Understanding CROCOS source code

This document explains how the CROCOS source code is organised and gives hints to port CROCOS on others architectures.

|
+ doc/
|  + README, phases...          text files documention
|  + html/
|     + index.html...           html files documentation
|
+ disk_img/                     ext2 disk image used for tests
|
+ phase_1/                      code for phase 1
+ phase_2.1/                    code for phase 2.1
+ ...                           ...

The definition for "first phases" can be found in " How to build, test and use CROCOS ": In these phases, user programs and the kernel are linked together and the kernel is run inside a Linux process.

|
+ Makefile, rules.mk, var.mk    main Makefile files
|
+ crocos/                       kernel code
|  + main/
|  |  + main.c                  entry point for the kernel
|  |
|  + devices/                   devices related code (drivers)
|  + fs/                        file system code
|  + intr/                      interrupt handlers
|  + process/                   tasks manager
|  |
|  + include/
|     + config/config.h         system configuration
|     + devices/                include files for device drivers
|     + fs/                     include files for file system
|     + intr/                   include files for interrupt handlers
|     + process/                include files for the tasks manager
|
+ klibc                         klibc code
|  + src/                       source code
|  + include/
|  |  + klibc/                  include files
|  + test/                      test programs for the klic
|  + klibc.a                    klibc library after compilation
|
+ usr/                          user-space related files
   + lib/                       directory for user-space libraries
   |  + libcrocos.a             libcrocos library after compilation
   |                               (defines system calls)
   + src/
   |  + crocos/                 source files for libcrocos library
   |  + init/
   |  |  + init.c               init task code
   |  + test/                   test programs for CROCOS
   |     + fork.c, fork.res     test for fork + expected output
   |     + ...
   |
   + include/
      + crocos/                 include files for user programs
                                    (declare system calls, errno...)

Notes:

•

In "first phases", the device drivers directory contains code to print messages on the terminal (with the Linux write system call), to shuts the system down (with the Linux _exit system call) and to load the disk image file in memory (with the Linux open, read and close system calls).

•

The interrupt handler directory contains the code to manage system calls. Indeed, in later phases, system calls will be implemented with a software interruption.

In the above layouts, arch directories are missing. Those directories contain code related to a specific architecture (one directory per architecture). Such directories can be found, for example, in klibc/include/klibc/arch or crocos/include/process/arch.

Porting CROCOS to a new architecture should only require changes in those arch directories. Basically, all the functions/macros defined in an arch directory need to be rewritten for a specific architecture in a dedicated directory. Note that the var.mk file (in the root directory of a phase) also needs to be updated so that the ARCH variable can be defined to a new architecture (see How to build, test and use CROCOS for more informations on the ARCH variable).