bootloader.asm

;----------------------------------------------;
;
; The BoneOS Stage 2 Bootloader
; -----------------------------
;
;
; Contributors : @amanuel2
;
;
;----------------------------------------------;


 
  stage2:

	MOV si, SECONDSTAGEXECUTION
	CALL printfbln	
	;-------------------
	;Load Kernel
	;-------------------
	
	
	; enable A20 gate
	enable_A20: ; Enabling A20 Line For Full Memory
			cli ; Stop Interupts before doing so
	 
			call    a20wait ; a20wait call
			mov     al,0xAD ; Send 0xAD Command to al register
			out     0x64,al ; Send command 0xad (disable keyboard).
	 
			call    a20wait ; When controller ready for command
			mov     al,0xD0 ; Send 0xD0 Command to al register
			out     0x64,al ; Send command 0xd0 (read from input)
	 
			call    a20wait2 ; When controller ready for command
			in      al,0x60 ; Read input from keyboard
			push    eax ; Save Input by pushing to stack
	 
			call    a20wait ; When controller ready for command
			mov     al,0xD1 ; mov 0xD1 Command to al register
			out     0x64,al ; Set command 0xd1 (write to output)
	 
			call    a20wait ; When controller ready for command
			pop     eax ; Pop Input from Keyboard
			or      al,2 ; Mov 0xD3 to al register
			out     0x60,al ; Set Command 0xD3
	 
			call    a20wait ; When controller ready for command
			mov     al,0xAE ; Mov Command 0xAE To al register
			out     0x64,al ; Write command 0xae (enable keyboard)
	 
			call    a20wait ; When controller ready for command
			sti ; Enable Interrupts after enabling A20 Line
			ret
		 
				a20wait:
					in      al,0x64 ; input from 0x64 port, goes to al register
					test    al,2 ; compares al register with 2
					jnz     a20wait ; If it is zero loop again
					ret
			 
			 
				a20wait2:
					in      al,0x64 ; input from 0x64 port, goes to al register
					test    al,1 ; compares al register with 2
					jz      a20wait2 ; If it is zero loop again
					ret	
	;load a GDT
	; enter pmode
	loadgdt:
		cli				; disable int
    	LGDT [gdt_descriptor]                   ; Load global descriptor table for protected mode

		MOV EAX, CR0                            ; Move CR0 to GP register
		OR EAX, 0x1                             ; Set first bit to switch to protected mode
		MOV CR0, EAX                            ; Update CR0 from GP register to complete switch
	
		JMP gdt_codeSeg:start32                 ; Jump to start of 32-bit code
		
		[BITS 32]                               ; 32-bit protected mode
		start32:                                ; Jump target for start of protected mode code

		MOV AX, gdt_dataSeg                     ; Update segments for protected mode as defined in GDT
		MOV DS, AX
		MOV SS, AX
		MOV ES, AX
		MOV FS, AX
		MOV GS, AX

		MOV EBP, 0x90000                        ; Set stack base at top of free space
		MOV ESP, EBP                            ; Set stack pointer at base of stack

		CALL ADDR_KERNEL_OFFSET                 ; Begin executing the kernel

		ADDR_KERNEL_OFFSET EQU 0x1000           ; Define location for kernel in memory
	; jump to kernel
	
    cli
    hlt
	
    times ((0x400) - ($ - $$)) db 0x00