1. 看门狗原理
Watchdog原理上就是一个定时器。定时器timer对时钟进行计数，当定时器溢出时，产生复位信号，使得整个系统复位。在程序或嵌入式系统中，需要 定期的对看门狗timer进行复位重新计数，定时器不会溢出复位系统，从而保证系统的正常运行。当某种原因（例如干扰）引起程序跑飞或者进入死循环时，程 序不能定期的复位看门狗timer, 计数溢出产生复位信号，导致系统复位。
设本系统程序完整运行一周期的时间是T1，看门狗的定时周期为T2，T2>T1，在程序运行一周期后就修改定时器的计数值，只要程序正常运行，定时 器就不会溢出，若因为程序“跑飞”或者进入死循环，那么系统不能在T1时刻修改时间的计数值，一直计数直到T2时刻溢出，引发系统复位，使系统重新运行， 从而起到监控作用。
从上面的解释中可以看出，Watchdog的作用就是为了防止系统因意外“跑飞”，导致整个系统瘫痪时，恢复(reset)系统运行。
2. Tiny4412看门狗控制
1)作为常规定时器使用，并且可以产生中断
2)作为看门狗定时器使用，期满时，它可以产生128个时钟周期的复位信号
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。
看门狗定时器计数值的计算公式如下：
1)输入到计数器的时钟周期
t_watchdog = 1/( PCLK / (Prescaler value + 1) / Division_factor )
预分频器Prescaler及分频因子Division factor的值由用户在WTCON（看门狗时钟控制寄存器)中设置。
2)看门狗的定时周期
T = 计数值（WTCNT初值-WTCNT当前值） * t_watchdog
WTCNT为看门狗数据寄存器，用来设置计数多少个时钟周期。乘以时钟周期就是定时的总时间了。
具体代码：
1 #include "regs.h"
2
3 int (*printf)(char *, ...) = 0xc3e114d8;
4
5 void init_ttb(unsigned long *ttb);
6 void enable_mmu(void);
7 void memcpy(unsigned char *dest, unsigned char *source, int len);
8 void do_irq();
9
10 int main()
11 {
12
13 enable_mmu();
14 *(unsigned long *)0x67000000 = do_irq;
15 unsigned long source = 0;
16 __asm__ __volatile__(
17 "ldr %0, =vector_start\n"
18 : "=r" (source)
19 );
20 memcpy(0, source, 0x1000);
21
22 //step 1: set cpsr i bit
23 __asm__ __volatile__(
24 "mrs r0, cpsr\n"
25 "bic r0, r0, #0x80\n"
26 "msr cpsr, r0\n"
27 ::: "r0"
28 );
29
30 //step 2: enable gic
31 ICCICR_CPU0 = 1;//终端总开关
32 ICCPMR_CPU0 = 0xff;//设置最低优先级
33
34 ICDDCR = 1;
35 ICDIPR18_CPU0 &= ~(0xff << 24);//设置本中断优先级
36 ICDIPTR18_CPU0 &= ~(0xff << 24);// 选择指定的cpu0进行终端处理
37 ICDIPTR18_CPU0 |= (1 << 24);// 选择指定的cpu0进行终端处理
38 ICDISER2_CPU0 = (1 << 11);//设置本中断开启
39
40 //step 3: open interrupt source
41 GPM4CON = 0x1111;
42
43 WTCON = 0 | (1 << 2) | (0 << 3 ) | (1 << 5) | (254 << 8);
44 WTDAT = 0x4000;
45 printf("send sgi\n");
46 }
47
48 void do_irq()
49 {
50 printf("watch dog \n");
51
52 static unsigned long tmp = 0xf;
53 GPM4DAT = ~tmp;
54 tmp = GPM4DAT;
55
56 WTCLRINT = 0x1;
57
58 }
59
60 __asm__(
61 "vector_start:\n"
62 "b reset\n"
63 "b undef\n"
64 "b swi\n"
65 "b pre_abt\n"
66 "b data_abt\n"
67 ".word 0x0\n"
68 "b irq \n"
69 "b fiq\n"
70 "\n"
71 "reset:\n"
72 "undef:\n"
73 "mov sp, #0x66000000\n"
74 "stmfd sp!, {r0-r12, lr}\n"
75 "\n"
76 "mov r0, #0x67000000\n"
77 "ldr r1, [r0]\n"
78 "blx r1\n"
79 "\n"
80 "mov sp, #0x66000000\n"
81 "ldmea sp, {r0-r12, pc}^\n"
82 "swi:\n"
