努力成为linux kernel hacker的人李万鹏原创作品，为梦而战。转载请标明出处
<a href="http://blog.csdn.net/woshixingaaa/archive/2011/05/21/6436215.aspx">http://blog.csdn.net/woshixingaaa/archive/2011/05/21/6436215.aspx</a>
RTC(实时时钟)是一种典型的字符设备，作为一种字符设备驱动，RTC需要有file_operations中接口函数的实现，如open(),release(),read(),poll(),ioctl()等,而典型的ioctl包括RTC_SET_TIME,RTC_ALM_READ,RTC_ALM_SET,RTC_IRQP_SET,RTC_IRQP_READ等，这些对于所有的RTC是通用的，只有底层的具体实现是设备相关的。如下图可以清楚看出RTC子系统的框架。
下面介绍几个重要的数据结构：
rtc_device用来描述rtc设备：
C-sharp代码
struct rtc_device
{
struct device dev;
struct module *owner;
int id; //RTC设备的次设备号
char name[RTC_DEVICE_NAME_SIZE];
const struct rtc_class_ops *ops;
struct mutex ops_lock;
struct cdev char_dev;
unsigned long flags;
unsigned long irq_data;
spinlock_t irq_lock;
wait_queue_head_t irq_queue;
struct fasync_struct *async_queue;
struct rtc_task *irq_task;
spinlock_t irq_task_lock;
int irq_freq;
int max_user_freq;
#ifdef CONFIG_RTC_INTF_DEV_UIE_EMUL
struct work_struct uie_task;
struct timer_list uie_timer;
/* Those fields are protected by rtc->irq_lock */
unsigned int oldsecs;
unsigned int uie_irq_active:1;
unsigned int stop_uie_polling:1;
unsigned int uie_task_active:1;
unsigned int uie_timer_active:1;
#endif
};
rtc_time用于get time/set time：
struct rtc_time {
int tm_sec;
int tm_min;
int tm_hour;
int tm_mday;
int tm_mon;
int tm_year;
int tm_wday;
int tm_yday;
int tm_isdst;
描述报警状态的结构：
struct rtc_wkalrm {
unsigned char enabled; /* 0 = alarm disabled, 1 = alarm enabled */
unsigned char pending; /* 0 = alarm not pending, 1 = alarm pending */
struct rtc_time time; /* time the alarm is set to */
struct rtc_class_ops {
int (*open)(struct device *); //打开设备时的回调函数，这个函数应该初始化硬件并申请资源
void (*release)(struct device *); //这个函数是设备关闭时被调用的，应该注销申请的资源
int (*ioctl)(struct device *, unsigned int, unsigned long); //ioctl函数，对想让RTC自己实现的命令应返回ENOIOCTLCMD
int (*read_time)(struct device *, struct rtc_time *); //读取时间
int (*set_time)(struct device *, struct rtc_time *); //设置时间
int (*read_alarm)(struct device *, struct rtc_wkalrm *); //读取下一次定时中断的时间
int (*set_alarm)(struct device *, struct rtc_wkalrm *); //设置下一次定时中断的时间
int (*proc)(struct device *, struct seq_file *); //procfs接口
int (*set_mmss)(struct device *, unsigned long secs); //将传入的参数secs转换为struct rtc_time然后调用set_time函数。程序员可以不实现这个函数，但
前提是定义好了read_time/set_time，因为RTC框架需要用这两个函数来实现这个功能。
int (*irq_set_state)(struct device *, int enabled); //周期采样中断的开关，根据enabled的值来设置
int (*irq_set_freq)(struct device *, int freq); //设置周期中断的频率
