11_5.asm

.eqv KEY_CODE   0xFFFF0004       # ASCII code fromkeyboard, 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
.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 $t0 = 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 keyShowKey:
	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