Tiny4412中断之看门狗

　　一：看门狗（WDT watch dog timer）

　　看门狗其实是一个计数器，它的作用就是防止程序陷入死循环或者程序运行跑飞；看门狗是一个硬件，它的工作原理是，初始化给他一个值，它会过一段时间减一，直到这个数减为0，它将会产生一个中断信号或者reset信号，致使我们系统复位，而又时候我们不想让它过一会儿就重启又想预防死机，那么我们就可以在这个数减到快要接进0的时候，给它重新赋值；这样就不会触发reset信号，但当程序跑飞时机器死机时，它就会减到零，进行操作系统复位；

　 具体看下图所示：输入时钟为PCLK（该时钟频率等于系统的主频），它经过两级分频(Prescaler和frequency division factor)，最后将分频后的时钟作为该定时器的输入时钟，当计数器期满后可以产生中断或者复位信号。

　　看门狗计数器公式如下：

　　t_watchdog = 1/( PCLK / (Prescaler value + 1) / Division_factor )

　　通过tiny4412用户手册我们可以找到看门狗的中断号为75（如下图）：

　　预分频器Prescaler及分频因子Division factor的值在WTCON（看门狗时钟控制寄存器)中设置，如下图：

　　今天的程序是使用watchdog来实现led灯的闪烁，下面贴出代码：

#ifndef __BUNFLY_H
#define __BUNFLY_H

#define ICCICR_CPU0        (*(volatile unsigned long *)0x10480000)
#define ICCPMR_CPU0        (*(volatile unsigned long *)0x10480004)
#define ICDDCR            (*(volatile unsigned long *)0x10490000)
#define ICDIPR0_CPU0    (*(volatile unsigned long *)0x10490400)
#define ICDIPTR0_CPU0    (*(volatile unsigned long *)0x10490800)
#define ICDISER0_CPU0    (*(volatile unsigned long *)0x10490100)
#define ICDSGIR            (*(volatile unsigned long *)0x10490f00)
#define ICCEOIR_CPU0    (*(volatile unsigned long *)0x10480010)
#define ICCIAR_CPU0        (*(volatile unsigned long *)0x1048000c)
#define ICDIPR2_CPU0    (*(volatile unsigned long *)0x10490408)
#define ICDIPTR2_CPU0    (*(volatile unsigned long *)0x10490808)
#define ICDIPR3_CPU0    (*(volatile unsigned long *)0x1049040c)
#define ICDIPTR3_CPU0    (*(volatile unsigned long *)0x1049080c)
#define ICDIPR16_CPU0    (*(volatile unsigned long *)0x10490440)
#define ICDIPTR16_CPU0    (*(volatile unsigned long *)0x10490840)
#define ICDIPR18_CPU0    (*(volatile unsigned long *)0x10490448)
#define ICDIPTR18_CPU0    (*(volatile unsigned long *)0x10490848)
#define ICDISER2_CPU0    (*(volatile unsigned long *)0x10490108)

#define WTCON             (*(volatile unsigned long *)0x10060000)
#define WTDAT             (*(volatile unsigned long *)0x10060004)
#define WTCNT             (*(volatile unsigned long *)0x10060008)
#define WTCLRINT         (*(volatile unsigned long *)0x1006000C)

#define EXT_INT43CON    (*(volatile unsigned long *)0x11000e0c)
#define EXT_INT43_MASK    (*(volatile unsigned long *)0x11000f0c)
#define EXT_INT43_PEND    (*(volatile unsigned long *)0x11000f4c)
#define GPX3CON         (*(volatile unsigned long *)0x11000c60)

#define GPM4CON    (*(volatile unsigned long *)0x110002e0)
#define GPM4DAT (*(volatile unsigned long *)0x110002e4)

#endif    //__BUNFLY_H

#include "bunfly.h"

void (*udelay)(int) = 0xc3e25f90;
int (*printf)(char *, ...) = 0xc3e114d8;
void enable_mmu();
void init_table(unsigned long *addr);
void memcpy(unsigned char *dest, unsigned char *src, int len);
extern unsigned long  vector_start;
void do_irq();
void led_on();
void led_off();

int main()
{    
    memcpy(0x70000000, vector_start, 0x1000);    
    enable_mmu();

    *(unsigned long *)0x47000000 = do_irq;

    //step 1: set cpu permit interrupt
    __asm__ __volatile__(
        "mrs r0, cpsr
"
        "bic r0,r0, #0x80
"
        "msr cpsr, r0
"
        :::"r0"
    );

