A minimal operating system on a small RISC-V board

With only 2000 lines of code, egos-2000 implements boot loader, microSD driver, tty driver, memory paging, address translation, interrupt handling, process scheduling and messaging, system call, file system, shell, 7 user commands and the mkfs/mkrom tools. It runs on a $129 small development board.

# Count lines of code excluding references and README.md
> cloc egos-2000 --exclude-ext=md,pdf
      62 text files.
      61 unique files.
      13 files ignored.

github.com/AlDanial/cloc v 1.92  T=0.03 s (1668.0 files/s, 105414.7 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                               35            454            490           1565
C/C++ Header                    11             74            105            313
Assembly                         3              6             24             68
make                             1             11              0             54
-------------------------------------------------------------------------------
SUM:                            50            545            619           2000 << exactly 2000!
-------------------------------------------------------------------------------

Earth and Grass Operating System 2000

egos and egos-2000 are the teaching operating systems we use at Cornell. They have the same architecture.

• The earth layer implements hardware-specific abstractions.
  • tty and disk device interfaces
  • cpu interrupt and memory management interfaces
• The grass layer implements hardware-independent abstractions.
  • processes, system calls and inter-process communication
• The application layer implements file system, shell and user commands.

The definitions of struct earth and struct grass in egos.h specify the interfaces between these layers.

Hardware Requirements

• an Artix-7 35T Arty FPGA development board
• a microUSB cable (e.g., microUSB-to-USB or microUSB-to-USB-C)
• [optional] a microSD Pmod, a microSD reader and a microSD card (e.g., Sandisk, Samsung or PNY)

Software Requirements

• To compile egos-2000: SiFive freedom riscv-gcc compiler
• To program the on-board ROM: OpenOCD for Linux/MacOS or Vivado for Windows
• To connect with the serial tty: screen for Linux/MacOS or PuTTY for Windows
• [optional] To program a disk image file to the microSD card: dd or balena Etcher

Usages and Documentation

For compiling and running egos-2000, please watch the tutorial video and read USAGES.md. This document further introduces the teaching plans, architecture and development history of egos-2000.

The RISC-V instruction set manual introduces the privileged registers used by egos-2000. The SiFive FE310 manual introduces the processor used by egos-2000, especially the GPIO, UART and SPI bus controllers.

For any questions, please contact Yunhao Zhang.

Acknowledgements

Many thanks to Robbert van Renesse and Lorenzo Alvisi for their support. Many thanks to Meta for supporting me with a fellowship. Many thanks to all CS4411 students at Cornell over the years for helping improve this course.