83 "mov sp, #0x66000000\n"
84 "stmfd sp!, {r0-r12, lr}\n"
85 "\n"
86 "mov r0, #0x67000000\n"
87 "ldr r1, [r0]\n"
88 "blx r1\n"
89 "\n"
90 "mov sp, #0x66000000\n"
91 "ldmea sp, {r0-r12, pc}^\n"
92 "\n"
93 "pre_abt:\n"
94 "data_abt:\n"
95 "mov sp, #0x66000000\n"
96 "sub lr, lr, #4\n"
97 "stmfd sp!, {r0-r12, lr}\n"
98 "\n"
99 "mov r0, #0x67000000\n"
100 "ldr r1, [r0]\n"
101 "blx r1\n"
102 "\n"
103 "mov sp, #0x66000000\n"
104 "ldmea sp, {r0-r12, pc}^\n"
105 "irq:\n"
106 "mov sp, #0x66000000\n"
107 "sub lr, lr, #4\n"
108 "stmfd sp!, {r0-r12, lr}\n"
109
110 "mov r0, #0x67000000\n"
111 "ldr r1, [r0]\n"
112 "blx r1\n"
113
114 "mov sp, #0x66000000\n"
115 "ldmea sp, {r0-r12, pc}^\n"
116 "fiq:\n"
117
118 );
119
120 void init_ttb(unsigned long *ttb)
121 {
122 unsigned long va = 0;
123 unsigned long pa = 0;
124
125 //00000000~10000000 -> 60000000~64000000
126 for(va=0x00000000; va<0x10000000; va+=0x100000){
127 pa = va + 0x60000000;
128 ttb[va >> 20] = pa | 2;
129 }
130
131 //10000000~14000000 -> 10000000~14000000
132 for(va=0x10000000; va<0x14000000; va+=0x100000){
133 pa = va;
134 ttb[va >> 20] = pa | 2;
135 }
136
137 //40000000~80000000 -> 40000000~80000000
138 for(va=0x40000000; va<0x80000000; va+=0x100000){
139 pa = va;
140 ttb[va >> 20] = pa | 2;
141 }
142
143 //30000000~40000000 -> 50000000~60000000
144 for(va=0x30000000; va<0x40000000; va+=0x100000){
145 pa = va + 0x20000000;
146 ttb[va >> 20] = pa | 2;
147 }
148 }
149
150 void enable_mmu(void)
151 {
152 unsigned long ttb = 0x70000000;
153 init_ttb(ttb);
154 unsigned long mmu = 0;
155 mmu = 1 | (1 << 3) | (1 << 8);
156 __asm__ __volatile__(
157 "mov r0, #3\n"
158 "mcr p15, 0, r0, c3, c0, 0\n"
159 "mcr p15, 0, %0, c2, c0, 0\n"
160 "mcr p15, 0, %1, c1, c0, 0\n"
161 :
162 : "r" (ttb), "r" (mmu)
163 );
164 }
165
166 void memcpy(unsigned char *dest, unsigned char *source, int len)
167 {
168 int i = 0;
169 for(i=0; i<len; i++)
170 dest[i] = source[i];
171 }
1 #define gpiobase 0x11000000 2 #define GPM4CON (*(volatile unsigned long *)(gpiobase + 0x02E0)) 3 #define GPM4DAT (*(volatile unsigned long *)(gpiobase + 0x02E4)) 4 #define GPX3CON (*(volatile unsigned long *)(gpiobase + 0x0C60)) 5 #define GPX3DAT (*(volatile unsigned long *)(gpiobase + 0x0C64)) 6 7 #define ICC 0x10480000 8 9 #define ICCICR_CPU0 (*(volatile unsigned long *)(ICC + 0x0000)) 10 #define ICCPMR_CPU0 (*(volatile unsigned long *)(ICC + 0x0004)) 