(Memory mapped I/O interrupt) In MARS, Write a MIPS program to implement the following single digit adder: keyboard input: X+Y= display output: X+Y=Z where X and Y are single digits (such as 2 and 7) and Z is the result (such as 9). Please use keyboard interrupt to read the keyboard input from the receiver data, compute the result Z and use polling (on the transmitter control and transmitter data) to send the output X+Y=Z to the display. To test your code, you need open the MMIO in the simulator. Goto Tools?Keyboard and Display MMIO ? make sure you press connect to MIPS to run your code. Sometimes, it is also helpful to press reset on the same screen. Dont forget to store registers when you write MIPS functions To slow down execution in the simulator, slide Run speed to max bar to the left

I found this code, but it doesnt implement addition based on keyboard input, it just copies my keystrokes to the display and nothing more. If i type 1+2= in the simulator, the program should display 1+2= followed by the result. I want to know how to make this work.

Given Code:

main: li $v0 4 la $a0 prompt syscall # Register usage: # s0 loop counter # t0 address of recv_ctrl # t1 address of recv_buffer # t2 address of trans_ctrl # t3 address of trans_buffer # t4, t5 temporaries # t6 char read from input # t7 1 => char in t6 li $s0, 3 # loop counter li $t0, 0xffff0000 # recv ctrl li $t1, 0xffff0004 # recv buf li $t2, 0xffff0008 # trans ctrl li $t3, 0xffff000c # trans buf # First, read and echo 3 lines of input by polling the IO registers, not through # interrupts: mtc0 $0, $12 # Clear IE bit in Status reg to disable interrupts l1: lw $t4, 0($t0) # Wait for receiver ready and $t4, $t4, 1 beq $t4, 0, l1 lw $t6, 0($t1) # Read character l2: lw $t4, 0($t2) # Wait for transmitter ready and $t4, $t4, 1 beq $t4, 0, l2 sw $t6, 0($t3) # Write character beq $t6, 0xa, decr # New line (nl) bne $t6, 0xd, l1 # Carriage return (cr) decr: add $s0, $s0, -1 # Decrement line counter bne $s0, 0, l1 # If not zero, get another line # Second, read and echo 3 lines of input by through interrupts: mfc0 $t4, $13 andi $t4, 0xffff00ff # Clear IP bits in Cause register mtc0 $t4, $13 li $s0, 3 # loop counter li $t4, 0x2 # Enable device interrupts sw $t4, 0($t0) sw $t4, 0($t2) mfc0 $t4, $12 # Enable interrupts and mask in Status reg ori $t4, $t4, 0xff01 mtc0 $t4, $12 l3: b l3 # Loop waiting for interrupts # Trap handler. Replaces the standard SPIM handler. .ktext 0x80000180 mfc0 $t4, $13 # Get ExcCode field from Cause reg srl $t5, $t4, 2 and $t5, $t5, 0x1f # ExcCode field bne $t5, 0, exception # An interrupt: and $t5, $t4, 0x800 # Check for IP3 (HW 1) beq $t5, 0, check_trans # Receiver interrupt: lw $t5, 0($t0) # Check receiver ready and $t5, $t5, 1 beq $t5, 0, no_recv_ready # Error if receiver is not ready lw $t6, 0($t1) # Read character li $t7, 1 beq $t6, 0xa, decr2 # New line (nl) bne $t6, 0xd, next # Carriage return (cr) decr2: add $s0, $s0, -1 # Decrement line counter next: mfc0 $t4, $13 # Get Cause register andi $t4, 0xfffff7ff # Clear IP3 bit mtc0 $t4, $13 check_trans: beq $t7, 0, ret_handler # No char to write yet and $t5, $t4, 0x400 # Check for IP2 (HW 0) beq $t5, 0, check_loop # Transmitter interrupt: lw $t5, 0($t2) # Check transmitter ready and $t5, $t5, 1 beq $t5, 0, no_trans_ready sw $t6, 0($t3) # Write character li $t7, 0 mfc0 $t4, $13 # Get Cause register andi $t4, 0xfffffbff # Clear IP2 bit mtc0 $t4, $13 check_loop: bne $s0, 0, ret_handler # If line counter not zero, get another line # Done echoing, so terminate program. li $v0, 10 syscall # syscall 10 (exit) # Return from handler. ret_handler: mfc0 $t4, $12 # Enable interrupts and mask in Status reg ori $t4, $t4, 0xff01 mtc0 $t4, $12 eret # return to interrupted instruction exception: li $v0, 4 # Non-interrupt exception la $a0, other_str # Print message and ignore syscall b ret_handler no_recv_ready: li $v0, 4 # Receiver was not ready after interrupt la $a0, no_recv_str # Print message and ignore syscall b ret_handler bad_int: li $v0, 4 # Interrupt was not from recv or trans la $a0, bad_int_str # Print message and ignore syscall b ret_handler no_trans_ready: li $v0, 4 # Transmitter was not ready after interrupt la $a0, no_trans_str # Print message and ignore syscall b ret_handler .data

prompt: .asciiz' "Enter an equation "X+Y=" where X,Y are single digit integers. " other_str: .asciiz "Non-interrupt exception " no_recv_str: .asciiz "Receiver not ready " no_trans_str: .asciiz "Transmitter not ready " bad_int_str: .asciiz "Unknown interrupt "