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;
}
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