:

Identify the block device node with lsblk or dmesg. Verify the device node carefully before proceeding; writing to the wrong device will permanently destroy data on that device.

$ sudo dd if=mmc_fw_payload.bin of=/dev/sdX bs=1M conv=fsync,notrunc status=progress

Replace /dev/sdX with the actual device node of your microSD card (for example /dev/sdb). After the command completes, safely eject the card.

Windows (WSL):

Attach the microSD card to WSL, then use the same dd command as Linux above.

• USB microSD card reader: follow this guide (usbipd) to bind the device to WSL.
• Built-in card reader: follow this guide (WSL2 disk mounting) to mount the disk in WSL.

Booting from microSD card

1. Insert the written microSD card into the microSD slot on the Nexys 4 DDR board.
2. Connect the board to your PC via USB.
3. Determine the serial port as described in Checking the Serial Port.
4. Open a terminal and run the following command. No --linux-boot flag is needed because the serial tool is used only as a console in this mode:

   $ cd tools && uv run term <port> 3000000

5. Launch Vivado and program the board with mmc_nexys4ddr.bit using Open Hardware Manager → Open Target → Auto Connect → Program Device.
6. The bootrom copies the Linux image from the microSD card into DRAM and boots Linux. The root filesystem on the microSD card is mounted as /dev/mmcblk0. Once the login prompt appears, log in as root (no password).
7. To use Ethernet, configure the network interface:

   $ ip addr add <IP_ADDRESS>/<PREFIX_LEN> dev eth0
   $ ip link set eth0 up

8. Press Ctrl+C, then type :q to exit the serial console.

(checking-the-serial-port)=

Checking the Serial Port

Windows

Please run the following command in PowerShell:

Get-CimInstance Win32_PnPEntity | Where-Object { $_.Caption -match 'COM' } | Select-Object Caption, DeviceID

Please identify the entry whose DeviceID contains FTDI; this corresponds to the FPGA board. It appears in the form USB Serial Device (COM*). Please note the COM port name.

WSL

Please follow the instructions in this article to attach USB devices to WSL. Please run usbipd list; the entry with VID:PID of 0403:6010 is usually the FPGA board. After attaching it, please follow the Linux instructions below.

Linux

Please run the following command in a terminal:

$ ls /dev/ttyUSB*

The available USB serial ports are listed. If only one FPGA board is connected as a USB serial device, it is typically /dev/ttyUSB1. When multiple USB serial devices are present, please run the command below for each port and look for a device where ID_VENDOR is Digilent:

$ udevadm info /dev/ttyUSB1 | grep ID_VENDOR=

Please record the /dev/ttyUSB* path assigned to the FPGA board.

Project Information

This project started June, 2024. Project Name: RVComp
Version: 1.1.1
Last Updated: 2026/05/01

Contributors

Contributors to this project are as follows:
shmrnrk
yuyu5510
Kise K.

We would like to appreciate the contributions from shmknrk for his significant contributions to this repository.

Change History

• 2025-10-31: v1.0.0 - Initial release
• 2026-03-30: v1.1.0 - Added Ethernet MAC Controller (RMII/MII), microSD root filesystem support, and various usability improvements.
• 2026-05-01: v1.1.1 - Added Test Script for Spike Comparison and Updated Documentation.