int (*read_callback)(struct device *, int data); ///用户空间获得数据后会传入读取的数据，并用这个函数返回的数据更新数据。
int (*alarm_irq_enable)(struct device *, unsigned int enabled); //alarm中断使能开关，根据enabled的值来设置
int (*update_irq_enable)(struct device *, unsigned int enabled); //更新中断使能开关，根据enabled的值来设置
现在来看看rtc子系统是怎么注册上的：
static int __init rtc_init(void)
rtc_class = class_create(THIS_MODULE, "rtc");
if (IS_ERR(rtc_class)) {
printk(KERN_ERR "%s: couldn't create class\n", __FILE__);
return PTR_ERR(rtc_class);
}
rtc_class->suspend = rtc_suspend;
rtc_class->resume = rtc_resume;
rtc_dev_init();
rtc_sysfs_init(rtc_class);
return 0;
}
void __init rtc_dev_init(void)
int err;
err = alloc_chrdev_region(&rtc_devt, 0, RTC_DEV_MAX, "rtc");
if (err < 0)
printk(KERN_ERR "%s: failed to allocate char dev region\n",
__FILE__);
在class.c文件函数rtc_init中生成rtc类，然后调用rtc-dev.c文件中的rtc_dev_init分配设备号。
在rtc-dev.c中声明了file_operations,因为rtc也是一个字符设备:
static const struct file_operations rtc_dev_fops = {
.owner = THIS_MODULE,
.llseek = no_llseek,
.read = rtc_dev_read,
.poll = rtc_dev_poll,
.unlocked_ioctl = rtc_dev_ioctl,
.open = rtc_dev_open,
.release = rtc_dev_release,
.fasync = rtc_dev_fasync,
下面来分析rtc-s3c.c源码：
首先看模块的注册和撤销：
static int __init s3c_rtc_init(void)
printk(banner);
return platform_driver_register(&s3c2410_rtc_driver);
static void __exit s3c_rtc_exit(void)
platform_driver_unregister(&s3c2410_rtc_driver);
从上边的代码可以看出rtc driver作为platform_driver注册进内核，挂在platform_bus上。
static struct platform_driver s3c2410_rtc_driver = {
.probe = s3c_rtc_probe, //rtc探测函数
.remove = __devexit_p(s3c_rtc_remove), //rtc移除函数
.suspend = s3c_rtc_suspend, //rtc挂起函数
.resume = s3c_rtc_resume, //rtc恢复函数
.driver = {
.name = "s3c2410-rtc", //注意这里的名字一定要和系统中定义平台设备的地方一致，这样才能把平台设备和平台驱动关联起来
.owner = THIS_MODULE,
},
在arch/arm/plat-s3c24xx/devs.c中定义了rtc的platform_device:
/* RTC */
static struct resource s3c_rtc_resource[] = { //定义了rtc平台设备会使用的资源
[0] = { //IO端口资源范围
.start = S3C24XX_PA_RTC,
.end = S3C24XX_PA_RTC + 0xff,
.flags = IORESOURCE_MEM,
[1] = { //RTC报警中断资源
.start = IRQ_RTC,
.end = IRQ_RTC,
.flags = IORESOURCE_IRQ,
[2] = { //TICK节拍时间中断资源
.start = IRQ_TICK,
.end = IRQ_TICK,
.flags = IORESOURCE_IRQ
struct platform_device s3c_device_rtc = { //定义了平台设备
.name = "s3c2410-rtc", //设备名
.id = -1,
.num_resources = ARRAY_SIZE(s3c_rtc_resource), //资源数量
.resource = s3c_rtc_resource, //引用上面定义的资源
平台驱动中定义了probe函数，下面来看他的实现：
static int __devinit s3c_rtc_probe(struct platform_device *pdev)
