中断法实现按键点灯



汇编代码

.global _start					/* 声明一个全局的标号 */
.global key_isr
_start:
	/* 设置栈，以调用c函数 */
	ldr	sp, =0x40000000		

	/* 开总中断	*/
	mrs r0, cpsr
	bic r0, r0, #0x00000080		/* 清楚第7位，IRQ中断禁止位，写0使能IRQ */
	msr cpsr, r0

	bl main						/* 跳转到C函数去执行 */

halt:
	b halt

key_isr:
	/* 计算返回地址:PC的值等于当前执行的地址+8，当CPU正要执行某条指令时（还未执行），被中断，
	** 这是这条刚要执行的指令的地址刚好=PC-4 */
	sub lr, lr, #4
	stmfd sp!, {r0-r12, lr}  	/* 保护现场 */
	bl key_handle
	/* 恢复现场 */
	ldmfd sp!, {r0-r12, pc}^  	/* ^表示把spsr恢复到cpsr */

C语言部分的代码

#define GPC0CON				*((volatile unsigned int *)0xE0200060)
#define GPC0DAT				*((volatile unsigned int *)0xE0200064)

#define GPH0CON				*((volatile unsigned int *)0xE0200C00)
#define GPH0DAT				*((volatile unsigned int *)0xE0200C04)

#define EXT_INT_0_CON 		*((volatile unsigned int *)0xE0200E00)
#define EXT_INT_0_MASK		*((volatile unsigned int *)0xE0200F00)

#define VIC0INTSELECT		*((volatile unsigned int *)0xF200000C)
#define VIC0INTENABLE 		*((volatile unsigned int *)0xF2000010)

#define VIC0VECTADDR0		*((volatile unsigned int *)0xF2000100)
#define VIC0VECTADDR1		*((volatile unsigned int *)0xF2000104)

#define VIC0ADDRESS  		*((volatile unsigned int *)0xF2000F00)

#define EXT_INT_0_PEND		*((volatile unsigned int *)0xE0200F40)

extern void key_isr(void);

void key_handle()
{	
	volatile unsigned char key_code = EXT_INT_0_PEND & 0x3;
	
	VIC0ADDRESS = 0;		/* 清中断向量寄存器 */
	EXT_INT_0_PEND |= 3;	/* 清中断挂起寄存器 */
	
	if (key_code == 1)		/* key1 */
		GPC0DAT ^= 1 << 3;	/* toggle LED1 */
	else if (key_code == 2)	/* key2 */
		GPC0DAT ^= 1 << 4;	/* toggle LED2 */
}

int main()
{
	GPC0CON &= ~(0xFF << 12);
	GPC0CON |= 0x11 << 12;					/* 配置GPC0_3和GPC0_4为输出：LED1和LED2 */
	GPH0CON |= 0xFF << 0;					/* 配置GPH0_0和GPH0_1为外部中断：key1和key2 */
	
	EXT_INT_0_CON &= ~(0xFF << 0);
	EXT_INT_0_CON |= 2 | (2 << 4);			/* 配置EXT_INT[0]和EXT_INT[1]为下降沿触发 */
	EXT_INT_0_MASK &= ~3;					/* 取消屏蔽外部中断EXT_INT[0]和EXT_INT[1] */
	
	VIC0INTSELECT &= ~3;					/* 选择外部中断EXT_INT[0]和外部中断EXT_INT[1]为IRQ类型的中断 */
	
	VIC0INTENABLE |= 3;						/* 使能外部中断EXT_INT[0]和EXT_INT[1] */
	
	VIC0VECTADDR0 = (int)key_isr;			/* 当EXT_INT[0]触发中断，即用户按下key1时，
											 CPU就会自动的将VIC0VECTADDR0的值赋给VIC0ADDRESS并跳转到这个地址去执 */
	VIC0VECTADDR1 = (int)key_isr;
	
	while (1);
	
	return 0;
}