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https://github.com/cfenollosa/os-tutorial.git
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53 lines
1.5 KiB
NASM
53 lines
1.5 KiB
NASM
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; Identical to lesson 13's boot sector, but the %included files have new paths
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[org 0x7c00]
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KERNEL_OFFSET equ 0x1000 ; The same one we used when linking the kernel
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mov [BOOT_DRIVE], dl ; Remember that the BIOS sets us the boot drive in 'dl' on boot
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mov bp, 0x9000
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mov sp, bp
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mov bx, MSG_REAL_MODE
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call print
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call print_nl
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call load_kernel ; read the kernel from disk
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call switch_to_pm ; disable interrupts, load GDT, etc. Finally jumps to 'BEGIN_PM'
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jmp $ ; Never executed
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%include "boot/print.asm"
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%include "boot/print_hex.asm"
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%include "boot/disk.asm"
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%include "boot/gdt.asm"
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%include "boot/32bit_print.asm"
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%include "boot/switch_pm.asm"
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[bits 16]
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load_kernel:
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mov bx, MSG_LOAD_KERNEL
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call print
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call print_nl
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mov bx, KERNEL_OFFSET ; Read from disk and store in 0x1000
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mov dh, 31 ; Our future kernel will be larger, make this big
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mov dl, [BOOT_DRIVE]
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call disk_load
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ret
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[bits 32]
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BEGIN_PM:
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mov ebx, MSG_PROT_MODE
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call print_string_pm
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call KERNEL_OFFSET ; Give control to the kernel
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jmp $ ; Stay here when the kernel returns control to us (if ever)
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BOOT_DRIVE db 0 ; It is a good idea to store it in memory because 'dl' may get overwritten
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MSG_REAL_MODE db "Started in 16-bit Real Mode", 0
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MSG_PROT_MODE db "Landed in 32-bit Protected Mode", 0
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MSG_LOAD_KERNEL db "Loading kernel into memory", 0
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MSG_RETURNED_KERNEL db "Returned from kernel. Error?", 0
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; padding
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times 510 - ($-$$) db 0
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dw 0xaa55
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