struct rtc_device *rtc;
struct resource *res;
int ret;
pr_debug("%s: probe=%p\n", __func__, pdev);
/* find the IRQs */
/*获得IRQ资源中的第二个，即TICK节拍时间中断号*/
s3c_rtc_tickno = platform_get_irq(pdev, 1);
if (s3c_rtc_tickno < 0) {
dev_err(&pdev->dev, "no irq for rtc tick\n");
return -ENOENT;
/*获取IRQ资源中的第一个，即RTC报警中断*/
s3c_rtc_alarmno = platform_get_irq(pdev, 0);
if (s3c_rtc_alarmno < 0) {
dev_err(&pdev->dev, "no irq for alarm\n");
pr_debug("s3c2410_rtc: tick irq %d, alarm irq %d\n",
s3c_rtc_tickno, s3c_rtc_alarmno);
/* get the memory region */
/*获取RTC平台设备所使用的IO端口资源*/
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (res == NULL) {
dev_err(&pdev->dev, "failed to get memory region resource\n");
/*申请IO端口资源所占用的IO空间*/
s3c_rtc_mem = request_mem_region(res->start,
res->end-res->start+1,
pdev->name);
if (s3c_rtc_mem == NULL) {
dev_err(&pdev->dev, "failed to reserve memory region\n");
ret = -ENOENT;
goto err_nores;
/*将IO端口占用的IO空间映射到虚拟地址，s3c_rtc_base是这段虚拟地址的起始地址*/
s3c_rtc_base = ioremap(res->start, res->end - res->start + 1);
if (s3c_rtc_base == NULL) {
dev_err(&pdev->dev, "failed ioremap()\n");
ret = -EINVAL;
goto err_nomap;
/* check to see if everything is setup correctly */
/*对RTCCON第0位进行操作，使能RTC*/
s3c_rtc_enable(pdev, 1);
pr_debug("s3c2410_rtc: RTCCON=%02x\n",
readb(s3c_rtc_base + S3C2410_RTCCON));
/*对TICNT第7位进行操作，使能节拍时间计数寄存器*/
s3c_rtc_setfreq(&pdev->dev, 1);
/*让电源管理支持唤醒功能*/
device_init_wakeup(&pdev->dev, 1);
/* register RTC and exit */
/*注册rtc设备，名为"s3c",与s3c_rtcops这个rtc_class_ops进行关联*/
rtc = rtc_device_register("s3c", &pdev->dev, &s3c_rtcops,
THIS_MODULE);
if (IS_ERR(rtc)) {
dev_err(&pdev->dev, "cannot attach rtc\n");
ret = PTR_ERR(rtc);
goto err_nortc;
/**/
rtc->max_user_freq = 128;
/*将rtc这个rtc_device存放在&pdev->dev->driver_data*/
platform_set_drvdata(pdev, rtc);
err_nortc:
s3c_rtc_enable(pdev, 0);
iounmap(s3c_rtc_base);
err_nomap:
release_resource(s3c_rtc_mem);
err_nores:
return ret;
函数rtc_device_register在文件class.c中实现:
struct rtc_device *rtc_device_register(const char *name, struct device *dev,
const struct rtc_class_ops *ops,
struct module *owner)
int id, err;
/*为idr(rtc_idr)分配内存*/
if (idr_pre_get(&rtc_idr, GFP_KERNEL) == 0) {
err = -ENOMEM;
goto exit;
mutex_lock(&idr_lock);
/*分配ID号存于id中，该ID号最终将作为该RTC设备的次设备号*/
err = idr_get_new(&rtc_idr, NULL, &id);
mutex_unlock(&idr_lock);
id = id & MAX_ID_MASK;
/*为RTC结构分配内存*/
rtc = kzalloc(sizeof(struct rtc_device), GFP_KERNEL);
if (rtc == NULL) {
