Forked for my Operating Systems Intensive class.  
In the `master` branch, I implemented the unix utilities find and xargs.
I also implemented my own Unix shell,
capable of handling pipes and I/O redirection.
In the `syscall` branch,
I first implemented user-level threads in C and RISC-V.
Then, I modified the kernel to include and accommodate a syscall
that calls a specified function repeatedly at a specified interval.

---- Original README -------------------------------------------------

xv6 is a re-implementation of Dennis Ritchie's and Ken Thompson's Unix
Version 6 (v6).  xv6 loosely follows the structure and style of v6,
but is implemented for a modern RISC-V multiprocessor using ANSI C.

ACKNOWLEDGMENTS

xv6 is inspired by John Lions's Commentary on UNIX 6th Edition (Peer
to Peer Communications; ISBN: 1-57398-013-7; 1st edition (June 14,
2000)). See also https://pdos.csail.mit.edu/6.828/, which
provides pointers to on-line resources for v6.

The following people have made contributions: Russ Cox (context switching,
locking), Cliff Frey (MP), Xiao Yu (MP), Nickolai Zeldovich, and Austin
Clements.

We are also grateful for the bug reports and patches contributed by
Silas Boyd-Wickizer, Anton Burtsev, Dan Cross, Cody Cutler, Mike CAT,
Tej Chajed, eyalz800, Nelson Elhage, Saar Ettinger, Alice Ferrazzi,
Nathaniel Filardo, Peter Froehlich, Yakir Goaron,Shivam Handa, Bryan
Henry, Jim Huang, Alexander Kapshuk, Anders Kaseorg, kehao95, Wolfgang
Keller, Eddie Kohler, Austin Liew, Imbar Marinescu, Yandong Mao, Matan
Shabtay, Hitoshi Mitake, Carmi Merimovich, Mark Morrissey, mtasm, Joel
Nider, Greg Price, Ayan Shafqat, Eldar Sehayek, Yongming Shen, Cam
Tenny, tyfkda, Rafael Ubal, Warren Toomey, Stephen Tu, Pablo Ventura,
Xi Wang, Keiichi Watanabe, Nicolas Wolovick, wxdao, Grant Wu, Jindong
Zhang, Icenowy Zheng, and Zou Chang Wei.

The code in the files that constitute xv6 is
Copyright 2006-2019 Frans Kaashoek, Robert Morris, and Russ Cox.

ERROR REPORTS

Please send errors and suggestions to Frans Kaashoek and Robert Morris
(kaashoek,[email protected]). The main purpose of xv6 is as a teaching
operating system for MIT's 6.828, so we are more interested in
simplifications and clarifications than new features.

BUILDING AND RUNNING XV6

You will need a RISC-V "newlib" tool chain from
https://github.com/riscv/riscv-gnu-toolchain, and qemu compiled for
riscv64-softmmu. Once they are installed, and in your shell
search path, you can run "make qemu".