Instruction

Build with make

Run with make test

Debug with qemu-system-x86_64 -boot a -fda mbr -s -S then gdb

 target remote localhost:1234
 layout asm
 b *0x7c00
 c

ASM reg

https://en.wikibooks.org/wiki/X86_Assembly/X86_Architecture

In 16 bits

There is 4 main 16bits reg: AX, BX, CX, DX. You can access the 8 MSB from AX with AH and the 8 LSB with AL.( BH,BL, CH, CL)

SI and DI are 16bits index register often used for pointer but can contains data.

SP is stack pointer, BP is base pointer

AX(AH, AL), BX(BH, BL), CX(CH, CL), DX(DH, DL), SI, DI, SP, BP

In 32bits

Main register are "Extended" to 32bits but 16bits of 8bits direct access is not possible anymore.

EAX, EBX, ECX, EDX, ESI, EDI, ESP, EBP

In 64bits

Prefixed by R RAX, RBX, RCX, RDX, RSI, RDI, RSP, RBP

Bios Memory

Address range	Description
0x0 - 0x03FF	IVT
0x400 - 0x4FF	BIOS Data
0x500 - 0x7BFF	Unused
0x7C00 - 0x7D77	Bootloader
0x7E00 - 0x9FFFF	Unused
0xA0000 - 0xBFFFF	Video memory
0xB0000 - 0xB7777	Video memory monochrome
0xB8000 - 0xBFFFF	Video memory color
0xC0000 - 0xC7FFF	BIOS ROM
0x80000 - 0xEFFFF	BIOS shadow memory
0xF0000 - 0xFFFFF	BIOS System

Interrupt Vector Table

INT_NUM	Short Description PM
0x00	Division by zero
0x01	Debugger
0x02	NMI
0x03	Breakpoint
0x04	Overflow
0x05	Bounds
0x06	Invalid Opcode
0x07	Coprocessor not available
0x08	Double fault
0x09	Coprocessor Segment Overrun (386 or earlier only)
0x0A	Invalid Task State Segment
0x0B	Segment not present
0x0C	Stack Fault
0x0D	General protection fault
0x0E	Page fault
0x0F	reserved
0x10	Math Fault
0x11	Alignment Check
0x12	Machine Check
0x13	SIMD Floating-Point Exception
0x14	Virtualisation Exception
0x15	Control Protection Exception

BIOS IRQ

https://en.wikipedia.org/wiki/BIOS_interrupt_call