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        Startup code 啟動文件c51

        作者:hkxiaoma   來源:互聯網   點擊數:  更新時間:2014年07月29日   【字體:

        Startup code:啟動代碼。在Keil中,啟動代碼在復位目標系統后立即被執行。啟動代碼主要實現以下功能:

        (1)       清除內部數據存儲器
        (2)       清除外部數據存儲器
        (3)       清除外部頁存儲器
        (4)       初始化small模式下的可重入棧和指針
        (5)       初始化large模式下的可重入棧和指針
        (6)       初始化compact模式下的可重入棧和指針
        (7)       初始化8051硬件棧指針
        (8)       傳遞初始化全局變量的控制命令或者在沒有初始化全局變量時給main函數傳遞命令。
        在每一個啟動文件中,提供了可供用戶自己修改有來控制程序執行的匯編常量。見表1
        表1
        Name
        Description
        IDATALEN
        Specifies the number of bytes of idata to clear to 0. The default is 80h because most 8051 derivatives contain at least 128 bytes of internal data memory. Use a value of 100h for the 8052 and other derivatives that have 256 bytes of internal data memory.
        XDATASTART
        Specifies the initial xdata address to clear to 0.
        XDATALEN
        Indicates the number of bytes of xdata to clear to 0. The default is 0.
        PDATASTART
        Specifies the initial pdata address to clear to 0.
        PDATALEN
        Specifies the number of bytes of pdata to clear to 0. The default is 0.
        IBPSTACK
        Specifies whether or not the small model reentrant stack pointer (?C_IBP) should be initialized. A value of 1 causes this pointer to be initialized. A value of 0 prevents initialization of this pointer. The default is 0.
        IBPSTACKTOP
        Specifies the top of the small model reentrant stack. The default is 0xFF in idata memory.
        The Cx51 Compiler does not check to see if the stack area available satisfies the requirements of the application. It is your responsibility to perform such a test.
        XBPSTACK
        Specifies whether or not the large model reentrant stack pointer (?C_XBP) should be initialized. A value of 1 causes this pointer to be initialized. A value of 0 prevents initialization of this pointer. The default is 0.
        XBPSTACKTOP
        Specifies the top of the large model reentrant stack. The default is 0xFFFF in xdata memory.
        The Cx51 Compiler does not check to see if the stack area available satisfies the requirements of the application. It is your responsibility to perform such a test.
        PBPSTACK
        Specifies whether the compact model reentrant stack pointer (?C_PBP) should be initialized. A value of 1 causes this pointer to be initialized. A value of 0 prevents initialization of this pointer. The default is 0.
        PBPSTACKTOP
        Specifies the top of the compact model reentrant stack. The default is 0xFF in pdata memory.
        The Cx51 Compiler does not check to see if the stack area available satisfies the requirements of the application. It is your responsibility to perform such a test.
        PPAGEENABLE
        Enables (a value of 1) or disables (a value of 0) Port 2 initialization for pdata memory access. The default is 0. pdata addressing uses Port 2 for the upper address (or page) byte.
        PPAGE
        Specifies the value to write to Port 2 of the 8051 for pdata memory access. This value represents the xdata memory page to use for pdata. This is the upper 8 bits of the absolute address range to use for pdata. For example, if the pdata area begins at address 1000h (page 10h) in xdata memory, PPAGEENABLE should be set to 1, and PPAGE should be set to 10h. You must specify the starting pdata address to use to the BL51 Linker using the PDATA directive. For example:
        BL51 input modules PDATA (1050H)
        
        Neither the BL51 Linker nor the Cx51 Compiler checks to see if the PDATA directive and the PPAGE startup constant are correctly specified. You must ensure that these parameters contain suitable values.
        上面這些只是標號,如果愿意,自己可以換成其他的名字。這樣寫意義更直觀。
          
