Assignment No. 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

Progressive Education Society's
MODERN COLLEGE OF ENGINEERING, PUNE-05.
Department of Computer Engineering

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
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 ;to store 48-bit LDTR value-resd(32-bit) and resw(16-bit).
resw 1
tr resw 1
msw resd 1
result resb 4
%macro write 2
mov rax,1
mov rdi,1
mov rsi,%1
mov rdx,%2
syscall
%endmacro

section .text
global _start
_start:
write introMsg,introMsgLen
smsw eax ; This instruction is used to store the contents of the MSW register into the EAX register.
bt eax,0 ; copy the 0 th least significant bit from EAX to the carry flag.
jc protected_mode ;if CF is set ,processor is in protected mode

write realMsg,realMsgLen
jmp endOfProgram

protected_mode :
write protectedMsg , protectedMsgLen
write proMsg , proMsgLen
sgdt [gdtr] ; Stores the content of the global descriptor table register (GDTR) in the destination
operand gdtr
sldt [ldtr] ;store LDTR
str [tr]
smsw [msw]
write gdtrMsg,gdtrMsgLen
mov bx,[gdtr+4] ;move upper half of gdtr in bx reg.
call disp
mov bx,[gdtr+2]
call disp
write colon , colonLen
mov bx,[gdtr]
call disp
write ldtrMsg,ldtrMsgLen
mov bx,[ldtr]
call disp
write idtrMsg,idtrMsgLen
mov bx,[idtr+4]
call disp
mov bx,[idtr+2]
call disp
write colon , colonLen
mov bx,[idtr]
call disp
write trMsg,trMsgLen
mov bx,[tr]
call disp
write mswMsg,mswMsgLen
mov bx,[msw+2] ;upper half of CR0 or MSW
call disp
mov bx,[msw]
call disp

endOfProgram:
mov rax, 60
mov rdi, 0
syscall

disp:
mov rdi, result ;point rdi to result variable
mov cx,04 ;load count of rotation in cl

up1:
rol bl,04 ;rotate number left by four bits
mov dl,bl ;move lower byte in dl
and dl,0fh ; get only LSB
cmp dl,09h ;compare with 39h
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 ;store ascii code in result variable
inc rdi ;point to next byte
dec cx ;decrement the count of digits to display
jnz up1 ;if not zero jump to repeat
write result , 4
ret