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xv6 GAIA port

xv6 port

This is a port of xv6 to GAIA, our own CPU architecture.
We did this at the student experiment at The University of Tokyo.
Rewriting xv6 is mainly done by @nullpo-head, @warelle and @m-hys.
Many improvements are also done by other team members.

To make xv6 work on GAIA, we did

  • Rewrite all x86 dependent codes such as booting, interrupt, peripherals or task switch.
    This was indeed heavy, but not as heavy as expected at first.
  • Support page coloring.
    To handle the cache coherency problem GAIA has at present.

About 1000 lines modifications are needed for these tasks.
For diff, see https://github.com/wasabiz/xv6/compare/6f8ad7a249fc9b47a449f0f35ec79aa0b01b0069...master

There is an experimental online demo of xv6-gaia by Javascript. Try it!.

Original xv6

The original xv6 is a simple Unix like OS for education by MIT, which is targeted at x86.
For more detail, see http://pdos.csail.mit.edu/6.828/2012/v6.html

What we did for porting

Porting needs much more than just rewriting xv6. Here is what we did for porting.

Create toolchain

  • Create the almost C89 compatible compiler
    Maybe this is the biggest task. We made an almost C89 compatible compiler, UCC.
    This is done by @kw-udon, @b-inary and @wasabiz.
    The repository is at https://github.com/kw-udon/ucc/.
  • Create the assembler
    We made a simple but powerful assembler by python. This is done by @b-inary.
    Repository: https://github.com/b-inary/gaia-software
  • Create the linker
    The linking is done by some ruby scripts and makefile. This is done by @nullpo-head

Create CPU simulator

A software CPU simulator is necessary to develop CPU.
@b-inary mainly made this.

Create CPU

  • Design CPU architecture
    @b-inary and @wasabiz designed GAIA architecture.
    @nullpo-head also joined for interruption and MMU.
  • Create CPU by VHDL
    GAIA is implemented on FPGA, Virtex-5.
    @wasabiz wrote all VHDL source by hisself.
    The repositroy is at https://github.com/wasabiz/gaia3

Improvements

We also did some improvements.

  • Add user programs
    pwd, tiny vi clone, sl, 2048 and many user programs are added.
    Try sl at least once!!
  • Clean up the source codes
    We separated kernel and user programs into different directories.
    We also introduced a subset of standard libc. You can include '<stdio.h>', instead of '"user.h"'.

Team members

Xv6 porting is done in 4 months by