OS/161 is a teaching operating system, that is, a simplified system used for teaching undergraduate operating systems classes. It is BSD-like in feel and has more "reality" than most other teaching OSes; while it runs on a simulator it has the structure and design of a larger system.

More info here: http://os161.eecs.harvard.edu

1. Create a file in kern/main/yourfile.c and write a function

2. Modify kern/main/main.c entering a call to your function

3. In test.h:

   #include "opt-yourfile.h" //(opt-optname.h)
   Insert a prototype of your function  
   

4. Modify kern/conf/conf.kern inserting the new file (#Startup and initialization):

    defoption yourfile
    optfile   yourfile   main/yourfile.c
   

5. Generate in kern/conf a new file (for example YOURFILE)

    It can be a copy of DUMBVM adding a new line: "options yourfile"
   

6. Finally do the make of the kernel:

      In kern/conf
          ./config YOURFILE
          
      In kern/compile/YOURFILE
          bmake depend
          bmake
          bmake install
   

1. In kern/arch/mips/syscall/syscall.c there is switch case in which you can menage the system calls

2. To menage a system call it's necessary an integer code. See:

   kern/include/kern/syscall.h
   

3. Create your system call in kern/syscall/my_syscalls.c

4. Modify kern/include/syscall.h adding a prototype of the syscall function

5. Modify kern/conf/conf.kern inserting the new file (#System call layer):

   file syscall/my_syscalls.c
   

6. Finally do the make of the kernel

    In kern/conf
      ./config DUMBVM
      
    In kern/compile/DUMBVM
        bmake depend
        bmake
        bmake install