6510使用CBM Studio的程序集-带有分支错误的页面边界

Question

当我运行我的程序时，我得到了错误页的边界。在用于Windows10帮助的CBM prg studio应用程序中，没有任何地方解释我如何增加这个边界，或者我需要做些什么来避免这些错误。

它发生在基于标签E1cycle和E2cycle内的第110行和127行的相同指令上...

**Line 110:** BEQ space2reset     ; branch/jump if the result in A is 0

**Line 127:** BEQ space2reset     ; branch/jump if the result in A is 0

The errors...
**Line 110**:Page boundary crossed.   -   F:\C64\UltimateTests\test.asm

**Line 127**:Page boundary crossed.   -   F:\C64\UltimateTests\test.asm

[Error] Line 72:Invalid branch (200 bytes) "BEQ Name2    ; if we find it we branch using BEQ to name2 for msg2 "

[Error] Line 143:Invalid branch (-275 bytes) "BEQ StartBlackOut"

此外，正如您在上面看到的，我收到了这些奇怪的(200字节)和(-275字节)的无效分支错误--这是代码的一部分……

getnameb
        jsr $FF9F   ;SCNKEY, place ASCII character into keyboard queue
        jsr $FFE4   ;GETIN, this places the ASCII value into the Accumulator 

        BEQ getnameb ;loop until keys are pressed. (Branch if equal to zero)
        
        JSR $FFD2    ; CHROUT, print it to the screen as it is being typed in.
        CMP #13      ; CMP looks for the carrige return
        BEQ Name2    ; if we find it we branch using BEQ to name2 for msg2 
        
        CMP #32         ; Looking for space bar. If true error 1 is returned
        BEQ ErrorInput1

        ldx $0900    ; load into x the value at $0900 - replace what was there from JSRs
        STA $0019,x  ; also store what is being typed in consecutively? 
        INX          ; X IS INCREASED BY 1.
        stx $0900    ; Store X back to $0900, avoid being molested by the above JSRs
                     ; The value at $0900 is the length of the string!
        
        LDA $0900        ; Load into A the current length of the string 
        CMP #08          ; Looking for max 8 chars. If true error 2 is returned
        BEQ ErrorInput2
        
        JMP getnameb     ; if we don't we loop! 


;PRINT ERRORS 1 OR 2

;-----1
ErrorInput1   
        LDX #00       ; load into the x registry zero


E1cycle  
        LDA E1msg,x    ; load into A the E1msg, the x sequence.
        CMP #00        ; compare memory and accumulator to the value 0?    
        BEQ space2reset     ; branch/jump if the result in A is 0
        STA 1424,x     ; where on the screen does E1msg start?
        INX            ; inc x to move the print along 1 space?
        
        JMP E1cycle    ; jump back to the beginning of cycle and do it all again.

E1msg   text 'ERROR: NO SPACES PERMITTED - SPACE TO RESET'
        byte 0
;-----2

ErrorInput2  
        LDX #00       ; load into the x registry zero


E2cycle  
        LDA E2msg,x    ; load into A the E1msg, the x sequence.
        CMP #00        ; compare memory and accumulator to the value 0?    
        BEQ space2reset     ; branch/jump if the result in A is 0
        STA 1424,x     ; where on the screen does E1msg start?
        INX            ; inc x to move the print along 1 space?
        
        JMP E2cycle    ; jump back to the beginning of cycle and do it all again.

E2msg   text 'ERROR: MAX 8 CHARACTERS PERMITTED - SPACE TO RESET'
        byte 0

space2reset    
        jsr $FF9F   ;SCNKEY, place ASCII character into keyboard queue
        jsr $FFE4   ;GETIN, this places the ASCII value into the Accumulator 

        BEQ space2reset ;loop until keys are pressed. (Branch if equal to zero)
        
        CMP #32
        BEQ StartBlackOut ; Go to the very beginning of the programming and reset the whole thing!       

我需要用非常简单的术语向我解释这一点，因为我还在学习，有时发现这个行话有点难以理解。谢谢!

Answer 1

每条指令占用一定数量的字节(请查看每条指令的引用以了解更多信息)。例如，LDA nnnn需要3个字节。因此，在使用相对分支的情况下(beq、bcs、bcc等)代替绝对跳转(jmp)，程序计数器(PC)只能在页面内跳转，即在-128到127字节的范围内(从128字节向后到127字节向前)。

要修复它，您可以更改以下内容：

beq longShot
   ... // more than 127 bytes of code here...
longShot

变成这样：

bne +
    jmp longShot
+
   ... // more than 127 bytes of code here...
longShot

值得一提的是，一些汇编编译器，例如64tass支持长分支。它会自动将相对分支编译为绝对分支，以防超出该范围。我不使用这个选项，因为我更喜欢自己控制它。

Answer 2

当我运行我的程序时，我得到了错误页边界。在用于Windows10帮助的CBM prg studio应用程序中，没有任何地方解释我如何增加这个边界，或者我需要做些什么来避免这些错误。

您不能增加边界，这是硬件限制。相反，您应该确保条件分支的目标(即，它跳转到的位置)离分支指令本身不太远。换句话说，分支指令不能跳转到太远的目的地。(太远意味着相隔128个左右字节或更多)。

解决这个问题的方法可能是重新排列代码，使目标更接近分支指令。但如果做不到这一点，您可以这样做：

    bne n
    jmp where_you_want_to_go
n:  ; label for the next instruction after the jump

而不是这个

    beq where_you_want_to_go