用C8051F040做项目时，本来程序可以正常运行，添加一部分程序后发现无法进入main函数。断点调试发现，在文件STARTUP.A51中，跳转到
LJMP ?C_START 后，
又重新跳回
IDATALOOP: MOV @R0,A
DJNZ R0,IDATALOOP
ENDIF
想到之前遇到过类似问题，并在网上搜到了解决方法，如http://blog.sina.com.cn/s/blog_7732ffc90102wus1.html
上述方法说的是可能在初始化过程中发生了看门狗复位，于是我参照该文，并按照F040的使用手册，修改了文件STARTUP.A51，在进入main之前，关闭了看门狗，修改的如下（红色为添加的）：
$NOMOD51
;------------------------------------------------------------------------------
; 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.
;
; To translate this file use A51 with the following invocation:
;
; A51 STARTUP.A51
;
; To link the modified STARTUP.OBJ file to your application use the following
; Lx51 invocation:
;
; Lx51 your object file list, STARTUP.OBJ controls
;
;------------------------------------------------------------------------------
;
; User-defined <h> Power-On Initialization of Memory
;
; With the following EQU statements the initialization of memory
; at processor reset can be defined:
;
; <o> IDATALEN: IDATA memory size <0x0-0x100>
; <i> Note: The absolute start-address of IDATA memory is always 0
; <i> The IDATA space overlaps physically the DATA and BIT areas.
IDATALEN EQU 80H
;
; <o> XDATASTART: XDATA memory start address <0x0-0xFFFF>
; <i> The absolute start address of XDATA memory
XDATASTART EQU 0
;
; <o> XDATALEN: XDATA memory size <0x0-0xFFFF>
; <i> The length of XDATA memory in bytes.
XDATALEN EQU 0
;
; <o> PDATASTART: PDATA memory start address <0x0-0xFFFF>
; <i> The absolute start address of PDATA memory
PDATASTART EQU 0H
;
; <o> PDATALEN: PDATA memory size <0x0-0xFF>
; <i> The length of PDATA memory in bytes.
PDATALEN EQU 0H
;
;</h>
;------------------------------------------------------------------------------
;
;<h> Reentrant Stack Initialization
;
; The following EQU statements define the stack pointer for reentrant
; functions and initialized it:
;
; <h> Stack Space for reentrant functions in the SMALL model.
; <q> IBPSTACK: Enable SMALL model reentrant stack
; <i> Stack space for reentrant functions in the SMALL model.
IBPSTACK EQU 0 ; set to 1 if small reentrant is used.
; <o> IBPSTACKTOP: End address of SMALL model stack <0x0-0xFF>
; <i> Set the top of the stack to the highest location.
IBPSTACKTOP EQU 0xFF +1 ; default 0FFH+1
; </h>
;
; <h> Stack Space for reentrant functions in the LARGE model.
; <q> XBPSTACK: Enable LARGE model reentrant stack
; <i> Stack space for reentrant functions in the LARGE model.
XBPSTACK EQU 0 ; set to 1 if large reentrant is used.
; <o> XBPSTACKTOP: End address of LARGE model stack <0x0-0xFFFF>
; <i> Set the top of the stack to the highest location.
XBPSTACKTOP EQU 0xFFFF +1 ; default 0FFFFH+1
; </h>
;
; <h> Stack Space for reentrant functions in the COMPACT model.
; <q> PBPSTACK: Enable COMPACT model reentrant stack
; <i> Stack space for reentrant functions in the COMPACT model.
PBPSTACK EQU 0 ; set to 1 if compact reentrant is used.
;
; <o> PBPSTACKTOP: End address of COMPACT model stack <0x0-0xFFFF>
; <i> Set the top of the stack to the highest location.
PBPSTACKTOP EQU 0xFF +1 ; default 0FFH+1
; </h>
;</h>
;------------------------------------------------------------------------------
;
; Memory Page for Using the Compact Model with 64 KByte xdata RAM
; <e>Compact Model Page Definition
;
; <i>Define the XDATA page used for PDATA variables.
