mirror of
https://github.com/gbowne1/ClassicOS.git
synced 2025-10-13 13:15:07 -07:00
fixing the keyboard and bootloader so that its 2 stage again
This commit is contained in:
@@ -1,67 +1,230 @@
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; ==============================================================================
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; boot.asm - First Stage Bootloader (CHS Based)
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; ==============================================================================
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[BITS 16]
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[ORG 0x7C00]
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start:
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cli
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cli ; Disable interrupts
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mov [bootdev], dl ; Save boot device number (from BIOS in DL)
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; Setup stack safely below EBDA area (choose 0x0000:0x7A00)
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xor ax, ax ; AX = 0
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mov ss, ax ; Stack segment = 0x0000
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mov sp, 0x7A00 ; Stack offset = 0x7A00
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; Initialize DS, ES for zero-based segments
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xor ax, ax
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mov ds, ax
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mov es, ax
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mov ss, ax
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mov sp, 0x7C00
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; Load second-stage bootloader (boot1.asm) to 0x7E00
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mov si, 0x7E00 ; Destination offset (ES already zero, so physical 0x7E00)
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mov al, 1 ; Number of sectors to read (adjust if needed)
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mov cl, 1 ; Starting sector (CHS - sector number, 1-based)
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call read_chs
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jc disk_error ; Jump if carry set (read error)
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; Load kernel to 0x100000 (1 MB)
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mov si, 0x0000 ; Destination offset
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mov ax, 0x1000 ; ES = 0x1000 (0x1000:0x0000 = 1 MB)
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mov es, ax
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xor bx, bx
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mov al, 16 ; Number of sectors for kernel (example)
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mov cl, 2 ; Starting sector (adjust as per your disk layout)
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call read_chs
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jc disk_error
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; Memory Validation: Verify checksum of second stage bootloader
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mov si, 0x7E00 ; Start of second stage
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mov cx, 512 ; Size in bytes (adjust if more sectors loaded)
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call verify_checksum
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jc disk_error ; Jump if checksum fails
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; Enable A20 line
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call enable_a20
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jc a20_error ; Jump if A20 enable fails
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; Setup Global Descriptor Table
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call setup_gdt
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; Switch to protected mode and jump to second stage at 0x08:0x7E00
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call switch_to_pm
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; ----------------------
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; A20 Gate Enable (Fast method)
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disk_error:
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mov si, disk_error_msg
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call print_string_16
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jmp halt
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a20_error:
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mov si, a20_error_msg
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call print_string_16
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jmp halt
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; ----------------------------------------------------------------
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; Verify Checksum Routine
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; Uses SI = start address, CX = byte count
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; Simple XOR checksum over bytes, expects result 0
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verify_checksum:
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push ax
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push bx
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push di
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mov di, si
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xor al, al
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xor bx, bx
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.verify_loop:
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lodsb
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xor bl, al
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loop .verify_loop
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test bl, bl
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jz .checksum_ok
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stc ; Set carry on checksum error
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jmp .done
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.checksum_ok:
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clc ; Clear carry on success
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.done:
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pop di
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pop bx
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pop ax
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ret
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; ----------------------------------------------------------------
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; CHS Disk Read Routine
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; AL = number of sectors
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; CL = starting sector (1-based)
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; SI = destination offset (Segment:ES already set)
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read_chs:
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pusha
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push dx
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mov cx, 5
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.retry:
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mov ah, 0x02 ; BIOS read sector
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mov dl, [bootdev] ; Drive number
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int 0x13
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jc .error ; Carry flag set = error
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pop dx
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popa
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ret
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.error:
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dec cx
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jz disk_error
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xor ah, ah
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int 0x13
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jmp .retry
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; ----------------------------------------------------------------
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enable_a20:
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; Fast A20 gate method
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in al, 0x92
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or al, 0x02
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out 0x92, al
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; Fallback method (keyboard controller)
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jc .fallbackenable_a20:
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; Fast A20 method
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in al, 0x92
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or al, 0x02
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and al, 0xFE ; Clear bit 0 to avoid fast A20 issues on some systems
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out 0x92, al
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; Verify A20
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call check_a20
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jnc .done
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; Fallback method
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mov al, 0xAD
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out 0x64, al
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; ... (rest of keyboard controller code)
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.done:
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ret
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; ----------------------
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; Set up a minimal GDT
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check_a20:
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in al, 0x64 ; Read keyboard controller status
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test al, 0x02 ; Check if input buffer is full
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jnz check_a20 ; Wait until empty
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mov al, 0xD0 ; Command: read output port
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out 0x64, al
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.wait_output:
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in al, 0x60 ; Read output port value
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test al, 0x02 ; Check A20 gate bit (bit 1)
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jnz .a20_enabled ; If set, A20 enabled
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xor al, al ; Clear carry to indicate failure
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stc ; Set carry for failure, jc will jump
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ret
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.a20_enabled:
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clc ; Clear carry flag to indicate success
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ret
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.fallback:
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mov al, 0xAD
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out 0x64, al
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mov al, 0xD0
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out 0x64, al
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in al, 0x60
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or al, 0x02
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mov al, 0xD1
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out 0x64, al
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mov al, 0xAE
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out 0x64, al
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ret
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; ----------------------------------------------------------------
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gdt_start:
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dq 0x0000000000000000 ; null descriptor
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dq 0x00CF9A000000FFFF ; code segment descriptor
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dq 0x00CF92000000FFFF ; data segment descriptor
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dq 0x0000000000000000 ; Null descriptor
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dq 0x00CF9A000000FFFF ; 32-bit code segment (selector 0x08)
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dq 0x00CF92000000FFFF ; 32-bit data segment (selector 0x10)
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dq 0x00009A000000FFFF ; 16-bit code segment for real mode (selector 0x18)
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gdt_descriptor:
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dw gdt_end - gdt_start - 1 ; size of GDT
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dd gdt_start ; address of GDT
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dw gdt_end - gdt_start - 1
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dd gdt_start
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gdt_end:
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setup_gdt:
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lgdt [gdt_descriptor]
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ret
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; ----------------------
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; Switch to Protected Mode
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; ----------------------------------------------------------------
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switch_to_pm:
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cli
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mov eax, cr0
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or eax, 1
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mov cr0, eax
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jmp 0x08:protected_mode_entry
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; ----------------------
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; 32-bit Protected Mode Entry Point
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[BITS 32]
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protected_mode_entry:
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mov ax, 0x10 ; data segment selector
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax
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mov esp, 0x90000
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jmp 0x08:0x7E00
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; Kernel is assumed to be loaded at 0x100000
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jmp 0x08:0x100000
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; ----------------------------------------------------------------
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print_string_16:
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.loop:
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lodsb
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or al, al
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jz .done
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mov ah, 0x0E
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int 0x10
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jmp .loop
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.done:
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ret
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disk_error_msg db "Disk error!", 0
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a20_error_msg db "A20 error!", 0
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halt:
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cli
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hlt
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bootdev db 0
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sectors_per_track dw 63
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heads_per_cylinder dw 255
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; ----------------------
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; Boot signature
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times 510 - ($ - $$) db 0
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dw 0xAA55
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