Multiboot1 Bare Bones with NASM: Difference between revisions
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Added full kernel on NASM instead of just the bootloader |
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You can then assemble boot.asm using:
<source lang="bash">nasm -felf32 boot.asm -o boot.o</source>
== Kernel ==
<source lang="asm">
BITS 32
VGA_WIDTH equ 80
VGA_HEIGHT equ 25
VGA_COLOR_BLACK equ 0
VGA_COLOR_BLUE equ 1
VGA_COLOR_GREEN equ 2
VGA_COLOR_CYAN equ 3
VGA_COLOR_RED equ 4
VGA_COLOR_MAGENTA equ 5
VGA_COLOR_BROWN equ 6
VGA_COLOR_LIGHT_GREY equ 7
VGA_COLOR_DARK_GREY equ 8
VGA_COLOR_LIGHT_BLUE equ 9
VGA_COLOR_LIGHT_GREEN equ 10
VGA_COLOR_LIGHT_CYAN equ 11
VGA_COLOR_LIGHT_RED equ 12
VGA_COLOR_LIGHT_MAGENTA equ 13
VGA_COLOR_LIGHT_BROWN equ 14
VGA_COLOR_WHITE equ 15
global kernel_main
kernel_main:
mov dh, VGA_COLOR_LIGHT_GREY
mov dl, VGA_COLOR_BLACK
call terminal_set_color
mov esi, hello_string
call terminal_write_string
jmp $
; IN = dl: y, dh: x
; OUT = dx: Index with offset 0xB8000 at VGA buffer
; Other registers preserved
terminal_getidx:
push ax; preserve registers
shl dh, 1 ; multiply by two because every entry is a word that takes up 2 bytes
mov al, VGA_WIDTH
mul dl
mov dl, al
shl dl, 1 ; same
add dl, dh
mov dh, 0
pop ax
ret
; IN = dl: bg color, dh: fg color
; OUT = none
terminal_set_color:
shl dl, 4
or dl, dh
mov [terminal_color], dl
ret
; IN = dl: y, dh: x, al: ASCII char
; OUT = none
terminal_putentryat:
pusha
call terminal_getidx
mov ebx, edx
mov dl, [terminal_color]
mov byte [0xB8000 + ebx], al
mov byte [0xB8001 + ebx], dl
popa
ret
; IN = al: ASCII char
terminal_putchar:
mov dx, [terminal_cursor_pos] ; This loads terminal_column at DH, and terminal_row at DL
call terminal_putentryat
inc dh
cmp dh, VGA_WIDTH
jne .cursor_moved
mov dh, 0
inc dl
cmp dl, VGA_HEIGHT
jne .cursor_moved
mov dl, 0
.cursor_moved:
; Store new cursor position
mov [terminal_cursor_pos], dx
ret
; IN = cx: length of string, ESI: string location
; OUT = none
terminal_write:
pusha
.loopy:
mov al, [esi]
call terminal_putchar
dec cx
cmp cx, 0
je .done
inc esi
jmp .loopy
.done:
popa
ret
; IN = ESI: zero delimited string location
; OUT = ECX: length of string
terminal_strlen:
push eax
push esi
mov ecx, 0
.loopy:
mov al, [esi]
cmp al, 0
je .done
inc esi
inc ecx
jmp .loopy
.done:
pop esi
pop eax
ret
; IN = ESI: string location
; OUT = none
terminal_write_string:
pusha
call terminal_strlen
call terminal_write
popa
ret
; Exercises:
; - Newline support
; - Terminal scrolling when screen is full
; Note:
; - The string is looped through twice on printing.
hello_string db "Hello, kernel World!", 0xA, 0 ; 0xA = line feed
terminal_color db 0
terminal_cursor_pos:
terminal_column db 0
terminal_row db 0
</source>
Similar as before, to assemble it:
<source lang="bash">nasm -felf32 kernel.asm -o kernel.o</source>
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