; <i>PPAGE must conform with the PPAGE set in the linker invocation.
;
; Enable pdata memory page initalization
PPAGEENABLE EQU 0 ; set to 1 if pdata object are used.
;
; <o> PPAGE number <0x0-0xFF>
; <i> uppermost 256-byte address of the page used for PDATA variables.
PPAGE EQU 0
;
; <o> SFR address which supplies uppermost address byte <0x0-0xFF>
; <i> most 8051 variants use P2 as uppermost address byte
PPAGE_SFR DATA 0A0H
;
; </e>
;------------------------------------------------------------------------------
; Standard SFR Symbols
ACC DATA 0E0H
B DATA 0F0H
SP DATA 81H
DPL DATA 82H
DPH DATA 83H
WDTCN DATA 0FFH;看门狗控制寄存器地址
NAME ?C_STARTUP
?C_C51STARTUP SEGMENT CODE
?STACK SEGMENT IDATA
RSEG ?STACK
DS 1
EXTRN CODE (?C_START)
PUBLIC ?C_STARTUP
CSEG AT 0
?C_STARTUP: LJMP STARTUP1
RSEG ?C_C51STARTUP
STARTUP1:
MOV WDTCN,#0DEh ; 禁止软件看门狗定时器
MOV WDTCN, #0ADh
IF IDATALEN <> 0
MOV R0,#IDATALEN - 1
CLR A
IDATALOOP: MOV @R0,A
DJNZ R0,IDATALOOP
ENDIF
IF XDATALEN <> 0
MOV DPTR,#XDATASTART
MOV R7,#LOW (XDATALEN)
IF (LOW (XDATALEN)) <> 0
MOV R6,#(HIGH (XDATALEN)) +1
ELSE
MOV R6,#HIGH (XDATALEN)
ENDIF
CLR A
XDATALOOP: MOVX @DPTR,A
INC DPTR
DJNZ R7,XDATALOOP
DJNZ R6,XDATALOOP
ENDIF
IF PPAGEENABLE <> 0
MOV PPAGE_SFR,#PPAGE
ENDIF
IF PDATALEN <> 0
MOV R0,#LOW (PDATASTART)
MOV R7,#LOW (PDATALEN)
CLR A
PDATALOOP: MOVX @R0,A
INC R0
DJNZ R7,PDATALOOP
ENDIF
IF IBPSTACK <> 0
EXTRN DATA (?C_IBP)
MOV ?C_IBP,#LOW IBPSTACKTOP
ENDIF
IF XBPSTACK <> 0
EXTRN DATA (?C_XBP)
MOV ?C_XBP,#HIGH XBPSTACKTOP
MOV ?C_XBP+1,#LOW XBPSTACKTOP
ENDIF
IF PBPSTACK <> 0
EXTRN DATA (?C_PBP)
MOV ?C_PBP,#LOW PBPSTACKTOP
ENDIF
MOV SP,#?STACK-1
; This code is required if you use L51_BANK.A51 with Banking Mode 4
;<h> Code Banking
; <q> Select Bank 0 for L51_BANK.A51 Mode 4
#if 0
; <i> 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
;</h>
LJMP ?C_START
END
但是问题依然没有解决。当时以为是添加的两句话语法不对，于是补了下汇编的知识，把这两句话来回改变位置，或者改用其他指令实现关闭看门狗，依然无效。
想到程序中用到了大量数组，想着可能是数组操作发生越界之类的问题。于是，便把程序中的代码一部分一部分的注释掉，直到把所有的程序全注释掉（只留空的main函数），问题依然存在。
不会是头文件的问题吧？便把main中include的所有自己写的.h注释掉，问题解决了。再逐个注释掉，发现自己写的sts_sys.h有问题。仔细检查后，发现该头文件中一开始写了
#ifndef __STS_SYS_H
#define __STS_SYS_H
但最后没写#endif，加上这句话就好了！！！问题解决！
涨姿势了，可是尚且不知道原理。