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\n"
         "bic r0,r0, #0x80\n"
         "msr cpsr, r0\n"
         :::"r0"
     );
 
     //step 2: set GIC (cgi) enable
     ICCICR_CPU0 = ; //中断总开关
     ICCPMR_CPU0 =0xff;//设置最低优先级（门槛）
     ICDDCR = ; //本中断开关
     ICDIPR18_CPU0 = ( << );//设置本中断优先级
     ICDIPTR18_CPU0 = ( << );//选择指定的cpu进行中断处理
     ICDISER2_CPU0 = ( << );//启用本中断
 
     //step 3: set watch dog timer
     WTCNT = ;
     WTDAT = ;
     WTCON = ( << ) | ( << ) | ( << ) | ( << );
 
     printf("welcom back\n");
 }
 
 void do_irq()
 {
     WTCLRINT = ;//清中断
     printf("wang wang wang\n");
     static int flags = ;
     if(flags) {
         led_on();
         flags = ;
     }
     else {
         led_off();
         flags = ;
     }
 }
 
 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 = ;
     for(i = ; 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 = ;
     mmu =  | ( << ) | ( << ) | ( << );
     __asm__ __volatile__ (
         "mov r0, #3\n"
         "MCR p15, 0, r0, c3, c0, 0\n"//设置为管理员
         "MCR p15, 0, %0, c2, c0, 0\n"//设置表的地址
         "MCR p15, 0, %1, c1, c0, 0\n"//开启mmu
         :
         :    "r" (addr), "r" (mmu)
         :
     );
 
 }
 
 __asm__(
 
 "vector: \n"
 "    b reset\n"
 "    b und\n"
 "    b swi\n"
 "    b pre_abt\n"
 "    b data_abt\n"
 "    .word 0x0\n"
 "    b irq\n"
 "    b fiq\n"
 "reset:\n"
 "und:\n"
 "    mov sp, #0x47000000\n"
 "    stmdb sp!, {r0-r12, lr}\n"
 
 "    ldr r3, =0x47000004\n"
 "    ldr r2, [r3]\n"
 "    blx r2\n"
 
 "    mov sp, #0x47000000\n"
 "    ldmdb sp, {r0-r12, pc}^    \n"
 
 "swi:\n"
 "    mov sp, #0x47000000\n"
 "    stmdb sp!, {r0-r12, lr}^\n"
 
 "    mov sp, #0x47000000\n"
 "    ldmdb sp, {r0-r12, pc}^    \n"
 
 "pre_abt:\n"
 
 "data_abt:\n"
 "    mov sp, #0x47000000\n"
 "    sub lr, lr, #4\n"
 "    stmdb sp!, {r0-r12, lr}\n"
 
 "    ldr r3, =0x47000008\n"
 "    ldr r2, [r3]\n"
 "    blx r2\n"
 
 "    mov sp, #0x47000000\n"
 "    ldmdb sp, {r0-r12, pc}^    \n"
 "irq:\n"
 
 "    mov sp, #0x47000000\n"
 "    sub lr, lr, #4\n"
 "    stmdb sp!, {r0-r12, lr}\n"
 
 "    ldr r3, =0x47000000\n"
 "    ldr r2, [r3]\n"
 "    blx r2\n"
 
 "    mov sp, #0x47000000\n"
 "    ldmdb sp, {r0-r12, pc}^    \n"
 
 "fiq:\n"
 
     ".global vector_start\n"
 "vector_start: \n"
     ".word vector \n "
 
 );
 
 void init_table(unsigned long *addr)
 {
     unsigned long va = ;
     unsigned long phys = ;
 
     //0x40000000-0x80000000 -> 0x40000000-0x80000000
     for(va = 0x40000000; va < 0x80000000; va += 0x100000) {
         phys = va;
         addr[va >> ] = phys | ;
     }
 
     //0x10000000-0x14000000 -> 0x10000000-0x140000000
     for(va = 0x10000000; va < 0x14000000; va += 0x100000) {
         phys = va;
         addr[va >> ] = phys | ;
     }
     //0x10000000-0x14000000 -> 0x10000000-0x140000000
     for(va = 0x0; va < 0x10000000; va += 0x100000) {
         phys = va + 0x70000000;
         addr[va >> ] = phys | ;
     }
 
 }