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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
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, 0x7ffc
mov ax, 0x0013
int 0x10
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 [0x4006], di
cli
lgdt [gdt]
mov eax, cr0
or al, 0x01
mov cr0, eax
jmp 0x10:pmode
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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