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!.

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

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

• 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

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

• 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

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"'.

Xv6 porting is done in 4 months by

• b-inary (UCC, simulator, assembler), https://github.com/b-inary
• censored (MMU), https://github.com/censored--
• kw_udon (UCC), https://github.com/kw-udon
• MasWag (FPU), https://github.com/maswag
• mh (xv6), https://github.com/m-hys
• nullpo_head (xv6, simulator), https://github.com/nullpo-head
• warelle (xv6, simulator), https://github.com/warelle
• wasabiz (UCC, CPU), https://github.com/wasabiz