goto exit_idr;
rtc->id = id;
/*指向原始操作函数集*/
rtc->ops = ops;
rtc->owner = owner;
rtc->max_user_freq = 64;
rtc->dev.parent = dev;
rtc->dev.class = rtc_class;
rtc->dev.release = rtc_device_release;
mutex_init(&rtc->ops_lock);
spin_lock_init(&rtc->irq_lock);
spin_lock_init(&rtc->irq_task_lock);
init_waitqueue_head(&rtc->irq_queue);
strlcpy(rtc->name, name, RTC_DEVICE_NAME_SIZE);
dev_set_name(&rtc->dev, "rtc%d", id);
/*rtc->dev.devt = MKDEV(MAJOR(rtc_devt),rtc->id); cdev_init(&rtc->char_dev,&rtc_dev_fops);其中rtc_devt是从调用alloc_chrdev_region时获得的*/
rtc_dev_prepare(rtc);
/*注册该RTC设备rtc->dev*/
err = device_register(&rtc->dev);
if (err)
goto exit_kfree;
/*cdev_add(&rtc->chr_dev,rtc->dev.devt,1);将rtc->chrdev注册到系统中*/
rtc_dev_add_device(rtc);
/*在/sys下添加属性文件*/
rtc_sysfs_add_device(rtc);
/*在/proc中创建入口项"driver/rtc"*/
rtc_proc_add_device(rtc);
dev_info(dev, "rtc core: registered %s as %s\n",
rtc->name, dev_name(&rtc->dev));
return rtc;
exit_kfree:
kfree(rtc);
exit_idr:
idr_remove(&rtc_idr, id);
exit:
dev_err(dev, "rtc core: unable to register %s, err = %d\n",
name, err);
return ERR_PTR(err);
下边是s3c_rtc_enable函数的实现：
static void s3c_rtc_enable(struct platform_device *pdev, int en)
void __iomem *base = s3c_rtc_base;
unsigned int tmp;
if (s3c_rtc_base == NULL)
return;
/*如果禁止，就disable RTCCON与TICNT*/
if (!en) {
tmp = readb(base + S3C2410_RTCCON);
writeb(tmp & ~S3C2410_RTCCON_RTCEN, base + S3C2410_RTCCON);
tmp = readb(base + S3C2410_TICNT);
writeb(tmp & ~S3C2410_TICNT_ENABLE, base + S3C2410_TICNT);
} else {
/* re-enable the device, and check it is ok */
/*如果RTCCON没有使能，则使能之*/
if ((readb(base+S3C2410_RTCCON) & S3C2410_RTCCON_RTCEN) == 0){
dev_info(&pdev->dev, "rtc disabled, re-enabling\n");
tmp = readb(base + S3C2410_RTCCON);
writeb(tmp|S3C2410_RTCCON_RTCEN, base+S3C2410_RTCCON);
}
/*如果BCD的计数选择位为1，则置位0，即Merge BCD counts*/
if ((readb(base + S3C2410_RTCCON) & S3C2410_RTCCON_CNTSEL)){
dev_info(&pdev->dev, "removing RTCCON_CNTSEL\n");
writeb(tmp& ~S3C2410_RTCCON_CNTSEL, base+S3C2410_RTCCON);
/*如果BCD的时钟选择为1，则置位0，即XTAL 1/215 divided clock*/
if ((readb(base + S3C2410_RTCCON) & S3C2410_RTCCON_CLKRST)){
dev_info(&pdev->dev, "removing RTCCON_CLKRST\n");
writeb(tmp & ~S3C2410_RTCCON_CLKRST, base+S3C2410_RTCCON);
static int __devexit s3c_rtc_remove(struct platform_device *dev)
/*从系统平台设备中获取RTC设备类的数据*/
struct rtc_device *rtc = platform_get_drvdata(dev);
/*清空平台设备中RTC驱动数据*/
platform_set_drvdata(dev, NULL);
/*注销RTC设备类*/
