$.$text

$.$globl init$\_$interrupts, isr$\_$handler, isr$\_$done

init$\_$interrupts:

addi sp$,$ sp$,-8$

sw ra$,0($sp$)$

# Print "Initializing Interrupts" message

la a$0,$ init$\_$msg # Load the message address

jal printString # Call the printString subroutine

# Enable Receiver Interrupt

li t$0,0$x$1$ # Set enable bit

lui t$1,0$xFFFF$0$ # Load base address of RCR

sw t$0,4($t$1)$ # Write to RCR to enable interrupts

# Enable global interrupts

csrsi mstatus, $0$x$8$ # Set MIE bit in mstatus

csrsi mie, $0$x$800$ # Enable external interrupts in mie

lw ra$,0($sp$)$

addi sp$,$ sp$,8$

ret

isr$\_$handler:

addi sp$,$ sp$,-16$ # Allocate stack space

sw ra$,0($sp$)$ # Save return address

sw s$0,4($sp$)$ # Save callee$-$saved register s$0$

# Step $1$: Check the Ready Bit

lui t$0,0$xFFFF$0$ # Load base address of RCR

lw t$1,0($t$0)$ # Read Receiver Control Register $($RCR$)$

andi t$2,$ t$1,0$x$1$ # Check Ready Bit $($bit $0)$

beqz t$2,$ isr$\_$done # Exit if no key is ready

# Step $2$: Read the Key Pressed

lw t$3,0($t$0)$ # Load the key from Receiver Data Register $($RDR$)$

mv a$0,$ t$3$ # Move key to a$0$ for printing

# Step $3$: Print the Key Pressed

la a$1,$ key$\_$msg # Load "Key Pressed is: $"$ message

jal printString # Print the message

jal printChar # Print the key $($a$0$ contains the key$)$

# Step $4$: Increment Persistent Counter

la s$0,$ int$\_$count # Load address of counter in memory

lw t$4,0($s$0)$ # Load current counter value

addi t$4,$ t$4,1$ # Increment counter by $1$

sw t$4,0($s$0)$ # Store updated counter back to memory

# Step $5$: Restart Main After $5$ Key Presses

li t$5,5$ # Compare counter with $5$

bne t$4,$ t$5,$ isr$\_$done # Skip if not equal to $5$

sw zero, $0($s$0)$ # Reset counter to $0$

la t$6,$ main$\_$start # Load the start address of main

csrw mepc, t$6$ # Modify return address to restart main

isr$\_$done:

lw s$0,4($sp$)$ # Restore callee$-$saved register

lw ra$,0($sp$)$ # Restore return address

addi sp$,$ sp$,16$ # Deallocate stack space

uret # Return from interrupt

$.$data

KBSR: $.$word $0$xFFFF$0000$

RDR: $.$word $0$xFFFF$0004$

key$\_$msg: $.$string $"$

Key Pressed is: $"$

init$\_$msg: $.$string $"$

Initializing Interrupts

$"$

newline: $.$string $"$

$"$

last$\_$key: $.$word $0$ # Persistent storage for last key Error in D:$\backslash 225-$Agn$7\mathrm{.}2\backslash$isr$.$asm line $18$ column $11$: "mstatus": operand is of incorrect type

Error in D:$\backslash 225-$Agn$7\mathrm{.}2\backslash$isr$.$asm line $19$ column $11$: "mie": operand is of incorrect type

Error in D:$\backslash 225-$Agn$7\mathrm{.}2\backslash$isr$.$asm line $56$ column $10$: "mepc": operand is of incorrect type

Assemble: operation completed with errors. I get these errors using rars $1\mathrm{.}6.$ Example Output

Below is the output of the fully functional program.

Initializing Interrupts

$**********$

Key Pressed is: $1$

$11111111111111111111111111111111111111$

Key Pressed is: $2$

$22222222222222222222222$

Key Pressed is: $3$

$3333333333333$

Key Pressed is: $4$

$44444444444444444444444$

Key Pressed is: $5$

Initializing Interrupts

$********************$