What the hell this thing does?

Well, this is just a project for the Digital Techniques signature at Electronics Engineering in UTN FRBA, Argentina. This program initializes a x86 Intel compatible processor, thanks to Dario Alpern for the code of the initialization, and then runs some API initialization for running a minimalistic kernel with five tasks. Some system calls are implemented, pagination, keyboard handler and other features. I have to thank Diego Garcia for the code of the RTC too.

Enjoy it!

PS: I will translate the comments in code to English for better understanding of people and I will make a wiki for keeping things right.

Tools

This code has been done with:

• Bochs x86 Emulator 2.6.2
• Kate: 3.8.4
• NASM version 2.10.01 compiled on Jun 14 2012
• GNU Make 3.81
• Several cups of coffe
• Time, effort and frustration
• Google!

Contenido de cada archivo:

• memory_map.txt: it has a description of the application memory map.
• init16.asm: it has the real mode initialization.
• init32.asm: it has the protected mode initialization.
• exception.asm: it has some exception handlers and some application code to work with pagination and display some error messages.
• interruption.asm: is has some exception handlers such as keyboard and tick.
• fifo.asm y fifo.inc: a FIFO API.
• keyboard.asm y keyboard.inc: a Keyboard API.
• numeric.asm: some number handler API.
• pagination.asm y pagination.inc: it has code to initialize the pagination structures of the involved tasks.
• sys_tables.asm: it has the GDT and IDT description. It also containes some other descriptors for the application and memory control.
• system.asm: all the Kernel.
• tasks.asm: the tasks code and memory.
• tss.inc: some defines and structure definitions.
• video.asm y video.inc: video memory manager.
• main32.asm: main app code. However it is not used right now.

System Calls

To create a system call follow these steps:

• Write the system call code. Define an ID in the system.inc file and modify the maximum ID define
• Modify the code of the function systemLoadSysCalls in system.asm and add in the correct position the label of the new implementation function.
• Write a wrapper like this:

wrapper:      
    mov     eax, SYSTEM_API_SYSCALL_ID
    int     0x80
    ret

Initial task or Idle task

The idle task loads some kernel configurations and it just does a hlt and jmp $-1 to reduce the CPU power consumption when no other task has to use the processing time slice. It must be set with priority 1.