看门狗（watchdog ）分硬件看门狗和软件看门狗。硬件看门狗是利用一个定时器 电路，其定时输出连接到电路的复位端，程序在一定时间范围内对定时器清零 （俗称 “喂狗”），如果程序出现故障，不在定时周期内复位看门狗，就使得看门狗定时器溢出产生复位信号 并重启系统。软件看门狗原理上一样，只是将硬件电路上的定时器用处理器的内部定 时器代替。
1 看门狗的三个寄存器
1.1 watchdog原理
S3C2410内部集成了watchdog，提供3 个寄存器对watchdog 进行操作，这3 个寄存器分别为WTCON （watchdog 控制寄存器）、WTDAT （watchdog 数据寄存器）和WTCNT(watchdog 记数寄存器) S3c2440的看门狗的原理框图如下：
可以看到，看门狗定时器的频率由PCLK提供，其预分频器最大取值为255+1；另外，通过MUX，可以进一步降低频率。定时器采用递减模式，一旦到0，则可以触发看门狗中断以及RESET复位信号。 看门狗定时器的频率的计算公式如下：
t_watchdog = 1/[PCLK/(Prescaler value + 1)/Division_factor]
1.2 开启S3C2410 的看门狗
void enable watchdog () { rWTCON = WTCON DIV64 | WTCON RSTEN;//64分频、开启复位信号 rWTDAT = 0x8000;//计数目标 rWTCON |= WTCON ENABLE;//开启看门狗 } 1.3 S3C2410 的看门狗 “喂狗”
void feed dog () { rWTCNT=0x8000; } 1.4 看门狗的使用例程
void main () { init system (); ... enable watchdog ();//启动看门狗 ... while (1) { ... feed dog (); //喂狗 } } 2 watchdog中的数据结
有一类设备被称为 “平台设备”，通常 SoC 系统中集成的独立的外设单元都被当作平台设备处理
2.1 platform_device 结构体
struct platform device { const char * name;//设备名 u32 id; struct device dev; u32 num resources;//设备所使用各类资源数量 struct resource * resource;//资源 }; 2.2 S3C2410 中的平台设备
struct platform device *s3c24xx uart devs[];struct platform device s3c device usb; //USB 控制器 struct platform device s3c device lcd; //LCD 控制器 struct platform device s3c device wdt; //看门狗 2 struct platform device s3c device i2c; //I C 控制器 struct platform device s3c device iis; //IIS struct platform device s3c device rtc; //实时钟 ... /*SMDK2410开发板使用的平台设备*/ static struct platform device *smdk2410 devices[] initdata = { &s3c device usb, //USB &s3c device lcd, //LCD &s3c device wdt, //看门狗 &s3c device i2c, //I C &s3c device iis, //IIS }; 2.3 S3C2410 看门狗的platform_device 结构体
struct platform device s3c device wdt = { .name = "s3c2410-wdt", //设备名 .id = - 1, . num resources = ARRAY SIZE (s3c wdt resource), //资源数量 .resource = s3c wdt resource, //看门狗所使用资源 }; 2.4 int platform_add_devices()函数
int platform add devices(struct platform device **devs, int num) { int i, ret = 0; for (i = 0; i < num; i++) { ret = platform device register(devs[i]);/*注册平台设备*/ if (ret) /*注册失败*/ { while (--i >= 0) platform device unregister(devs[i]);/*注销已经注册的平台设备 */ break; } } return ret; } 2.5 platform_driver 结构体
struct platform driver { int (*probe)(struct platform device *);//探测 int (*remove)(struct platform device *);//移除 void (*shutdown)(struct platform device *);//关闭 int (*suspend)(struct platform device *, pm message t state);// 挂起 int (*resume)(struct platform device *);//恢复 struct device driver driver; }; 2.6 S3C2410 看门狗的platform_driver 结构体
static struct platform driver s3c2410wdt driver = { .probe = s3c2410wdt probe,//S3C2410看门狗探测 .remove = s3c2410wdt remove,// S3C2410看门狗移除 .shutdown = s3c2410wdt shutdown,//S3C2410看门狗关闭 .suspend = s3c2410wdt suspend,//S3C2410看门狗挂起 .resume = s3c2410wdt resume, //S3C2410看门狗恢复 .driver = { .owner = THIS MODULE, .name = "s3c2410-wdt",//设备名 }, }； 2.7 S3C2410 看门狗所用资源
