4. 7 汇编与 C 言语彼此调用试验
4. 7. 1 试验意图
阅览S3C2410 发动代码，调查处理器发动进程；
学会运用 MDK 集成开发环境辅佐窗口来分析判断调试进程和成果；
学会在 MDK 集成开发环境中编写、编译与调试汇编和C 言语彼此调用的程序。
4. 7. 6 试验参阅程序
1.randtest.c 参阅源代码：
/*********************************************************************************************
* File： randtest.c
* Author: Wuhan R&D Center, embest
* Desc： Random number generator demo program
* Calls assembler function randomnumber defined in random.s
* History:
*********************************************************************************************/
/*——————————————————————————————*/
/* extern function */
/*——————————————————————————————*/
extern unsigned int randomnumber( void );
unsigned int unRandom[10];
/*********************************************************************************************
* name: main
* func: c code entry
* para: none
* ret: none
* modify:
* comment:
*********************************************************************************************/
int __main()
{
unsigned int i,nTemp;
for( i = 0; i < 10; i++ )
{
nTemp = randomnumber();
unRandom[i] = nTemp;
}
while(1);
}
2.random.s 参阅源代码：
;#************************************************************************************************************
;# File： random.s *
;# Author: Wuhan R&D Center, embest *
;# Desc： Random number generator *
;# This uses a 33-bit feedback shift register to generate a pseudo-randomly *
;# ordered sequence of numbers which repeats in a cycle of length 2^33 – 1 *
;# NOTE: randomseed should not be set to 0, otherwise a zero will be generated *
;# continuously (not particularly random!). *
;# This is a good application of direct ARM assembler, because the 33-bit *
;# shift register can be implemented using RRX (which uses reg + carry). *
;# An ANSI C version would be less efficient as the compiler would not use RRX. *
;# AREA |Random$$code|, CODE, READONLY *
;# History: *
;#*************************************************************************************************************
;/*——————————————————————————————*/
;/* global symbol define */
;/*——————————————————————————————*/
global randomnumber
global seed
;/*——————————————————————————————*/
;/* code */
;/*——————————————————————————————*/
AREA BLOCK, code , readonly
EXPORT randomnumber
randomnumber
;# on exit:
;# a1 = low 32-bits of pseudo-random number
;# a2 = high bit (if you want to know it)
ldr ip, seedpointer
根据S3C2410 嵌入式 MDK 开发试验与实践――EduKit 系列丛书
Email：support@edukit.com.cn Tel：0755-25631365
ldmia ip, {a1, a2}
tst a2, a2, lsr #1 ;/* to bit into carry */
movs a3, a1, rrx ;/* 33-bit rotate right */
adc a2, a2, a2 ;/* carry into LSB of a2 */
eor a3, a3, a1, lsl #12 ;/* (involved!) */
eor a1, a3, a3, lsr #20 ;/* (similarly involved!) */
stmia ip, {a1, a2}
BX lr
seedpointer
DCD seed
seed
DCD 0x55555555
DCD 0x55555555
END