rtc_device_unregister(rtc);
/*禁止RTC节拍时间计数寄存器TICNT的使能功能*/
s3c_rtc_setpie(&dev->dev, 0);
/*禁止RTC报警控制寄存器RTCALM的全局报警使能功能*/
s3c_rtc_setaie(0);
/*释放RTC虚拟地址映射空间*/
/*释放获取的RTC平台设备的资源*/
/*销毁保存RTC平台设备的资源内存空间*/
kfree(s3c_rtc_mem);
这里是电源管理部分，在挂起时保存TICNT的值，并禁止RTCCON，TICNT；在休眠的时候开启RTCCON，并恢复TICNT的值。
#ifdef CONFIG_PM
/* RTC Power management control */
static int ticnt_save;
static int s3c_rtc_suspend(struct platform_device *pdev, pm_message_t state)
/* save TICNT for anyone using periodic interrupts */
ticnt_save = readb(s3c_rtc_base + S3C2410_TICNT);
static int s3c_rtc_resume(struct platform_device *pdev)
writeb(ticnt_save, s3c_rtc_base + S3C2410_TICNT);
#else
#define s3c_rtc_suspend NULL
#define s3c_rtc_resume NULL
s3c_rtcops是RTC设备在RTC核心部分注册的对RTC设备进行操作的结构体，类似字符设备在驱动中的file_operations对字符设备进行操作的意思。
static const struct rtc_class_ops s3c_rtcops = {
.open = s3c_rtc_open,
.release = s3c_rtc_release,
.read_time = s3c_rtc_gettime,
.set_time = s3c_rtc_settime,
.read_alarm = s3c_rtc_getalarm,
.set_alarm = s3c_rtc_setalarm,
.irq_set_freq = s3c_rtc_setfreq,
.irq_set_state = s3c_rtc_setpie,
.proc = s3c_rtc_proc,
这两个是下边会用到的中断处理函数，产生一个时钟中断的时候就更新一下rtc_irq_data的值，也就是说只有当产生一个时钟中断(也就是一个滴答tick)才返回给用户一个时间。
static irqreturn_t s3c_rtc_alarmirq(int irq, void *id)
struct rtc_device *rdev = id;
rtc_update_irq(rdev, 1, RTC_AF | RTC_IRQF);
return IRQ_HANDLED;
static irqreturn_t s3c_rtc_tickirq(int irq, void *id)
rtc_update_irq(rdev, 1, RTC_PF | RTC_IRQF);
首先来看打开和关闭函数：
static int s3c_rtc_open(struct device *dev)
/*获得平台设备，从平台设备pdev->dev->driver_data获取rtc_device*/
struct platform_device *pdev = to_platform_device(dev);
struct rtc_device *rtc_dev = platform_get_drvdata(pdev);
/*注册RTC报警中断的中断处理函数*/
ret = request_irq(s3c_rtc_alarmno, s3c_rtc_alarmirq,
IRQF_DISABLED, "s3c2410-rtc alarm", rtc_dev);
if (ret) {
dev_err(dev, "IRQ%d error %d\n", s3c_rtc_alarmno, ret);
return ret;
/*注册TICK节拍时间中断的中断处理函数*/
ret = request_irq(s3c_rtc_tickno, s3c_rtc_tickirq,
IRQF_DISABLED, "s3c2410-rtc tick", rtc_dev);
dev_err(dev, "IRQ%d error %d\n", s3c_rtc_tickno, ret);
goto tick_err;
tick_err:
free_irq(s3c_rtc_alarmno, rtc_dev);
RTC设备类关闭接口函数：
static void s3c_rtc_release(struct device *dev)
{
/* do not clear AIE here, it may be needed for wake */
s3c_rtc_setpie(dev, 0);
free_irq(s3c_rtc_tickno, rtc_dev);
更新RTCALM寄存器的状态，是否使能：
static void s3c_rtc_setaie(int to)
pr_debug("%s: aie=%d\n", __func__, to);
tmp = readb(s3c_rtc_base + S3C2410_RTCALM) & ~S3C2410_RTCALM_ALMEN;