        $NOMOD51
        ;不使用預先定義的SFR,The NOMOD51 directive suppresses pre-definition of 8051 SFR
        ;names. This directive must be used when a customer-specific SFR definition file is included.
        ;------------------------------------------------------------------------------
         This file is part of the C51 Compiler package
         Copyright (c) 1988-2005 Keil Elektronik GmbH and Keil Software, Inc.
         Version 8.01
        ;
         *** <<< Use Configuration Wizard in Context Menu >>> ***
        ;------------------------------------------------------------------------------
         STARTUP.A51:  This code is executed after processor reset.
        ;代碼在處理器復位后執行
         To translate this file use A51 with the following invocation:
        ;通過A51用下面的命令傳遞該文件
            A51 STARTUP.A51
        ;
         To link the modified STARTUP.OBJ file to your application use the following
         Lx51 invocation:
        ;利用下面Lx51命令來鏈接修改的STARTUP.OBJ文件到實際的應用
            Lx51 your object file list, STARTUP.OBJ  controls
        ;
        ;------------------------------------------------------------------------------
        ;
         User-defined Power-On Initialization of Memory
        ;用戶自定義上電初始化內存
         With the following EQU statements the initialization of memory
         at processor reset can be defined:
        ;在處理器復位時通過EQU來初始化內存
        ; IDATALEN: IDATA memory size <0x0-0x100>
        ;IDATALEN:IDATA存儲區的大小<0-256>,可以根據自己的選擇修改
            Note: The absolute start-address of IDATA memory is always 0
                   The IDATA space overlaps physically the DATA and BIT areas.
        ;IDATA絕對的起始地址總是0
        ;IDATA空間涵蓋物理上的DATA和BIT區
        ;需用0來初始化idata區的字節數
        IDATALEN        EQU     80H
        ;
        ; XDATASTART: XDATA memory start address <0x0-0xFFFF>
            The absolute start address of XDATA memory
        ;XDATA存儲區的起始地址,XDATA內存的絕對起始地址。
        XDATASTART      EQU     0    
        ;指定初始的XDATA地址清0
        ; XDATALEN: XDATA memory size <0x0-0xFFFF>
            The length of XDATA memory in bytes.
        ;XDATA空間的長度,以字節為單位
        XDATALEN        EQU     0     
        ;說明xdata的字節數清0,該值默認為0
        ; PDATASTART: PDATA memory start address <0x0-0xFFFF>
            The absolute start address of PDATA memory
        PDATASTART      EQU     0H
        ;
        ; PDATALEN: PDATA memory size <0x0-0xFF>
            The length of PDATA memory in bytes.
        PDATALEN        EQU     0H
        ;
        ;
        ;------------------------------------------------------------------------------
        ;
        ; Reentrant Stack Initialization
        ;重入棧的初始化
         The following EQU statements define the stack pointer for reentrant
         functions and initialized it:
        ;EQU語句定義了重入函數的棧指針并初始化
        ; Stack Space for reentrant functions in the SMALL model.
        ;SMALL模式下的重入函數棧
         IBPSTACK: Enable SMALL model reentrant stack
        ; IBPSTACK = 1使能模擬棧
            Stack space for reentrant functions in the SMALL model.
        IBPSTACK        EQU     0       ; set to 1 if small reentrant is used.
         IBPSTACKTOP: End address of SMALL model stack <0x0-0xFF>
        ; IBPSTACKTOP:棧的結束地址<0x0-0xFF>
            Set the top of the stack to the highest location.
        ;設置為最高地址(向下生長的)
        ;默認FFH+1(其實就是0,使用時進行操作(+0xFF)使其變為0xFF)
        IBPSTACKTOP     EQU     0xFF +1     ; default 0FFH+1  
        ;
        ;下面是LARGE模式下的模擬棧,和SMALL相同不做特別說明
        ; Stack Space for reentrant functions in the LARGE model.     
         XBPSTACK: Enable LARGE model reentrant stack
            Stack space for reentrant functions in the LARGE model.
        XBPSTACK        EQU     0       ; set to 1 if large reentrant is used.
         XBPSTACKTOP: End address of LARGE model stack <0x0-0xFFFF>
            Set the top of the stack to the highest location.
        XBPSTACKTOP     EQU     0xFFFF +1   ; default 0FFFFH+1
        ;
        ;COMPACT模式下
        ; Stack Space for reentrant functions in the COMPACT model.   
         PBPSTACK: Enable COMPACT model reentrant stack
            Stack space for reentrant functions in the COMPACT model.
        PBPSTACK        EQU     0       ; set to 1 if compact reentrant is used.
        ;
          PBPSTACKTOP: End address of COMPACT model stack <0x0-0xFFFF>
            Set the top of the stack to the highest location.
        PBPSTACKTOP     EQU     0xFF +1     ; default 0FFH+1  
        ;
        ;
        ;------------------------------------------------------------------------------
        ;COMPACT模式下64K xdata的頁存儲器
         Memory Page for Using the Compact Model with 64 KByte xdata RAM
         Compact Model Page Definition
        ;通過PDATA變量定義XDATA頁
         Define the XDATA page used for PDATA variables.
         PPAGE must conform with the PPAGE set in the linker invocation.
        ;PPAGE必須與鏈接器引用設置一致
        ; Enable pdata memory page initalization
        PPAGEENABLE     EQU     0       ; set to 1 if pdata object are used.
        ;設置1使能
        ; PPAGE number <0x0-0xFF>
        uppermost 256-byte address of the page used for PDATA variables.
        ;頁號,PDATA變量高256字節地址(高8位地址)
         PPAGE           EQU     0
        ;
        ; SFR address which supplies uppermost address byte <0x0-0xFF>
        most 8051 variants use P2 as uppermost address byte
        ;提供高字節地址的SFR的地址(高8位地址的存放位置),一般的8051單片機用P2口
        PPAGE_SFR       DATA    0A0H
        ;
        ;
        ;------------------------------------------------------------------------------
         
        ; Standard SFR Symbols
        ;使用偽指令DATA為寄存器分配地址或者為響應的地址起一個別名
        ACC     DATA    0E0H
              DATA    0F0H
        SP      DATA    81H
        DPL     DATA    82H
        DPH     DATA    83H
         
