* vi: ft=markdown

Welcome to FoolOS
=================

Copyright M.Idziorek 2014 <m.i@gmx.at>

Disclaimer
----------

This is a simple and useless "operating system", with very basic 
features, sorry. It is the fruit of my fundamental explorations of 
the 32-bit protected mode, interrupt handling, memory management and 
some other things.

![Screenshot of FoolOS](/screenshots/foolos.png?raw=true "FoolOs Kernel")


NOTES
=====

cli; disable interrupts
lgdt
lidt
sti; enable interrupts

Linux Startup x86
=================

1. arch/x86/boot/header.S

Contains the header and linux 16 bit code.

This code should be entered with a bootloader at the address specified 
within the header (as _start) which will put us at 'start_of_setup'

Direct loading will put us at 'start2' at the very start which will
show an error message

If everyhing goes right we will enter the 16-bit real mode C module 
with:

call main ; should not return

2. arch/x86/boot/main.c

void main(void) will do some checks and detections (cpu,mem,..) and
invoke: go_to_protected_mode();

3. arch/x86/boot/pm.c

go_to_protected_mode() - will disable interrupts and set up the initial 
idt and gdt descriptor tables before calling: protected_mode_jump() and 
passing the address of code32_start.

4. arch/x86/boot/pmjump.S

back in assembly-world the actual transition is made inside 
'protected_mode_jump' and we move on to 'in_pm32' where the data segment
is set up and we jmpl to the 32-bit entry point of the kernel.

5. arch/x86/kernel/head32.c (assumption!?)

void i386_start_kernel(void)

6. init/main.c

start_kernel(void)

setup_arch()!!

Interrupts
==========

arch/x86/include/asm/irq_vectors.h each entry is 8 bytes

ISA interrupts:

0x30 0x0000 0x0000 0x0000 0x0000
0x31
0x32
..
0x3f


TODOS
=====
    * study LINUX KERNEL
    * GNU HURD
    * MINIX
    * FreeBSD etc.

NETWORK
=======

    look at following linux drivers:
    * e1000

notes
=====

* posix - minimal set of function calls! 
* distributed os
* caches L1,L2,L3
* controller -> ide inteface of device
* probe memory!
* a20~ wrap

* ssd card reader
* cobol fortran algol? compilers? 

* quotation: ontogeny nrecapitulates phylogeny

* own simple sell

check:
apertium?
clang 
freebsd 
user-mode-linux

REFERENCES
==========

http://www.brokenthorn.com/Resources/OSDev17.html