VESA.nasm

; GDT Layout:

; 00 - NULL
; 08 - 64 Code
; 10 - 64 Data
; 18 - 16 Code (0000 - FFFF)
; 20 - 16 Data (0000 - FFFF)
; 28 - 32 Code (Flat)
; 30 - 32 Data (Flat)

section .text
bits 32
global SVGA_INFO
global SVGA_MODE_INFO
global SVGA_SET_MODE
global VBE_DC_CHECK
global VBE_DC_EDID

SVGA_INFO:
    pusha
    mov eax, 0x4F00
    mov edi, [esp + 36]
    jmp WORD 0x18:DoVBECall

SVGA_MODE_INFO:
    pusha
    mov eax, 0x4F01
    mov edi, [esp + 36]
    mov ecx, [esp + 40]
    jmp WORD 0x18:DoVBECall

SVGA_SET_MODE:
    pusha
    mov eax, 0x4F02
    mov edi, [esp + 36]
    mov ebx, [esp + 40]
    jmp WORD 0x18:DoVBECall

VBE_DC_CHECK:
    pusha
    mov eax, 0x4F15
    xor bl, bl
    jmp WORD 0x18:DoVBECall

VBE_DC_EDID:
    pusha
    mov eax, 0x4F15
    mov bl, 1
    xor cx, cx
    mov edi, [esp + 36]
    jmp WORD 0x18:DoVBECall

Return:
    mov dx, 0x30
    mov ds, dx
    mov es, dx
    mov ss, dx
    xor ax, 0x4F
    mov [esp + 28], eax
    popa
    ret

bits 16
DoVBECall:
    mov dx, 0x20
    mov ds, dx
    mov es, dx
    mov ss, dx
    mov edx, cr0
    and dl, 0xFE
    mov cr0, edx
    jmp 0:.CallVBE
    .CallVBE:
        xor dx, dx
        mov ds, dx
        mov es, dx
        mov ss, dx
        sti
        int 0x10
        cli
        mov edx, cr0
        or dl, 1
        mov cr0, edx
        jmp 0x28:Return