Add boot.asm
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@ -0,0 +1,120 @@
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[bits 16] ; Set to 16-bit mode
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[org 0x7C00] ; BIOS loads the bootloader at this address
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; Define GDT
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gdt_start:
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dw 0x0000 ; Limit (low)
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dw 0x0000 ; Base (low)
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db 0x00 ; Base (mid)
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db 0x9A ; Access byte: Present, ring 0, executable
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db 0xCF ; Flags: Granularity, 32-bit
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db 0x00 ; Base (high)
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dw 0x0000 ; Limit (low)
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dw 0x0000 ; Base (low)
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db 0x00 ; Base (mid)
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db 0x92 ; Access byte: Present, ring 0, writable
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db 0xCF ; Flags: Granularity, 32-bit
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db 0x00 ; Base (high)
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gdt_descriptor:
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dw gdt_end - gdt_start - 1 ; Limit
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dd gdt_start ; Base address
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gdt_end:
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start:
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cli ; Disable interrupts
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lgdt [gdt_descriptor] ; Load GDT
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mov eax, cr0 ; Read CR0 register
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or eax, 1 ; Set PE bit (Protected Mode Enable)
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mov cr0, eax ; Write back to CR0
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jmp 0x08:protected_mode_entry ; Far jump to flush the pipeline
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protected_mode_entry:
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mov ax, 0 ; Set data segment to the new segment
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mov ds, ax ; Load data segment register
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mov es, ax ; Load extra segment register
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mov fs, ax ; Load fs segment register
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mov gs, ax ; Load gs segment register
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call clear_screen ; Clear the screen
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mov si, welcome_message
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call print_string_protected
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command_loop:
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mov si, prompt_message
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call print_string_protected
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call read_input
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cmp al, 'h' ; Check for 'h' command (help)
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je print_help
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cmp al, 'q' ; Check for 'q' command (quit)
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je quit_terminal
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cmp al, 'f' ; Check for 'f' command (heckerfetch)
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je heckerfetch
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mov si, unknown_command_message
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call print_string_protected
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jmp command_loop ; Repeat the command loop
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print_help:
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mov si, help_message
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call print_string_protected
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jmp command_loop ; Return to command loop
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heckerfetch:
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mov si, heckerfetch_message
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call print_string_protected
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jmp command_loop ; Return to command loop
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quit_terminal:
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mov si, goodbye_message
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call print_string_protected
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jmp hang ; Hang the system
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; Function to read a character from keyboard input
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read_input:
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xor eax, eax ; Clear EAX for reading character input
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int 0x16 ; Call BIOS interrupt to read a character into AL
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ret ; Return with character in AL
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; Function to print a string in protected mode using VGA text buffer
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print_string_protected:
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mov edi, 0xb8000 ; VGA text buffer address
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.next_char:
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lodsb ; Load byte at DS:SI into AL and increment SI
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cmp al, 0 ; Check for null terminator
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je .done ; If null, we are done
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mov [edi], ax ; Write character and attribute (white on black)
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add edi, 2 ; Move to next character cell
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jmp .next_char ; Repeat for next character
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.done:
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ret ; Return from function
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; Function to clear the screen in protected mode
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clear_screen:
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xor di, di ; Start from the beginning of the VGA buffer
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mov cx, 80 * 25 ; Number of characters in a standard text mode screen
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mov ax, 0x07 ; Attribute for white on black background
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.fill_screen:
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stosw ; Store word in [ES:DI] and increment DI by 2
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loop .fill_screen ; Repeat until CX is zero
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ret ; Return from function
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; Data section for messages
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welcome_message db 'Welcome to the HeckerOS!', 0
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prompt_message db 'Enter command (h for help, q to quit, f for heckerfetch): ', 0
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help_message db 'Available commands: h (help), q (quit), f (heckerfetch)', 0
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unknown_command_message db 'Unknown command! Try again.', 0
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goodbye_message db 'Goodbye!', 0
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heckerfetch_message db 'OS: HeckerOS Beta, CPU: HeckerSoft Generic CPU 0GHZ', 'Host: HeckerSoft Unknown Host', 0
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; Bootloader signature (must be present)
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times 510 - ($ - $$) db 0 ; Fill the rest of the sector with zeros
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dw 0xAA55 ; Boot signature
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hang:
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jmp hang ; Jump to hang indefinitely
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