if (to)
tmp |= S3C2410_RTCALM_ALMEN;
writeb(tmp, s3c_rtc_base + S3C2410_RTCALM);
更新TICNT寄存器的状态，是否使能：
static int s3c_rtc_setpie(struct device *dev, int enabled)
pr_debug("%s: pie=%d\n", __func__, enabled);
spin_lock_irq(&s3c_rtc_pie_lock);
tmp = readb(s3c_rtc_base + S3C2410_TICNT) & ~S3C2410_TICNT_ENABLE;
if (enabled)
tmp |= S3C2410_TICNT_ENABLE;
writeb(tmp, s3c_rtc_base + S3C2410_TICNT);
spin_unlock_irq(&s3c_rtc_pie_lock);
更新TICNT节拍时间计数的值：
static int s3c_rtc_setfreq(struct device *dev, int freq)
if (!is_power_of_2(freq))
return -EINVAL;
tmp = readb(s3c_rtc_base + S3C2410_TICNT) & S3C2410_TICNT_ENABLE;
tmp |= (128 / freq)-1;
/* Time read/write */
static int s3c_rtc_gettime(struct device *dev, struct rtc_time *rtc_tm)
unsigned int have_retried = 0;
/*获得rtc IO端口寄存器的虚拟地址的起始地址*/
retry_get_time:
/*读取RTC中BCD数中的：分、时、日期、月、年、秒，放到rtc_time rtc_tm中*/
rtc_tm->tm_min = readb(base + S3C2410_RTCMIN);
rtc_tm->tm_hour = readb(base + S3C2410_RTCHOUR);
rtc_tm->tm_mday = readb(base + S3C2410_RTCDATE);
rtc_tm->tm_mon = readb(base + S3C2410_RTCMON);
rtc_tm->tm_year = readb(base + S3C2410_RTCYEAR);
rtc_tm->tm_sec = readb(base + S3C2410_RTCSEC);
/* the only way to work out wether the system was mid-update
* when we read it is to check the second counter, and if it
* is zero, then we re-try the entire read
*/
/*如果到达0秒就检查一下，因为年月日时分可能会有加1操作，比如此时是一年的最后天的最后一分一秒，则年月日时分秒都会改变*/
if (rtc_tm->tm_sec == 0 && !have_retried) {
have_retried = 1;
goto retry_get_time;
pr_debug("read time %02x.%02x.%02x %02x/%02x/%02x\n",
rtc_tm->tm_year, rtc_tm->tm_mon, rtc_tm->tm_mday,
rtc_tm->tm_hour, rtc_tm->tm_min, rtc_tm->tm_sec);
/*使用readb读取寄存器的值得到的是bcd格式，必须转换成bin格式再保存*/
rtc_tm->tm_sec = bcd2bin(rtc_tm->tm_sec);
rtc_tm->tm_min = bcd2bin(rtc_tm->tm_min);
rtc_tm->tm_hour = bcd2bin(rtc_tm->tm_hour);
rtc_tm->tm_mday = bcd2bin(rtc_tm->tm_mday);
rtc_tm->tm_mon = bcd2bin(rtc_tm->tm_mon);
rtc_tm->tm_year = bcd2bin(rtc_tm->tm_year);
rtc_tm->tm_year += 100;
rtc_tm->tm_mon -= 1;
static int s3c_rtc_settime(struct device *dev, struct rtc_time *tm)
int year = tm->tm_year - 100;
pr_debug("set time %02d.%02d.%02d %02d/%02d/%02d\n",
tm->tm_year, tm->tm_mon, tm->tm_mday,
tm->tm_hour, tm->tm_min, tm->tm_sec);
/* we get around y2k by simply not supporting it */
/*RTC时钟的范围是00~99，由BCDYEAR寄存器的0～7位存储*/
if (year < 0 || year >= 100) {
dev_err(dev, "rtc only supports 100 years\n");
/*将上面保存到RTC核心定义的时间结构体中的时间日期值写入对应的寄存器中*/