    //step 2: set GIC (cgi) enable
    ICCICR_CPU0 = 1; //中断总开关
    ICCPMR_CPU0 =0xff;//设置最低优先级（门槛）
    ICDDCR = 1; //本中断开关
    ICDIPR18_CPU0 = (100 << 24);//设置本中断优先级
    ICDIPTR18_CPU0 = (1 << 24);//选择指定的cpu进行中断处理
    ICDISER2_CPU0 = (1 << 11);//启用本中断
    
    //step 3: set watch dog timer
    WTCNT = 32768;
    WTDAT = 32768;
    WTCON = (1 << 2) | (3 << 3) | (1 << 5) | (95 << 8);
            
    printf("welcom back
");
}

void do_irq()
{
    WTCLRINT = 0;//清中断
    printf("wang wang wang
");
    static int flags = 1;
    if(flags) {
        led_on();
        flags = 0;
    }
    else {
        led_off();
        flags = 1;
    }
}

void led_on()
{
    GPM4CON &= ~0xffff;
    GPM4CON |= 0x1111;
    GPM4DAT &= ~0xf;
}

void led_off()
{

    GPM4CON &= ~0xffff;
    GPM4CON |= 0x1111;
    GPM4DAT |= 0xf;
}

void memcpy(unsigned char *dest, unsigned char *src, int len)
{
    int i = 0;
    for(i = 0; i < len; i++) {
        dest[i] = src[i];
    }
}

void enable_mmu()
{
    /*构建表*/
    unsigned long addr = 0x50000000;
    init_table(addr);
    /*打开mmu*/
    unsigned long mmu = 0;
    mmu = 1 | (1 << 1) | (1 << 3) | (1 << 8);
    __asm__ __volatile__ (
        "mov r0, #3
"
        "MCR p15, 0, r0, c3, c0, 0
"//设置为管理员
        "MCR p15, 0, %0, c2, c0, 0
"//设置表的地址
        "MCR p15, 0, %1, c1, c0, 0
"//开启mmu
        :    
        :    "r" (addr), "r" (mmu)
        :
    );

}

__asm__(

"vector: 
"
"    b reset
"
"    b und
"
"    b swi
"
"    b pre_abt
"
"    b data_abt
"
"    .word 0x0
"
"    b irq
"
"    b fiq
"
"reset:
"
"und:
"
"    mov sp, #0x47000000
"
"    stmdb sp!, {r0-r12, lr}
"

"    ldr r3, =0x47000004
"
"    ldr r2, [r3]
"
"    blx r2
"

"    mov sp, #0x47000000
"
"    ldmdb sp, {r0-r12, pc}^    
"

"swi:
"
"    mov sp, #0x47000000
"
"    stmdb sp!, {r0-r12, lr}^
"

"    mov sp, #0x47000000
"
"    ldmdb sp, {r0-r12, pc}^    
"

"pre_abt:
"

"data_abt:
"
"    mov sp, #0x47000000
"
"    sub lr, lr, #4
"
"    stmdb sp!, {r0-r12, lr}
"

"    ldr r3, =0x47000008
"
"    ldr r2, [r3]
"
"    blx r2
"

"    mov sp, #0x47000000
"
"    ldmdb sp, {r0-r12, pc}^    
"
"irq:
"

"    mov sp, #0x47000000
"
"    sub lr, lr, #4
"
"    stmdb sp!, {r0-r12, lr}
"

"    ldr r3, =0x47000000
"
"    ldr r2, [r3]
"
"    blx r2
"

"    mov sp, #0x47000000
"
"    ldmdb sp, {r0-r12, pc}^    
"

"fiq:
"

    ".global vector_start
"
"vector_start: 
"
    ".word vector 
 "

);

void init_table(unsigned long *addr)
{
    unsigned long va = 0;
    unsigned long phys = 0;

    //0x40000000-0x80000000 -> 0x40000000-0x80000000    
    for(va = 0x40000000; va < 0x80000000; va += 0x100000) {
        phys = va;
        addr[va >> 20] = phys | 2;
    }

    //0x10000000-0x14000000 -> 0x10000000-0x140000000    
    for(va = 0x10000000; va < 0x14000000; va += 0x100000) {
        phys = va;
        addr[va >> 20] = phys | 2;
    }
    //0x10000000-0x14000000 -> 0x10000000-0x140000000    
    for(va = 0x0; va < 0x10000000; va += 0x100000) {
        phys = va + 0x70000000;
        addr[va >> 20] = phys | 2;
    }
            
}