static struct resource s3c wdt resource[] = { [0] = { .start = S3C24XX PA WATCHDOG, //看门狗I/O 内存开始位置 .end = S3C24XX PA WATCHDOG + S3C24XX SZ WATCHDOG - 1, //看门狗I/O 内存结束位置 .flags = IORESOURCE MEM, //I/O 内存资源 } , [1] = { .start = IRQ WDT, //看门狗开始IRQ 号 .end = IRQ WDT, //看门狗结束IRQ 号 .flags = IORESOURCE IRQ, //IRQ 资源 } }; 2.8 S3C2410 看门狗驱动的miscdevice 结构体
static struct miscdevice s3c2410wdt miscdev = { .minor = WATCHDOG MINOR,//次设备号 .name = "watchdog", .fops = &s3c2410wdt fops,//文件操作结构体 }; 2.9 S3C2410 看门狗驱动的文件操作结构体
static struct file operations s3c2410wdt fops = { .owner = THIS MODULE, .llseek = no llseek, //seek .write = s3c2410wdt write, //写函数 .ioctl = s3c2410wdt ioctl, //ioctl 函数 .open = s3c2410wdt open, //打开函数 .release = s3c2410wdt release,//释放函数 }; 3 加载和卸载函数
驱动模块的加载和卸载函数分别 用 platform_driver_register() 和 platform_driver_ unregister()注册和注销platform_driver
3.1 S3C2410 看门狗驱动
static int __init watchdog__init (void) { printk (banner); return platform driver register(&s3c2410wdt driver);// 注 册platform driver } static void exit watchdog exit (void) { platform driver unregister (&s3c2410wdt driver);// 注 销 platform driver } 4 探测和移除函数
4.1 探测函数
static int s3c2410wdt probe (struct platform device *pdev) { struct resource *res; int started = 0; int ret; int size; DBG ("%s: probe=%p\n", _ _FUNCTION_ _, pdev); /* 获得看门狗的内存区域 */ res = platform get resource (pdev, IORESOURCE MEM, 0); if (res == NULL) { printk(KERN INFO PFX "failed to get memory region resouce\n"); return - ENOENT; } size = (res->end - res->start) + 1; //申请I/O 内存 wdt mem = request mem region (res->start, size, pdev->name); if (wdt mem == NULL) { printk(KERN INFO PFX "failed to get memory region\n"); return - ENOENT; } wdt base = ioremap (res->start, size); //设备内存->虚拟地址 if (wdt base == 0) { printk(KERN INFO PFX "failed to ioremap () region\n"); return - EINVAL; } DBG ("probe: mapped wdt base=%p\n", wdt base); /* 获得看门狗的中断 */ res = platform get resource (pdev, IORESOURCE IRQ, 0); if (res == NULL) { printk(KERN INFO PFX "failed to get irq resource\n"); return - ENOENT; } //申请中断 ret = request irq (res->start, s3c2410wdt irq, 0, pdev->name, pdev); if (ret != 0) { printk(KERN INFO PFX "failed to install irq (%d)\n", ret); return ret; } wdt clock = clk get (&pdev->dev, "watchdog"); //获得看门狗时钟源 if (wdt clock == NULL) { printk(KERN INFO PFX "failed to find watchdog clock source\n"); return - ENOENT; } clk enable (wdt clock); /* 看看是否能设置定时器的超时时间为期望的值，如果不能，使用缺省值 */ if (s3c2410wdt set heartbeat (tmr margin)) { started = s3c2410wdt set heartbeat ( CONFIG S3C2410 WATCHDOG DEFAULT TIME); if (started == 0) { printk (KERN INFO PFX "tmr margin value out of range, default %d used\n",CONFIG S3C2410 WATCHDOG DEFAULT TIME); } else { printk (KERN INFO PFX "default timer value is out of range, cannot start\n"); } } //注册miscdevice ret = misc register(&s3c2410wdt miscdev); if (ret) { printk(KERN ERR PFX "cannot registermiscdev on minor=%d (%d)\n", WATCHDOG MINOR, ret); return ret; } if (tmr atboot && started == 0) { printk(KERN INFO PFX "Starting Watchdog Timer\n"); s3c2410wdt start (); } return 0; } 4.2 探测函数
