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kernel.asm
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bits 32
section .text
;multiboot spec
align 4
dd 0x1BADB002 ;magic
dd 0x00 ;flags
dd - (0x1BADB002 + 0x00) ;checksum. m+f+c should be zero
global start
global keyboard_handler
global read_port
global write_port
global load_idt
extern kmain ;this is defined in the c file
extern keyboard_handler_main
gdt:
gdt_null:
dq 0
gdt_code:
dw 0FFFFh
dw 0
db 0
db 10011010b
db 11001111b
db 0
gdt_data:
dw 0FFFFh
dw 0
db 0
db 10010010b
db 11001111b
db 0
gdt_end:
gdt_desc:
dw gdt_end - gdt - 1
dd gdt
load_gdt:
cli ;disable interrupts
lgdt [gdt_desc] ;load GDT
sti ;enable interrupts
read_port:
mov edx, [esp + 4]
;al is the lower 8 bits of eax
in al, dx ;dx is the lower 16 bits of edx
ret
write_port:
mov edx, [esp + 4]
mov al, [esp + 4 + 4]
out dx, al
ret
load_idt:
mov edx, [esp + 4]
lidt [edx]
sti ;turn on interrupts
ret
keyboard_handler:
call keyboard_handler_main
iretd
start:
cli ;block interrupts
;we must load gdt
lgdt [gdt_desc]
jmp 0x0008:fix_cs
fix_cs:
mov ax, 0x0010
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax
mov esp, stack_space ;set stack pointer
call kmain
jmp $ ;halt the CPU
section .bss
resb 8192; 8KB for stack
stack_space: