ARM 匯編與 C 語言相互調用實驗

4. 7. 1 實驗目的

閱讀S3C2410 啟動代碼，觀察處理器啟動過程；

學會使用 MDK 集成開發環境輔助窗口來分析判斷調試過程和結果；

學會在 MDK 集成開發環境中編寫、編譯與調試匯編和C 語言相互調用的程序。

4. 7. 6 實驗參考程序

1.randtest.c 參考源代碼：

/*********************************************************************************************
* 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 參考源代碼：

;#************************************************************************************************************
;# 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

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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