Write a LC-3 subroutine for printing “Hello” for N times. Write a main program to input N from the keyboard, call the subroutine and then output “Hello” for N times.

Sure, here's an example LC-3 subroutine and main program that accomplishes this task:

.ORIG x3000

; Subroutine to print "Hello" for N times
; Input: R1 = N
; Output: None

PRINT_HELLO  ST R7, SAVE_R7   ; Save R7 on the stack
             ADD R7, R7, #-2 ; Allocate space for local variable
             STR R1, R7, #0  ; Store N in local variable
             LD R0, HELLO    ; Load address of "Hello" string into R0
             AND R1, R1, #0  ; Clear R1
LOOP         BRz END_LOOP    ; Exit loop if R1 is 0
             PUTS            ; Print "Hello"
             ADD R1, R1, #-1 ; Decrement loop counter
             BR LOOP         ; Repeat loop
END_LOOP     LDR R1, R7, #0  ; Restore N from local variable
             ADD R7, R7, #2  ; Deallocate space for local variable
             LD R7, SAVE_R7  ; Restore R7 from the stack
             RET

HELLO        .STRINGZ "Hello\n"
SAVE_R7     .FILL x0000

; Main program to input N, call PRINT_HELLO, and output "Hello" for N times
; Input: None
; Output: None

MAIN         LEA R0, PROMPT   ; Prompt user for input
             PUTS
             GETC            ; Read first character of input
             OUT             ; Echo input back to the console
             AND R1, R1, #0  ; Clear R1
             ADD R0, R0, #-10 ; Convert ASCII character to decimal value
             ADD R1, R1, R0  ; Add decimal value to R1
GET_INPUT    GETC            ; Read next character of input
             BRz CALL_PRINT  ; Exit loop if user pressed Enter
             OUT             ; Echo input back to the console
             ADD R0, R0, #-10 ; Convert ASCII character to decimal value
             ADD R1, R1, R0  ; Add decimal value to R1
             BR GET_INPUT    ; Repeat loop
CALL_PRINT   JSR PRINT_HELLO ; Call PRINT_HELLO subroutine
             HALT

PROMPT       .STRINGZ "Enter a number: "

Here's a brief description of how the code works:

1. The `PRINT_HELLO` subroutine takes a single input parameter `R1`, which represents the number of times to print "Hello". It saves the value of `R7` onto the stack, allocates space for a local variable, and stores `N` in the local variable.
2. The subroutine then enters a loop that prints "Hello" using the `PUTS` instruction, decrements the loop counter (`R1`), and repeats the loop until `R1` is zero.
3. After the loop completes, the subroutine restores the value of `N` from the local variable, deallocates the space for the local variable, restores `R7` from the stack, and returns control to the calling program.
4. The `MAIN` program prompts the user to enter a number `N`, reads the input from the keyboard, and converts the ASCII characters to a decimal value stored in `R1`.
5. The `MAIN` program then calls the `PRINT_HELLO` subroutine with `N` as the input parameter, which prints "Hello" `N` times.
6. Finally, the program halts execution.

Note that this code assumes that the LC-3 has a `PUTS` instruction for printing strings to the console. If `PUTS` is not available, you'll need to write your own subroutine to print characters or strings.