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

Disclaimer
----------

THIS IS A WORK IN PROGRESS.

This is a simple and useless "operating system", with very basic 
features, sorry. It is the fruit of my fundamental explorations of 
the x86 architectures,  32-bit protected mode, interrupt handling, 
memory management, schedulung the floppy disk controller, networking 
as well as VESA and a couple of other things.

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

Copyright M.Idziorek 2014 <m.i@gmx.at> unless stated otherwise!

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Supported Platforms
-------------------

FoolOS is tested/developed on the following emlators/machines

* bochs 2.6.6 (compiled with: ./configure --enable-clgd54xx --enable-a20-pin --enable-debugger --enable-disasm --enable-e1000 --with-x --with-x11 --enable-smp)
* qemu 1.1.2

* virtual box 4.1.18 (disable nested paging etc)
* my laptop (Acer Aspire 1810TZ)
* my desktop (Q6600 on Asus p5n32-e sli plus)

Features
--------

All features are only very rudiemntary and buggy.

* PIT support / Timing
* PIC support & Interrupt handling framework
* PCI bus scanning
* Physical memory management
* Virtual memory managment (Paging)
* Multitasking (2 tasks so far)
* Floppy disk driver
* VESA 

Todos
-----

Some things I would like to add someday:

* port c lib and gcc
* Filesystem (probably ext2)
* e1000 driver
* drivers to read/write usb sticks 
* networking stack / webserver
* user space / ring3 / ELF binaries support
* mouse support
* simple window manager
* support multiple processors!
* 64-bit support
* alternatively grub as bootloader
* implement a real shell (in user mode)
* kernel should run in high memory (~3gb) virutal mem. why? except v86 tasks?
* let processors sleep if there is no work
* switch from PIC to APIC!
* use ACPI instead of MP spec.
* install idt for second processor!

Issues
------

* memory map and some other locations are hardcoded.
* the first ~4mb of physical mem are reserved by mem manager (hardcoded)
* bootloader loads only 52 sectors of kernel into mem. ~25KB!
* size of bitmap to track free blocks of physical memory is hardcoded to max.
* Assumed suport for Vesa mode 0x114 with linear addressing!
* My Acer Aspire seems to lack MP tables, switch to ACPI
* virtual box enables VT-x for MP, which makes FoolOS hang on VM init.


MEMORY LAYOUT
=============

floppy image
------------
* 0x0000 - MASTER BOOT RECORD
* 0x0200 - kernel image (contains sotrage for interrupt desc. table)
* 0x6400 - fool-font binary
* 0x8000 - file system will go here?

ram
---

0x1000
    boot loader puts the kernel binary here.

0x7000
    entry point for APs (Application Processors).

0x7c00 
    first stage boot loader (loaded by bios) boot/mbr.asm
    includes initial Global Descriptor Table!

0x7c00 + 3 (after jmp boot_16)
    boot loader puts number of boot floppy disk here.

0x7c00 + 0x600
    boot loader puts number of records in memory map in here!

0x7c00 + 0x400 
    the boot loader puts the memory map obtained from the 
    bios here before switching to protected mode.

0x8300
    boot loader puts the vesa modes here!

0x9000
    esp (stack counts down)

0x9000
    physical memory manager bitmap!!!

0xb000 
    memory above this is used for dma (by our floppy.c driver)


REFERENCES
==========

* LINUX KERNEL
* GNU HURD
* MINIX
* FreeBSD etc.
* xv6
* distributed OS?

* e1000 driver

* http://www.brokenthorn.com/Resources/OSDev17.html
* http://www.jamesmolloy.co.uk/tutorial_html/9.-Multitasking.html
* http://pdos.csail.mit.edu/6.828/2011/labs/lab6/
* http://wiki.osdev.org/Virtual_8086_Mode
* http://pdos.csail.mit.edu/6.828/2011/xv6.html
* http://www.nongnu.org/ext2-doc/
* http://www.osdever.net/tutorials/view/multiprocessing-support-for-hobby-oses-explained
* http://wiki.xomb.org/index.php?title=ACPI_Tables
* http://forum.osdev.org/viewtopic.php?f=1&t=10944
* man syscalls (posix syscalls?)


MY NOTES BELOW THIS LINE
========================

Keyboard Driver
---------------

//some thoughts on redesign of the keyboard driver
//use uint8_t for proc_pos and buff_pos and a BUF_SIZE of 256 for auto wrap!?

// kb input ringbuffer
kb_scancode kb_buff[BUF_SIZE];

buff_pos=0;
proc_pos=0;
buffered=0;

void kb_irq()
{
    cli

    //we get one interrupt for EACH scancode!
    kb_scancode val=get_scancode();

    // think about race condition if called while inside kb_proc();
    if(buffered+1<BUF_SIZE)
    {
	kb_buff[buff_pos]=val; 
	buff_pos++;	    
	buffered++;
    }
    else
    {
	//kb ring buffer is full;
    }
    sti

}


void kb_proc()
{
    if(proc_pos!=buff_pos)
    {
	kb_scancode val=kb_buff[proc_pos];

	proc_pos++;
	buffered--;

	stdin(scancode_to_char(val));
	
    }
}

Linux Startup x86
-----------------
~ ontogeny recapitulates phylogeny ~

Some notes on the Linux statup process, or at least how I understand it.

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