Assembly - Prime/Not Prime - LC3

Question

I would like to know, why this code gives an error: invalid TRAP executed. Isn't the code correct? The input of a decimal is registered in R0 and if the number is prime, R0 will contain 1 at the end of the program and if the input_value is not prime, R0 will contain 0.

.ORIG x3000

    LD R0, INPUT_NUMBER       ; Load the input number directly into R0
    AND R2, R0, #0            ; Clear R2 to use for comparisons
    ADD R2, R0, #-1           ; Adjust for checking if input is 0 or 1
    BRz IS_NOT_PRIME          ; If input is 0, it's not prime
    BRn CONTINUE_CHECK        ; If input is negative, skip to array check (not possible in this context, but good practice)
    ADD R2, R2, #1            ; Adjust R2 back for normal processing

CONTINUE_CHECK:
    LEA R3, PRIME_ARRAY       ; Load the address of the prime array into R3
    ADD R3, R3, R0            ; Calculate the address to check in the array (using R0's value directly)
    LDR R4, R3, #0            ; Load the value at that index into R4
    BRz IS_NOT_PRIME          ; If the value is 0, it's not prime

    ; If the value is 1, it's prime
    LD R0, PRIME_VAL          ; Set R0 to 1 to indicate prime
    LEA R1, PRIME_MSG         ; Load address of prime message into R1
    PUTS                      ; Print the prime message
    BR FINISH                 ; We are done

IS_NOT_PRIME:
    AND R0, R0, #0            ; Set R0 to 0 to indicate not prime
    LEA R1, NOT_PRIME_MSG     ; Load address of not prime message into R1
    PUTS                      ; Print the not prime message

FINISH:
    HALT                      ; Stop the program

; Data section
INPUT_NUMBER  .FILL #3            ; Test value (change this to the number to test)
PRIME_VAL     .FILL #1            ; Value to indicate prime
NOT_PRIME_MSG .STRINGZ "0\n"      ; Message for not prime number
PRIME_MSG     .STRINGZ "1\n"      ; Message for prime number
PRIME_ARRAY   .FILL #0            ; 0 is not prime
                .FILL #0            ; 1 is not prime
                .FILL #1            ; 2 is prime
                .FILL #1            ; 3 is prime
                .FILL #0            ; 4 is not prime
                .FILL #1            ; 5 is prime
                ; Continue for numbers 6-99 if needed

.END

I tested the code in WebLC3 Simulator, and it gives an error, invalid TRAP executed.

Answer 1

You have incorrect usage of PUTS. FYI, PUTS is shorthand TRAP #22.

PUTS requires the address of null-character terminated string to print goes in R0, and that's the only register used to pass parameter to puts.  (By passing 0 or 1 to PUTS (i.e. in R0) as you're doing now, it will fail in some manner.)

Since R0 is necessarily used/repurposed to pass a parameter (address of string to print) to PUTS, then if the intent is to leave the program (at HALT) with R0 as holding 0 or 1 (depending on the prime result), you will then obviously need to set R0 after the PUTS trap.