基于DOSBox的8086汇编Connect4游戏RTC计时器实现求助

Hey there! Let's tackle this RTC-based timer for your Connect4 8086 assembly project—super doable, even for a university assignment. Here's a step-by-step breakdown to get that 20-second timeout and random auto-drop working:

The Real-Time Clock (RTC) in DOS is accessed via two I/O ports:

• 0x70: RTC address register (select which RTC register to read/write)
• 0x71: RTC data register (holds the value of the selected register)

RTC stores time values in BCD format (e.g., 25 seconds is 0x25), so we need to convert that to binary for arithmetic operations. The seconds register is at address 0x00 in the RTC.

First, write a helper function to read and convert the current RTC seconds to binary:

; Reads current RTC seconds, returns AL as binary value
ReadRTCSeconds:
    mov al, 0x00        ; Select seconds register (0x00)
    out 0x70, al        ; Send register address to RTC
    in al, 0x71         ; Read BCD seconds value

    ; Convert BCD to binary
    mov ah, al
    and al, 0x0F        ; Isolate lower 4 bits (units place)
    shr ah, 4           ; Shift upper 4 bits to lower (tens place)
    mov cl, 10
    mul cl              ; Multiply tens by 10
    add al, ah          ; Add units to get binary seconds
    ret

Next, integrate the timer logic into your player turn loop. We'll track the start time, check for input periodically, and trigger a random drop if 20 seconds pass:

; Define variables in your data segment
start_sec db ?
current_tick dw ?
selected_col db ?

PlayerTurn:
    ; Record start time of the turn
    call ReadRTCSeconds
    mov [start_sec], al

InputLoop:
    ; Check for keyboard input (keep your existing input check here)
    mov ah, 0x01
    int 0x16            ; DOS keyboard status call
    jnz HandleInput     ; If key pressed, process player's move

    ; Check if 20 seconds have passed
    call ReadRTCSeconds
    mov bl, al
    sub bl, [start_sec]

    ; Handle cross-minute wrap-around (e.g., start at 55s, current is 5s)
    cmp bl, 0
    jge CheckTimeout
    add bl, 60          ; Add 60 to get correct elapsed time

CheckTimeout:
    cmp bl, 20
    jge TimeoutDrop     ; Trigger auto-drop if timeout

    ; Add a small delay to avoid hogging CPU (uses DOS system tick, 18.2Hz)
    mov ah, 0x00
    int 0x1A            ; Get system tick count (DX = tick)
    mov [current_tick], dx
DelayLoop:
    int 0x1A
    sub dx, [current_tick]
    cmp dx, 18          ; Wait ~1 second (18 ticks = ~1s)
    jb DelayLoop

    jmp InputLoop

HandleInput:
    ; Your existing input handling code here (get column, validate, drop piece)
    ; ...
    jmp NextPlayer

TimeoutDrop:
    ; Generate random column (0-6 for Connect4's 7 columns)
    mov ah, 0x00
    int 0x1A            ; Get system tick count (DX is random-ish)
    mov ax, dx
    mov bl, 7
    div bl               ; AH = remainder (0-6, perfect for column index)
    mov [selected_col], ah

    ; Call your existing drop piece function with selected_col
    call DropPiece
    ; Add feedback for the user (e.g., print "Timeout! Auto-dropping in column X")
    ; ...
    jmp NextPlayer

NextPlayer:
    ; Switch to other player logic here
    ; ...

• Cross-minute wrap-around: The code above checks if the elapsed seconds are negative (meaning we've rolled over to the next minute) and adds 60 to get the correct elapsed time.
• CPU usage: The delay loop using INT 0x1A ensures we don't spin the CPU non-stop—this is important for DOSBox performance.
• NMI Lock (Fallback): Some DOS environments require disabling Non-Maskable Interrupts when accessing RTC. If you run into read errors, modify the ReadRTCSeconds function to set bit 7 of the address:

  mov al, 0x80        ; 0x80 + 0x00 = select seconds register + disable NMI
  out 0x70, al
  

• Test the timeout by letting the timer run without input—verify it triggers the auto-drop after 20 seconds.
• Test cross-minute scenarios (e.g., start the turn at 50 seconds, wait 10 seconds to hit 0, then another 10 to reach 20 total elapsed).
• Validate the random column selection ensures pieces only drop into valid (non-full) columns—you might want to add a check in TimeoutDrop to re-generate if the column is full.

内容的提问来源于stack exchange，提问作者Skyflyer