static int s3c2410wdt remove (struct platform device *dev) { if (wdt mem != NULL) { release resource (wdt mem); //释放资源 kfree (wdt mem);//释放内存 wdt mem = NULL; } //释放中断 if (wdt irq != NULL) { free irq (wdt irq->start, dev); wdt irq = NULL; } //禁止时钟源 if (wdt clock != NULL) { clk disable (wdt clock); clk put (wdt clock); wdt clock = NULL; } misc deregister(&s3c2410wdt miscdev);//注销miscdevice return 0; } 5 挂起和恢复函数
5.1 挂起函数
static int s3c2410wdt suspend (struct platform device *dev, pm message t state) { /* 保存看门狗状态，停止它 */ wtcon save = readl (wdt base + S3C2410 WTCON); wtdat save = readl (wdt base + S3C2410 WTDAT); s3c2410wdt stop (); return 0; } 5.2 恢复函数
static int s3c2410wdt resume (struct platform device *dev) { /* 恢复看门狗状态 */ writel (wtdat save, wdt base + S3C2410 WTDAT); writel (wtdat save, wdt base + S3C2410 WTCNT); writel (wtcon save, wdt base + S3C2410 WTCON); printk (KERN INFO PFX "watchdog %sabled\n", (wtcon save &S3C2410 WTCON ENABLE)? "en" : "dis"); return 0; } 6 打开和释放函数
6.1 打开函数
static int s3c2410wdt open (struct inode *inode, struct file *file) { if (down trylock (&open lock)) //获得打开锁 return - EBUSY; if (nowayout) { module get (THIS MODULE); } else { allow close = CLOSE STATE ALLOW; } /* 启动看门狗 */ s3c2410wdt start (); return nonseekable open (inode, file); } 6.2 释放函数
static int s3c2410wdt release (struct inode *inode,struct file *file) { /* 停止看门狗 */ if (allow close == CLOSE STATE ALLOW) { s3c2410wdt stop (); } else { printk (KERN CRIT PFX "Unexpected close, not stopping watchdog!\n"); s3c2410wdt keepalive (); } allow close = CLOSE STATE NOT; up (&open lock); //释放打开锁 return 0; } 7 启停watchdog函数和写函数
7.1 启停看门狗函数
/*停止看门狗*/ static int s3c2410wdt stop (void) { unsigned long wtcon; wtcon = readl(wdt base + S3C2410 WTCON); //停止看门狗，禁止复位 wtcon &= ~ (S3C2410 WTCON ENABLE | S3C2410 WTCON RSTEN); writel (wtcon, wdt base + S3C2410 WTCON); return 0; } /*开启看门狗*/ static int s3c2410wdt start (void) { unsigned long wtcon; s3c2410wdt stop (); wtcon = readl(wdt base + S3C2410 WTCON); //使能看门狗，128 分频 wtcon |= S3C2410 WTCON ENABLE | S3C2410 WTCON DIV128; if (soft noboot) { wtcon |= S3C2410 WTCON INTEN; //使能中断 wtcon &= ~S3C2410 WTCON RSTEN; //禁止复位 } else { wtcon &= ~S3C2410 WTCON INTEN; //禁止中断 wtcon |= S3C2410 WTCON RSTEN; //使能复位 } DBG ("%s: wdt count=0x%08x, wtcon=%08lx\n", FUNCTION , wdt count, wtcon); writel (wdt count, wdt base + S3C2410 WTDAT); writel (wdt count, wdt base + S3C2410 WTCNT); writel (wtcon, wdt base + S3C2410 WTCON); return 0; } 7.2 写函数
static ssize t s3c2410wdt write (struct file *file, const char user *data, size t len, loff t *ppos) { /* 刷新看门狗 */ if (len) { if (!nowayout) { size t i; allow close = CLOSE STATE NOT; for (i = 0; i != len; i++) { char c; if (get user(c, data + i))//用户空间->内核空间 return - EFAULT; if (c == 'V ') //如果写入了'V ' ，允许关闭 allow close = CLOSE STATE ALLOW; } } s3c2410wdt keepalive (); } return len; } 版权所有，转载请注明转载地址：