Assignment 6

section .data
introMsg dw "ALP to detect the operating mode of the microprocessor and display the contents of some system registers"
introMsgLen equ $- introMsg gdtrMsg db 10,10,"Contents of GDTR : ",10 gdtrMsgLen equ$ - gdtrMsg
ldtrMsg db 10,10,"Contents of LDTR : ",10
ldtrMsgLen equ $- ldtrMsg idtrMsg db 10,10,"Contents of IDTR : ",10 idtrMsgLen equ$ - idtrMsg
trMsg db 10,10,"Contents of TR : ",10
trMsgLen equ $- trMsg mswMsg db 10,10,"Contents of MSW (CR0) register : ",10 mswMsgLen equ$ - mswMsg
protectedMsg db 10,10,"The Microprocessor is in the protected mode"
protectedMsgLen equ $- protectedMsg proMsg db 10,10,"The contents of the system registers are as follows : " proMsgLen equ$ - proMsg
realMsg db 10,10,"The Microprocessor is in the real mode"
realMsgLen equ $- realMsg newline db 10,13 newlineLen equ$ - newline
colon db " : "
colonLen equ $ - colon

section .bss
gdtr resd 1 ;to store 48-bit GDTR value-resd(32-bit) and resw(16-bit)
resw 1
ldtr resw 1 ;to store 16-bit LDTR
idtr resd 1
resw 1
tr resw 1
msw resd 1
result resb 4

%macro print 2
mov rax,1
mov rdi,1
mov rsi,%1
mov rdx,%2
syscall
%endmacro

section .text
global _start

_start:
	 print introMsg,introMsgLen
	
	 smsw eax   			
	 bt eax,0     		; copy the 0th  least significant bit from EAX to the carry flag.
	 jc protected_mode	;if CF is set ,processor is in protected mode
	 
	 print realMsg,realMsgLen
	 jmp exit1
	 
	protected_mode :
		 print protectedMsg , protectedMsgLen
		 print proMsg , proMsgLen
		 sgdt [gdtr]   
		 sldt [ldtr]  		
		 str [tr]  
		 smsw [msw]
		 
		 print gdtrMsg,gdtrMsgLen
		 mov bx,[gdtr+4]  ;move upper half of gdtr in bx reg.
		 call disp
		 mov bx,[gdtr+2] 
		 call disp
		 print colon , colonLen
		 mov bx,[gdtr]
		 call disp
		 
		 print ldtrMsg,ldtrMsgLen
		 mov bx,[ldtr]
		 call disp
		 
		 print idtrMsg,idtrMsgLen
		 mov bx,[idtr+4]
		 call disp
		 mov bx,[idtr+2]
		 call disp
		 print colon , colonLen
		 mov bx,[idtr]
		 call disp
		 
		 print trMsg,trMsgLen
		 mov bx,[tr]
		 call disp
		 
		 print mswMsg,mswMsgLen
		 mov bx,[msw+2]   ;upper half of CR0 or MSW
		 call disp
		 mov bx,[msw]
		 call disp
		 
	exit1:   
		print newline, newlineLen
	    mov rax, 60
	    mov rdi, 0
	    syscall
	    
	disp: 						;ASCII conversion function
		mov rdi, result 
		mov cx,04 
		up1:
			rol bl,04 
			mov dl,bl 
			and dl,0fh 
			cmp dl,09h 
			jg add_37 ;if greater than 39h skip add 37
			add dl,30h
			jmp skip1 ;else add 30
			
		add_37: 
			add dl,37h
			
		skip1:  
			mov [rdi],dl 
			inc rdi 
			dec cx 
			jnz up1
			
			print result , 4
			
		ret