C51编程的一些概念
.A51代码片断,红色是经常可能需要修改的地方:
;------------------------------------------------------------------------------
; This file is part of the C51 Compiler package
; Copyright KEIL ELEKTRONIK GmbH 1990
;------------------------------------------------------------------------------
; 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
; L51 invocation:
;
; L51
;
;------------------------------------------------------------------------------
;
; User-defined Power-On Initialization of Memory
;
; With the following EQU statements the initialization of memory
; at processor reset can be defined:
;
; ; the absolute start-address of IDATA memory is always 0
IDATALEN EQU 80H ; the length of IDATA memory in bytes.
;
XDATASTART EQU 0H ; the absolute start-address of XDATA memory
XDATALEN EQU 0H ; the length of XDATA memory in bytes.
;
PDATASTART EQU 0H ; the absolute start-address of PDATA memory
PDATALEN EQU 0H ; the length of PDATA memory in bytes.
;
; Notes: The IDATA space overlaps physically the DATA and BIT areas of the
; 8051 CPU. At minimum the memory space occupied from the C51
; run-time routines must be set to zero.
;------------------------------------------------------------------------------
;
; Reentrant Stack Initilization
;
; The following EQU statements define the stack pointer for reentrant
; functions and initialized it:
;
; Stack Space for reentrant functions in the SMALL model.
IBPSTACK EQU 0 ; set to 1 if small reentrant is used.
IBPSTACKTOP EQU 0FFH+1 ; set top of stack to highest location+1.
;
; Stack Space for reentrant functions in the LARGE model.
XBPSTACK EQU 0 ; set to 1 if large reentrant is used.
XBPSTACKTOP EQU 0FFFFH+1; set top of stack to highest location+1.
;
; Stack Space for reentrant functions in the COMPACT model.
PBPSTACK EQU 0 ; set to 1 if compact reentrant is used.
PBPSTACKTOP EQU 0FFFFH+1; set top of stack to highest location+1.
;
;------------------------------------------------------------------------------
;
; Page Definition for Using the Compact Model with 64 KByte xdata RAM
;
; The following EQU statements define the xdata page used for pdata
; variables. The EQU PPAGE must conform with the PPAGE control used
; in the linker invocation.
;
PPAGEENABLE EQU 0 ; set to 1 if pdata object are used.
PPAGE EQU 0 ; define PPAGE number.
;
;------------------------------------------------------------------------------
3. 标准输入输出文件
putchar.c
putchar.c是一个低级字符输出子程,开发人员可修改后应用到自己的硬件系统上,例如向CLD或LEN输出字符。
缺省:putchar.c是向串口输出一个字符XON|XOFF是流控标志,换行符“\*n”自动转化为回车/换行“\r\n”。
getkey.c
getkey函数是一个低级字符输入子程,该程序可用到自己硬件系统,如矩阵键盘输入中,缺省时通过串口输入字符。 4. 其它文件
还包括对Watch-Dog有独特功能的INIT.A51函数以及对8×C751适用的函数,可参考源代码。
第四节 段名协定与程序优化
1. 段名协定(Segment Naming Conventions)
C51编译器生成的目标文件存放于许多段中,这些段是代码空间或数据空间的一些单元,一个段可以是可重定位的,也可以是绝对段,每一个可重定位的段都有一个类型和名字,C51段名有以下规定:
每个段名包括前缀与模块名两部分,前缀表示存储类型,模块名则是被编译的模块的名字,例如:
?CO?main1 :表示main1模块中的代码段中的常数部分
?PR?function1?module 表module模块中函数function1的可执行段,具体规定参阅手册。
2. 程序优化
C51编译器是一个具有优化功能的编译器,它共提供六级优化功能。确保生成目标代码的最高效率(代码最少,运行速度最快)。具体六级优化的内容可参考帮助。
在C51中提供以下编译控制
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