writeb(bin2bcd(tm->tm_sec), base + S3C2410_RTCSEC);
writeb(bin2bcd(tm->tm_min), base + S3C2410_RTCMIN);
writeb(bin2bcd(tm->tm_hour), base + S3C2410_RTCHOUR);
writeb(bin2bcd(tm->tm_mday), base + S3C2410_RTCDATE);
writeb(bin2bcd(tm->tm_mon + 1), base + S3C2410_RTCMON);
writeb(bin2bcd(year), base + S3C2410_RTCYEAR);
获取报警时间的值：
static int s3c_rtc_getalarm(struct device *dev, struct rtc_wkalrm *alrm)
struct rtc_time *alm_tm = &alrm->time;
unsigned int alm_en;
/*从RTC的报警寄存器中读取*/
alm_tm->tm_sec = readb(base + S3C2410_ALMSEC);
alm_tm->tm_min = readb(base + S3C2410_ALMMIN);
alm_tm->tm_hour = readb(base + S3C2410_ALMHOUR);
alm_tm->tm_mon = readb(base + S3C2410_ALMMON);
alm_tm->tm_mday = readb(base + S3C2410_ALMDATE);
alm_tm->tm_year = readb(base + S3C2410_ALMYEAR);
alm_en = readb(base + S3C2410_RTCALM);
/*根据RTCALM寄存器的报警全局使能位来设置报警状态结构rtc_wkalrm*/
alrm->enabled = (alm_en & S3C2410_RTCALM_ALMEN) ? 1 : 0;
pr_debug("read alarm %02x %02x.%02x.%02x %02x/%02x/%02x\n",
alm_en,
alm_tm->tm_year, alm_tm->tm_mon, alm_tm->tm_mday,
alm_tm->tm_hour, alm_tm->tm_min, alm_tm->tm_sec);
/* decode the alarm enable field */
/*如果RTCALM寄存器的秒使能，则将rtc_wkalrm中存放的秒数据由BCD格式转换为BIN格式，否则设置为0xff*/
if (alm_en & S3C2410_RTCALM_SECEN)
alm_tm->tm_sec = bcd2bin(alm_tm->tm_sec);
else
alm_tm->tm_sec = 0xff;
/*如果RTCALM寄存器的分钟使能，则将rtc_wkalrm中存放的分钟数据由BCD格式转换为BIN格式，否则设置为0xff*/
if (alm_en & S3C2410_RTCALM_MINEN)
alm_tm->tm_min = bcd2bin(alm_tm->tm_min);
alm_tm->tm_min = 0xff;
/*如果RTCALM寄存器的小时使能，则将rtc_wkalrm中存放的小时数据由BCD格式转换为BIN格式，否则设置为0xff*/
if (alm_en & S3C2410_RTCALM_HOUREN)
alm_tm->tm_hour = bcd2bin(alm_tm->tm_hour);
alm_tm->tm_hour = 0xff;
/*如果RTCALM寄存器的日使能，则将rtc_wkalrm中存放的日数据由BCD格式转换为BIN格式，否则设置为0xff*/
if (alm_en & S3C2410_RTCALM_DAYEN)
alm_tm->tm_mday = bcd2bin(alm_tm->tm_mday);
alm_tm->tm_mday = 0xff;
/*如果RTCALM寄存器的月使能，则将rtc_wkalrm中存放的月数据由BCD格式转换为BIN格式，否则设置为0xff*/
if (alm_en & S3C2410_RTCALM_MONEN) {
alm_tm->tm_mon = bcd2bin(alm_tm->tm_mon);
alm_tm->tm_mon -= 1;
alm_tm->tm_mon = 0xff;
/*如果RTCALM寄存器的年使能，则将rtc_wkalrm中存放的年数据由BCD格式转换为BIN格式，否则设置为0xff*/
if (alm_en & S3C2410_RTCALM_YEAREN)
alm_tm->tm_year = bcd2bin(alm_tm->tm_year);
alm_tm->tm_year = 0xffff;
设置报警时间的值：
static int s3c_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
struct rtc_time *tm = &alrm->time;
unsigned int alrm_en;
pr_debug("s3c_rtc_setalarm: %d, %02x/%02x/%02x %02x.%02x.%02x\n",
alrm->enabled,
tm->tm_mday & 0xff, tm->tm_mon & 0xff, tm->tm_year & 0xff,
