102 lines
3 KiB
NASM
102 lines
3 KiB
NASM
[bits 32]
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%define VIDMEM 0xB8000 ; Video memory mapped
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%define COLUMNS 80 ; Height of screen
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%define ROWS 25 ; Width of screen
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%define CHAR_ATTRIB 0x02 ; Character attribute
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; Prints a character
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; Input:
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; BL - The character to print
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print_char_32:
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pusha
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mov edi, VIDMEM ; Let EDI point to the start of video memory
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xor eax, eax ; Clear EAX
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mov ecx, COLUMNS
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mov al, byte [boot_parameters.cursor_pos_y] ; Get the y position
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mul ecx ; Multiply by the number of columns (EAX = y * COLUMNS)
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xor ecx, ecx
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mov cl, byte [boot_parameters.cursor_pos_x] ; Get the x position
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add eax, ecx ; Add the x position to (y * COLUMS)
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shl eax, 1 ; Multiply by 2 as 2 bytes per character
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add edi, eax ; Add the offset to the video memory address
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cmp bl, 0x0A ; Is it a new line
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je short .new_line
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mov dl, bl ; Get the character to print
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mov dh, CHAR_ATTRIB ; Add the character attribute
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mov word [edi], dx ; Write to the video memory
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inc byte [boot_parameters.cursor_pos_x] ; Increment the x position
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jmp short .print_done
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.new_line:
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mov byte [boot_parameters.cursor_pos_x], 0 ; Set cursor to beginning of line
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inc byte [boot_parameters.cursor_pos_y] ; Increment new line
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.print_done:
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popa
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ret
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; Print a null terminated string to the screen
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; Input:
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; ESI - Pointer to the string to print
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print_string_32:
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pusha
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.print_loop:
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mov bl, byte [esi] ; Get the character to print
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cmp bl, 0 ; Is it null
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je short .print_end ; Then finish
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call print_char_32 ; Print the character
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inc esi ; Increment to next character
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jmp short .print_loop
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.print_end:
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mov bh, byte [boot_parameters.cursor_pos_y]
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mov bl, byte [boot_parameters.cursor_pos_x]
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call update_cursor ; Update the cursor
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popa
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ret
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; Update the cursors new position
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; Input:
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; BH - y position
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; BL - x position
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update_cursor:
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pusha
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xor eax, eax
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mov ecx, COLUMNS
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mov al, bh
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mul ecx
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add al, bl
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mov ebx, eax
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mov al, 0x0f
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mov dx, 0x03D4
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out dx, al
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mov al, bl
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mov dx, 0x03D5
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out dx, al
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xor eax, eax
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mov al, 0x0e
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mov dx, 0x03D4
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out dx, al
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mov al, bh
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mov dx, 0x03D5
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out dx, al
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popa
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ret
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