基于Cortex-A8裸机，点亮LED灯程序分析

main.c

#include "s5pc100.h"

void delay(int ms)
{
	int i;
	while (ms--) {
		i = 4000;
		while (i--);
	}
}


int main()
{
	int num = 0;
	char c;

	GPG3.GPG3CON = 0x1111;//将GPG3端口与LED相连的引脚设置为输出模式
	GPG3.GPG3DAT = 0;//数据寄存器的值设置为零

	while (1) {
		GPG3.GPG3DAT |= (1 << num);
		delay(500);
		GPG3.GPG3DAT &= ~(1 << num);
		delay(500);
		num++;
		num %= 4;
	}

	return 0;
}

		.text
		.global _start
_start:
		b	reset
		ldr	pc, _undefined_instruction
		ldr	pc, _software_interrupt
		ldr	pc, _prefetch_abort
		ldr	pc, _data_abort
		ldr	pc, _not_used
		ldr	pc, _irq
		ldr	pc, _fiq  

_undefined_instruction:
		.word  _undefined_instruction
_software_interrupt:
		.word  _software_interrupt
_prefetch_abort:
		.word  _prefetch_abort
_data_abort:
		.word  _data_abort
_not_used:
		.word  _not_used
_irq:
		.word  irq_handler
_fiq:
		.word  _fiq
  
reset:
		ldr	r0, =0x20008000
		mcr	p15, 0, r0, c12, c0, 0  /*将中断向量表的地址设置为从0x20008000开始*/
init_stack:
		ldr	r0, stackpointer	/* get stack pointer */
		mov	sp, r0
		sub	r0, #128 * 4		/* 512 byte  for irq mode of stack */
		msr	cpsr, #0xD2
		mov	sp, r0
		sub	r0, #128 * 4		/* 512 byte  for fiq mode of stack */
		msr 	cpsr, #0xD1
		mov	sp, r0
		sub	r0, #0
		msr	cpsr, #0xD7
		mov	sp, r0
		sub	r0, #0
		msr	cpsr, #0xDB
		mov	sp, r0
		sub	r0, #0
		msr	cpsr, #0x10
		mov	sp,r0			/* 1024 byte  for user mode of stack */

		b	main

		.align	5

irq_handler:
		sub  lr,lr,#4
		stmfd sp!,{r0-r12,lr}
		@bl	do_irq
		ldmfd sp!,{r0-r12,pc}^

stackpointer:
		.word	stack + 4 * 512

		.data
stack:		.space	4 * 512

		.end

map.lds，其中代码段让start.o位于text的最前面

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
/*OUTPUT_FORMAT("elf32-arm", "elf32-arm", "elf32-arm")*/
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
	. = 0x20008000;
	. = ALIGN(4);
	.text      :
	{
		start.o(.text)
		*(.text)
	}
	. = ALIGN(4);
    .rodata : 
	{ *(.rodata) }
    . = ALIGN(4);
    .data : 
	{ *(.data) }
    . = ALIGN(4);
    .bss :
     { *(.bss) }
}

Makefile

all:
	arm-cortex_a8-linux-gnueabi-gcc -fno-builtin -nostdinc -c -o start.o start.S
	arm-cortex_a8-linux-gnueabi-gcc -fno-builtin -nostdinc -c -o main.o main.c
	arm-cortex_a8-linux-gnueabi-ld start.o main.o -Tmap.lds -o test.elf
	arm-cortex_a8-linux-gnueabi-objcopy -O binary  test.elf test.bin
	arm-cortex_a8-linux-gnueabi-objdump -D test.elf > test.dis
	sudo cp test.bin /var/lib/tftpboot
clean:
	rm -rf start.o main.o test.elf test.bin test.dis

arm-cortex_a8-linux-gnueabi-objcopy -O binary  test.elf test.bin

arm-cortex_a8-linux-gnueabi-objdump -D test.elf > test.dis

工程源码：点击打开链接

基于Cortex-A8裸机，点亮LED灯程序分析,布布扣,bubuko.com

基于Cortex-A8裸机，点亮LED灯程序分析

原文：http://blog.csdn.net/it_liuwei/article/details/22419555