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bits 16
org 0x7c3e
kernel_sectors equ 64
kernel_segment equ 0x3000
support_flags equ 0x4000
pci_hw_char equ 0x4001
pci_ver equ 0x4002
last_pci_bus equ 0x4004
bios_mmap_len equ 0x4006
vbe_mode equ 0x4008
vbe_block equ 0x4200
vbe_mode_info equ 0x4400
pci_support equ 0x80
pae_support equ 0x40
in al, 0x92
or al, 0x02
out 0x92, al
xor ax, ax
mov ss, ax
mov sp, 0x8000
mov ax, kernel_segment
mov es, ax
mov ax, 0x0200 + kernel_sectors
xor bx, bx
mov cx, 0x0002
xor dh, dh
int 0x13
mov ax, 0xb101
int 0x1a
cmp edx, 0x20494350
jne no_pci
test ah, ah
jnz no_pci
mov byte [support_flags], pci_support
mov byte [pci_hw_char], al
mov word [pci_ver], bx
mov byte [last_pci_bus], cl
no_pci:
mov eax, 1
cpuid
test dl, 0x40
jz no_pae
or byte [support_flags], pae_support
no_pae:
mov ax, 0x1000
mov es, ax
xor di, di
mov edx, 0x534d4150
xor ebx, ebx
mmap_loop:
mov eax, 0xe820
mov ecx, 24
int 0x15
jc mmap_end
add di, 24
test ebx, ebx
jnz mmap_loop
mmap_end:
mov word [bios_mmap_len], di
xor ax, ax
mov es, ax
mov di, vbe_block
mov ah, 0x4f
mov dword [di], 0x32454256;'VBE2'
int 0x10
cmp dword [di], 0x41534556;'VESA'
jne no_vbe
mov bx, word [di + 0x0e]
mov ax, word [di + 0x10]
mov fs, ax
xor esi, esi
mov bp, 0xffff
mov di, 0x5000
vbe_loop:
max_height equ 800
;fs:bx is mode pointer
;esi is highest resolution yet (width * height)
;bp is that mode's number
;uses 0x5000 - 0x50ff as mode info buffer
;skips those without byte-aligned pixels
mov cx, word [fs:bx]
cmp cx, 0xffff
je got_highest_vbe
add bx, 4
mov ax, 0x4f01
int 0x10
mov al, byte [di]
not al
test al, 0x9a
jnz vbe_loop
mov dx, word [di + 0x14];height
cmp dx, max_height
jg vbe_loop
mov ax, word [di + 0x12];width
mul dx
shl edx, 16
mov dx, ax
xor eax, eax
mov al, byte [di + 0x19];bpp
test al, 0x07
jnz vbe_loop
mul edx
cmp eax, esi
jle vbe_loop
mov esi, eax
mov bp, cx
jmp vbe_loop
got_highest_vbe:
cmp bp, 0xffff
je no_vbe
mov cx, bp
mov ax, 0x4f01
mov di, vbe_mode_info
int 0x10
or ch, 0x40
mov word [vbe_mode], cx
mov ax, 0x4f02
mov bx, cx
int 0x10
cli
lgdt [gdt]
mov eax, cr0
or al, 0x01
mov cr0, eax
jmp 0x10:pmode
no_vbe:
xor ax, ax
mov es, ax
mov ax, 0x1300
mov bx, 0x004f
mov cx, no_vbe_str.len
xor dx, dx
mov bp, no_vbe_str
int 0x10
real_halt:
hlt
jmp real_halt
no_vbe_str:
db "NO VBE2!"
.len equ $ - no_vbe_str
bits 32
pmode:
mov ax, 0x18
mov ds, ax
mov es, ax
mov ss, ax
mov esp, 0x00040000
xor ebp, ebp
call kernel_segment * 16
halt:
hlt
jmp halt
times $$ + 510 - 0x3e - $ - (gdt.e - gdt) db 0
gdt:
dw .e - .t
dd .t
.t:
dq 0x0000_0000_0000_0000;0x00: null
dq 0x0040_8900_4f98_0068;0x08: tss, 0x4f98
dq 0x00cf_9a00_0000_ffff;0x10: kernel code
dq 0x00cf_9200_0000_ffff;0x18: kernel data
dq 0x00cf_fa00_0000_ffff;0x20: user code
dq 0x00cf_f200_0000_ffff;0x28: user data
.e:
dw 0xaa55
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