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global kboot
global register_isr
extern kmain
extern timer_init
; Multiboot header
section .mboothdr
mboot_hdr:
align 4
dd 0x1BADB002
dd 0x00
dd - (0x1BADB002 + 0x00)
section .text
kboot:
cli
call flush_gdt
call flush_idt
call timer_init
call kmain
cli
hlt
gdt:
; null descriptor
dq 0
; kernel code segment
dw 0xFFFF ; limit (bits 0-15)
dw 0x0000 ; base (bits 0-15)
db 0x00 ; base (bits 16-23)
db 0x9A ; access byte
db 0xCF ; flags / limit (bits 16-19)
db 0x00 ; base (bits 24-31)
; kernel data segment
dw 0xFFFF
dw 0x0000
db 0x00
db 0x92
db 0xCF
db 0x00
; userspace code segment
dw 0xFFFF
dw 0x0000
db 0x00
db 0xFA
db 0xCF
db 0x00
; userspace data segment
dw 0xFFFF
dw 0x0000
db 0x00
db 0xF2
db 0xCF
db 0x00
gdtp:
dw ($-gdt-1)
dd gdt
flush_gdt:
push ebp
mov ebp, esp
lgdt [gdtp]
mov ax, 0x10
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
jmp 0x08:.end
.end:
pop ebp
ret
idt:
times (256*8) db 0
idtp:
dw ($-idt-1)
dd idt
int_handler:
iret
irq_handler:
iret
flush_idt:
push ebp
mov ebp, esp
mov ecx, 0
mov edx, idt
.loop:
mov eax, int_handler
cmp ecx, 0x20
jl .skip
cmp ecx, 0x2f
jg .skip
mov eax, irq_handler
.skip:
mov [edx], ax
mov word [edx+2], 0x08
mov byte [edx+4], 0
mov byte [edx+5], 0x8E
shr eax, 16
mov [edx+6], ax
add edx, 8
inc ecx
cmp ecx, 256
je .end
jmp .loop
.end:
lidt [idtp]
call pic_init
sti
pop ebp
ret
; void register_isr(uint8_t n, void *handler);
register_isr:
push ebp
mov ebp, esp
mov edx, [ebp+8]
shl edx, 3
add edx, idt
mov eax, [ebp+12]
mov [edx], ax
add edx, 6
shr eax, 16
mov [edx], ax
pop ebp
ret
pic_init:
push ebp
mov ebp, esp
mov al, 0x11
out 0x20, al
out 0xA0, al
mov al, 0x20
out 0x21, al
out 0xA1, al
mov al, 0x04
out 0x21, al
mov al, 0x02
out 0xA1, al
mov al, 0x01
out 0x21, al
out 0xA1, al
mov al, 0xFF
out 0x21, al
out 0xA1, al
pop ebp
ret
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