lab11_ex5.asm

.eqv KEY_CODE   0xFFFF0004       # ASCII code from keyboard, 1 byte 
.eqv KEY_READY  0xFFFF0000       # =1 if has a new keycode ? 
                                 # Auto clear after lw 
.eqv DISPLAY_CODE   0xFFFF000C   # ASCII code to show, 1 byte 
.eqv DISPLAY_READY  0xFFFF0008   # =1 if the display has already to do 
                                 # Auto clear after sw 
.eqv  MASK_CAUSE_KEYBOARD   0x0000034     # Keyboard Cause 

.data
Messenger: .asciiz "It is the first letter of my name\n"
 
.text     
             li   $k0, KEY_CODE 
             li   $k1, KEY_READY 
             li   $s0, DISPLAY_CODE 
             li   $s1, DISPLAY_READY  
loop:        nop 
WaitForKey:  lw   $t1, 0($k1)            # $t1 = [$k1] = KEY_READY 
             beq  $t1, $zero, WaitForKey # if $t1 = 0 then Polling             
MakeIntR:    teqi $t1, 1          # if $t1 = 1 then raise an Interrupt 
             j loop     
#----------------------------------------------------------------- 
# Interrupt subroutine 
#----------------------------------------------------------------- 
.ktext 0x80000180 
get_caus:    mfc0  $t1, $13              # $t1 = Coproc0.cause 
IsCount:     li    $t2, MASK_CAUSE_KEYBOARD# if Cause value confirm Keyboard.. 
             and   $at, $t1,$t2 
             beq   $at,$t2, Counter_Keyboard 
             j    end_process 
Counter_Keyboard: 
ReadKey:     lw   $t0, 0($k0)            # $t0 = [$k0] = KEY_CODE 

WaitForDis:  lw   $t2, 0($s1)            # $t2 = [$s1] = DISPLAY_READY 
             beq  $t2, $zero, WaitForDis # if $t2 == 0 then Polling              
Encrypt:     #addi $t0, $t0, 1           # change input key 
		beq $t0, 0x44, ShowMessenger
		beq $t0, 0x64, ShowMessenger
		j ShowKey
ShowMessenger: #sw $t0, 0($s0)             # show key 
             	#nop 
		li $v0, 4
		la $a0, Messenger
		syscall
		nop 
		nop
		j end_process
ShowKey:     sw $t0, 0($s0)             # show key 
             nop                
end_process:                         
next_pc:     mfc0    $at, $14       # $at <= Coproc0.$14 = Coproc0.epc 
             addi    $at, $at, 4    # $at = $at + 4 (next instruction) 
	      mtc0    $at, $14       # Coproc0.$14 = Coproc0.epc <= $at  
return:    eret                   # Return from exception