11 #define ICCBPR_CPU0 (*(volatile unsigned long *)(ICC + 0x0008)) 12 #define ICCIAR_CPU0 (*(volatile unsigned long *)(ICC + 0x000C)) 13 #define ICCEOIR_CPU0 (*(volatile unsigned long *)(ICC + 0x0010)) 14 #define ICCRPR_CPU0 (*(volatile unsigned long *)(ICC + 0x0014)) 15 #define ICCHPIR_CPU0 (*(volatile unsigned long *)(ICC + 0x0018)) 16 #define ICCABPR_CPU0 (*(volatile unsigned long *)(ICC + 0x001C)) 17 #define INTEG_EN_C_CPU0 (*(volatile unsigned long *)(ICC + 0x0040)) 18 #define ICCIIDR (*(volatile unsigned long *)(ICC + 0x00FC)) 19 20 #define ICD 0x10490000 21 22 #define ICDDCR (*(volatile unsigned long *)(ICD + 0x0000)) 23 #define ICDICTR (*(volatile unsigned long *)(ICD + 0x0004)) 24 #define ICDIIDR (*(volatile unsigned long *)(ICD + 0x0008)) 25 #define ICDISR0_CPU0 (*(volatile unsigned long *)(ICD + 0x0080)) 26 #define ICDISER0_CPU0 (*(volatile unsigned long *)(ICD + 0x0100)) 27 #define ICDISER2_CPU0 (*(volatile unsigned long *)(ICD + 0x0108)) 28 #define ICDICER0_CPU0 (*(volatile unsigned long *)(ICD + 0x0180)) 29 #define ICDISPR0_CPU0 (*(volatile unsigned long *)(ICD + 0x0200)) 30 #define ICDICPR0_CPU0 (*(volatile unsigned long *)(ICD + 0x0280)) 31 #define ICDABR0_CPU0 (*(volatile unsigned long *)(ICD + 0x0300)) 32 #define ICDIPR0_CPU0 (*(volatile unsigned long *)(ICD + 0x0400)) 33 #define ICDIPR1_CPU0 (*(volatile unsigned long *)(ICD + 0x0404)) 34 #define ICDIPR2_CPU0 (*(volatile unsigned long *)(ICD + 0x0408)) 35 #define ICDIPR3_CPU0 (*(volatile unsigned long *)(ICD + 0x040C)) 36 #define ICDIPR4_CPU0 (*(volatile unsigned long *)(ICD + 0x0410)) 37 #define ICDIPR5_CPU0 (*(volatile unsigned long *)(ICD + 0x0414)) 38 #define ICDIPR6_CPU0 (*(volatile unsigned long *)(ICD + 0x0418)) 39 #define ICDIPR7_CPU0 (*(volatile unsigned long *)(ICD + 0x041C)) 40 #define ICDIPR18_CPU0 (*(volatile unsigned long *)(ICD + 0x0448)) 41 42 #define ICDIPTR0_CPU0 (*(volatile unsigned long *)(ICD + 0x0800)) 43 #define ICDIPTR1_CPU0 (*(volatile unsigned long *)(ICD + 0x0804)) 44 #define ICDIPTR18_CPU0 (*(volatile unsigned long *)(ICD + 0x0848)) 45 #define ICDSGIR (*(volatile unsigned long *)(ICD + 0x0F00)) 46 47 48 #define WTCON (*(volatile unsigned long *)0x10060000) 49 #define WTDAT (*(volatile unsigned long *)0x10060004) 50 #define WTCNT (*(volatile unsigned long *)0x10060008) 51 #define WTCLRINT (*(volatile unsigned long *)0x1006000C)
时间： 2024-10-21 14:38:23