tm->tm_hour & 0xff, tm->tm_min & 0xff, tm->tm_sec);
/*读取RTCALM寄存器的全局使能位，关闭所有报警使能*/
alrm_en = readb(base + S3C2410_RTCALM) & S3C2410_RTCALM_ALMEN;
writeb(0x00, base + S3C2410_RTCALM);
/*如果秒时间在合理范围内，则使能秒报警位，将报警状态寄存器中封装的time的秒位由BIN格式转换为BCD，写入秒报警寄存器中*/
if (tm->tm_sec < 60 && tm->tm_sec >= 0) {
alrm_en |= S3C2410_RTCALM_SECEN;
writeb(bin2bcd(tm->tm_sec), base + S3C2410_ALMSEC);
/*如果分钟时间在合理范围内，则使能分钟报警位，将报警状态寄存器中封装的time的分钟位由BIN格式转换为BCD，写入分钟报警寄存器中*/
if (tm->tm_min < 60 && tm->tm_min >= 0) {
alrm_en |= S3C2410_RTCALM_MINEN;
writeb(bin2bcd(tm->tm_min), base + S3C2410_ALMMIN);
/*如果小时时间在合理范围内，则使能小时报警位，将报警状态寄存器中封装的time的小时位由BIN格式转换为BCD，写入小时报警寄存器中*/
if (tm->tm_hour < 24 && tm->tm_hour >= 0) {
alrm_en |= S3C2410_RTCALM_HOUREN;
writeb(bin2bcd(tm->tm_hour), base + S3C2410_ALMHOUR);
pr_debug("setting S3C2410_RTCALM to %08x\n", alrm_en);
/*使能RTCALM寄存器全局报警位*/
writeb(alrm_en, base + S3C2410_RTCALM);
s3c_rtc_setaie(alrm->enabled);
/*根据全局报警使能的状态来决定是唤醒RTC报警中断还是睡眠RTC报警中断*/
if (alrm->enabled)
enable_irq_wake(s3c_rtc_alarmno);
disable_irq_wake(s3c_rtc_alarmno);
下面来分析一下是怎样获取和设置时间的：
通过用户空间的ioctl，在rtc-dev.c中实现了rtc_dev_ioctl，其中获取和设置时间如下：
case RTC_RD_TIME:
mutex_unlock(&rtc->ops_lock);
err = rtc_read_time(rtc, &tm);
if (err < 0)
return err;
if (copy_to_user(uarg, &tm, sizeof(tm)))
err = -EFAULT;
return err;
case RTC_SET_TIME:
if (copy_from_user(&tm, uarg, sizeof(tm)))
return -EFAULT;
return rtc_set_time(rtc, &tm);
通过copy_to_user和copy_from_user实现时间在内核空间与用户空间的传递。这里调用到的rtc_read_time和rtc_set_time在interface.c中实现：
int rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm)
err = mutex_lock_interruptible(&rtc->ops_lock);
if (!rtc->ops)
err = -ENODEV;
else if (!rtc->ops->read_time)
err = -EINVAL;
else {
memset(tm, 0, sizeof(struct rtc_time));
err = rtc->ops->read_time(rtc->dev.parent, tm);
mutex_unlock(&rtc->ops_lock);
return err;
int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
err = rtc_valid_tm(tm);
if (err != 0)
else if (rtc->ops->set_time)
err = rtc->ops->set_time(rtc->dev.parent, tm);
else if (rtc->ops->set_mmss) {
unsigned long secs;
err = rtc_tm_to_time(tm, &secs);
if (err == 0)
err = rtc->ops->set_mmss(rtc->dev.parent, secs);
} else
可以看出他们调用了具体RTC设备驱动中的read_time和set_time函数，对应了s3c2410中的s3c_rtc_gettime和s3c_rtc_settime,这里使用的rtc_tm_to_time函数实现在rtclib.c中，/drivers/rtc/interface.c定义了可供其它模块访问的接口。
本文转自张昺华-sky博客园博客，原文链接：http://www.cnblogs.com/sky-heaven/p/5294484.html，如需转载请自行联系原作者
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