你现在是一名大学生，请你以子程序的形式完善以子程序的形式改写assume cs:code data segment db 'welcome to masm!' db 2,36,113 data ends code segment start: mov ax,data mov ds,ax mov bx,0 mov di,16 mov ax,0b800h mov es,ax mov si,16012+352 mov cx,3 s: mov ah,ds:[di] push cx mov cx,16 s1: mov al,ds:[bx] mov es:[si],ax add si,2 inc bx loop s1 pop cx add si,128 inc di mov bx,0 loop s mov ax,4c00h int 21h code ends end start

Sure, here is the code rewritten as a subroutine with additional functionality that takes in a message string as a parameter:

data segment
    message db 100 dup(0) ; define a buffer to hold the message string
data ends

code segment
start:
    mov ax, data
    mov ds, ax
    
    lea si, message ; load the address of the message string
    call print_message  ; call the print_message subroutine, passing in the message string as a parameter
    
    mov ax, 4c00h
    int 21h

print_message:
    push ax
    push bx
    push cx
    push di
    push si
    push es
    
    mov bx, 0
    mov di, 16
    mov ax, 0b800h
    mov es, ax
    mov cx, 3

print_loop:
    mov ah, ds:[di]
    push cx
    mov cx, 16
    
print_char_loop:
    mov al, [si] ; get the next character from the message string
    cmp al, 0 ; check if we've reached the end of the string
    je done_printing
    mov es:[si * 2 + 16012 + 352], ax ; print the character to the screen
    add si, 1 ; move to the next character in the string
    add bx, 1 ; increment the column counter
    loop print_char_loop
    
    done_printing:
    pop cx
    add si, 128 - (bx * 2) ; move to the next row
    mov bx, 0 ; reset the column counter
    inc di ; move to the next row in the video memory
    loop print_loop
    
    pop es
    pop si
    pop di
    pop cx
    pop bx
    pop ax
    ret
code ends
end start

The `print_message` subroutine takes care of printing the message to the screen, while the `start` routine sets up the data segment, loads the address of the message string into `si`, calls the `print_message` subroutine, and then ends the program.

In addition, the `print_message` subroutine takes in a message string as a parameter and prints it to the screen, character by character. Once the end of the string is reached, the subroutine exits.