                        NAME    ?C_STARTUP    ;定義當前模塊的目標模塊名
        ;NAME:
        ; NAME (modulename)
        ;NAME為輸出文件定義一個模塊名稱(modulename),如果在文件中沒有特定的
        ; (modulename),默認的應用第一個輸入文件的名稱。
         
        ?C_C51STARTUP   SEGMENT   CODE
        ;定義一個代碼段,名稱?C_C51STARTUP
        ?STACK          SEGMENT   IDATA                     ;堆棧
                        RSEG    ?STACK                                 ;RSEG選擇一個先前聲明的可重定位的段
                        DS      1                                                 ;為堆棧預留一個低階的存儲空間
                        EXTRN CODE (?C_START)               ;當前源文件中用的代碼段存儲區的符號?C_START,在其他的目標模塊中定義
                        PUBLIC  ?C_STARTUP                      ;聲明可以用于其他目標模塊的全局符號?C_STARTUP,用于和C相連接在.src文件中可以看到這個符號
                        CSEG    AT      0                                   ;選擇代碼存儲區內的一個絕對段,匯編從上面命令中的地址0開始執行這個段。
        ?C_STARTUP:     LJMP    STARTUP1            ;芯片上電復位后,執行的第一句就是該句,該句往下是開始執行啟動代碼
                        RSEG    ?C_C51STARTUP               ;選擇代碼段?C_C51STARTUP
         
        STARTUP1:     IF IDATALEN <> 0                                              ;如果IDATALEN不為0,則將長度-1送R0
                        MOV     R0,#IDATALEN - 1
                        CLR     A
        IDATALOOP:      MOV     @R0,A                                             ;將IDATA區清0
                        DJNZ    R0,IDATALOOP
        ENDIF
         
        IF XDATALEN <> 0            ;如果有外部數據存儲區
                        MOV     DPTR,#XDATASTART     ;起始地址送DPTR
                        MOV     R7,#LOW (XDATALEN)  ;長度低8為送R7
          IF (LOW (XDATALEN)) <> 0                                    ;低8位不為0
                        MOV     R6,#(HIGH (XDATALEN)) +1 ;高8位+1送R6,下面清0用
          ELSE
                        MOV     R6,#HIGH (XDATALEN)
          ENDIF
                        CLR     A                                      ;清0
        XDATALOOP:      MOVX    @DPTR,A
                        INC     DPTR
                        DJNZ    R7,XDATALOOP
                        DJNZ    R6,XDATALOOP
        ENDIF
         
        IF PPAGEENABLE <> 0                                                ;使能外部頁編址
                        MOV     PPAGE_SFR,#PPAGE       ;頁號送SFR
        ENDIF
         
        IF PDATALEN <> 0                                         ;0-FF之間
                        MOV     R0,#LOW (PDATASTART)
                        MOV     R7,#LOW (PDATALEN)
                        CLR     A
        PDATALOOP:      MOVX    @R0,A                       ;清0
                        INC     R0
                        DJNZ    R7,PDATALOOP
        ENDIF
         
        IF IBPSTACK <> 0                           ;使能SMALL模式下的模擬棧
        EXTRN DATA (?C_IBP)                    ;使用其他目標模塊中定義的?C_IBP(模擬棧指針)
                                                                ;(.M51文件中)
         
                        MOV     ?C_IBP,#LOW IBPSTACKTOP      ;模擬棧指針指向棧頂
        ENDIF
         
        IF XBPSTACK <> 0                                 ;Large模式下使能模擬棧
        EXTRN DATA (?C_XBP)
                                                                                            ;棧指針指向棧頂
                        MOV     ?C_XBP,#HIGH XBPSTACKTOP
                        MOV     ?C_XBP+1,#LOW XBPSTACKTOP
        ENDIF
         
        IF PBPSTACK <> 0                                                ;COMPACT模式下的模擬棧
        EXTRN DATA (?C_PBP)
                        MOV     ?C_PBP,#LOW PBPSTACKTOP     ;指向棧頂
        ENDIF
         
                        MOV     SP,#?STACK-1                               ;硬件棧SP賦值
        ;硬件棧與模擬棧相區別,硬件棧是向上的,模擬棧是向下的
        ;在M51中可以看到具體的?STACK的值
        ;模擬棧的指針指向所在模式下,存儲區最大地址+1(0xFF+1或0xFFFF+1)
        ;硬件棧初始化指向棧底-1;
        ;因為C51中棧操作是先操作棧指針(加或減),然后在寫數
        ; This code is required if you use L51_BANK.A51 with Banking Mode 4
        ; Code Banking
        Select Bank 0 for L51_BANK.A51 Mode 4
        #if 0  
            Initialize bank mechanism to code bank 0 when using L51_BANK.A51 with Banking Mode 4.
        EXTRN CODE (?B_SWITCH0)
                        CALL    ?B_SWITCH0      ; init bank mechanism to code bank 0
        #endif
        ;
                        LJMP    ?C_START                 ;執行main函數
         
                        END
        ;該文件中的一些符號的值的大小,可以在M51中看到,此外,可以通過系統上電復位后反
        ;匯編程序看到詳細的執行過程
        ;文件中的一些命令可以查閱KeilC幫助文檔
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