initial commit

bootloader/bootloader.asm

@@ -0,0 +1,89 @@
+[BITS 16]
+[org 0x7c00]
+
+mov [BOOT_DEVICE], dl
+
+; setup stack
+mov bp, 0x9000
+mov sp, bp
+
+; Set video mode (640 x 480 @ 16 colors)
+mov ah, 0x00
+mov al, 0x12
+int 0x10
+
+call load_kernel
+call switch_to_32bit
+
+load_kernel:
+		mov bx, 0x1000        ; Destination address
+		mov dh, 2             ; Sector number
+		mov dl, [BOOT_DEVICE] ; Drive Number
+
+		mov al, dh
+		mov ch, 0x00 ; Cylinder number
+		mov cl, 0x02 ; Start from sector 2, sector 1 is our bootloader
+		mov ah, 0x02 ; Set read mode 
+		mov dh, 0x00
+
+		int 0x13
+		ret
+
+gdtp:
+		dw gdt_end - gdt_start - 1
+		dw gdt_start
+
+gdt_start:
+		dq 0x0
+gdt_code_segment:
+		dw 0xFFFF         ; Limit (16-bit) (set to 0xFFFF for maximum)
+		dw 0x0            ; Base (16-bit)
+		db 0x0            ; Base (8-bit)
+		db 10011010b      ; Access flags
+		db 11001111b      ; Granularity flags (set to 0xCF for 4 KB granularity)
+		db 0x0            ; Segment bits
+gdt_data_segment:
+		dw 0xFFFF         ; Limit (16-bit) (set to 0xFFFF for maximum)
+		dw 0x0            ; Base (16-bit)
+		db 0x0            ; Base (8-bit)
+		db 10010010b      ; Access flags
+		db 11001111b      ; Granularity flags (set to 0xCF for 4 KB granularity)
+		db 0x0            ; Segment bits
+gdt_end:
+
+GDT_CODE_SEG_ADDR equ gdt_code_segment - gdt_start
+GDT_DATA_SEG_ADDR equ gdt_data_segment - gdt_start
+
+switch_to_32bit:
+		; Disable interrupts and setup gdt 
+		cli
+		lgdt [gdtp]
+
+		; Set PE (Protection Enable) bit in CR0
+		mov eax, cr0
+		or eax, 0x01
+		mov cr0, eax
+		jmp GDT_CODE_SEG_ADDR:init_32bit
+
+[BITS 32]
+init_32bit:
+		mov ax, GDT_DATA_SEG_ADDR
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    mov ss, ax
+
+		mov ebp, 0x90000
+		mov esp, ebp
+
+		call init_kernel
+
+init_kernel:
+		call 0x1000
+		jmp $
+
+BOOT_DEVICE db 0x00
+
+times 510 - ($ - $$) db 0 ; make sure file is 510 bytes in size
+dw 0xAA55                 ; write boot signature