1.系统时间(WT):
由Linux系统软件维持的时间,通过Linux命令date查看:
rk3568_r:/
Wed Sep 21 03:05:21 GMT 2022
获取到的就是系统时间
2.RTC时间:
这个时间来自我们设备上的RTC芯片,通过Linux命令hwclock 可以读取:
rk3568_r:/
Wed Sep 21 03:05:24 2022 0.000000 seconds
我们通过man查看date和hwclock的介绍:
命令说明
1)date
DESCRIPTION
Display the current time in the given FORMAT, or set the system date.
2)hwclock
DESCRIPTION
hwclock is a tool for accessing the Hardware Clock. It can: display the Hardware
Clock time; set the Hardware Clock to a specified time; set the Hardware Clock from
the System Clock; set the System Clock from the Hardware Clock; compensate for
Hardware Clock drift; correct the System Clock timescale; set the kernel's time‐
zone, NTP timescale, and epoch (Alpha only); compare the System and Hardware
Clocks; and predict future Hardware Clock values based on its drift rate.
Since v2.26 important changes were made to the --hctosys function and the --direc‐
tisa option, and a new option --update-drift was added. See their respective
descriptions below.
接下来,通过代码看下两者的关系。
二、RTC时间框架
框架如图:
从该架构可得:
Hardware:提供时间信息(time&alarm),通过一定的接口(比如I2C)和RTC Driver进行交互
Driver: 完成硬件的访问功能,提供访问接口,以驱动的形式驻留在系统
class.c:驱动注册方式由class.c:文件提供。驱动注册成功后会构建rtc_device结构体表征的rtc设备,并把rtc芯片的操作方式存放到rtc设备的ops成员中
interface.c:文件屏蔽硬件相关的细节,向上提供统一的获取/设置时间或Alarm的接口
rtc-lib.c:文件提供通用的时间操作函数,如rtc_time_to_tm、rtc_valid_tm等
rtc-dev.c:文件在/dev/目录下创建设备节点供应用层访问,如open、read、ioctl等,访问方式填充到file_operations结构体中
hctosys.c/rtc-sys.c/rtc-proc.c:将硬件时钟写给 wall time
下面我们从底层往上层来一步步分析。
1、rtc_class_ops 填充
驱动主要工作是填充 rtc_class_ops结构体,结构体描述了RTC芯片能够提供的所有操作方式:
struct rtc_class_ops {
int (*open)(struct device *);
void (*release)(struct device *);
int (*ioctl)(struct device *, unsigned int, unsigned long);
int (*read_time)(struct device *, struct rtc_time *);
int (*set_time)(struct device *, struct rtc_time *);
int (*read_alarm)(struct device *, struct rtc_wkalrm *);
int (*set_alarm)(struct device *, struct rtc_wkalrm *);
int (*proc)(struct device *, struct seq_file *);
int (*set_mmss)(struct device *, unsigned long secs);
int (*read_callback)(struct device *, int data);
int (*alarm_irq_enable)(struct device *, unsigned int enabled);
};
实现:
static const struct rtc_class_ops hym8563_rtc_ops = {
.read_time = hym8563_rtc_read_time,
.set_time = hym8563_rtc_set_time,
.alarm_irq_enable = hym8563_rtc_alarm_irq_enable,
.read_alarm = hym8563_rtc_read_alarm,
.set_alarm = hym8563_rtc_set_alarm,
};
注册:
hym8563->rtc = devm_rtc_device_register(&client->dev, client->name,
&hym8563_rtc_ops, THIS_MODULE);
成功的话log:
[ 0.758774] hym8563_probe()---565----
[ 0.760651] rtc-hym8563 5-0051: rtc information is invalid
[ 0.761666] hym8563_rtc_read_time()---115----1--
[ 0.761681] hym8563_rtc_set_time()---129----1--
[ 0.764235] hym8563_rtc_read_time()---115----1--
[ 0.766425] hym8563_rtc_read_time()---115----1--
[ 0.767439] hym8563_rtc_read_time()---115----1--
[ 0.767619] rtc-hym8563 5-0051: rtc core: registered hym8563 as rtc0
[ 0.768634] hym8563_rtc_read_time()---115----1--
[ 0.768661] rtc-hym8563 5-0051: setting system clock to 2021-01-01 12:00:00 UTC (1609502400)
从log可得 5-0051: 5表示I2C通道5,0051表示从设备地址 rtc0 :注册的rtc设备为rtc0。
2、class.c和RTC驱动注册
class.c文件在RTC驱动注册之前开始得到运行:
static int __init rtc_init(void)
{
rtc_class = class_create(THIS_MODULE, "rtc");
rtc_class->suspend = rtc_suspend;
rtc_class->resume = rtc_resume;
rtc_dev_init();
rtc_sysfs_init(rtc_class);
return 0;
}
subsys_initcall(rtc_init);
函数功能:
- 创建名为rtc的class
- 提供PM相关接口suspend/resume
- rtc_dev_init():动态申请/dev/rtcN的设备号
- rtc_sysfs_init():rtc类具有的device_attribute属性
3、RTC驱动注册函数devm_rtc_device_register():
drivers/class.c
struct rtc_device *devm_rtc_device_register(struct device *dev,
const char *name,
const struct rtc_class_ops *ops,
struct module *owner)
{
struct rtc_device **ptr, *rtc;
ptr = devres_alloc(devm_rtc_device_release, sizeof(*ptr), GFP_KERNEL);
if (!ptr)
return ERR_PTR(-ENOMEM);
rtc = rtc_device_register(name, dev, ops, owner);
if (!IS_ERR(rtc)) {
*ptr = rtc;
devres_add(dev, ptr);
} else {
devres_free(ptr);
}
return rtc;
}
rtc_device_register()定义如下:
struct rtc_device *rtc_device_register(const char *name, struct device *dev,
const struct rtc_class_ops *ops,
struct module *owner)
{
struct rtc_device *rtc;
struct rtc_wkalrm alrm;
int id, err;
id = ida_simple_get(&rtc_ida, 0, 0, GFP_KERNEL);
rtc = kzalloc(sizeof(struct rtc_device), GFP_KERNEL);
rtc->id = id;
rtc->ops = ops;
rtc->owner = owner;
rtc->irq_freq = 1;
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);
timerqueue_init_head(&rtc->timerqueue);
INIT_WORK(&rtc->irqwork, rtc_timer_do_work);
rtc_timer_init(&rtc->aie_timer, rtc_aie_update_irq, (void *)rtc);
rtc_timer_init(&rtc->uie_rtctimer, rtc_uie_update_irq, (void *)rtc);
hrtimer_init(&rtc->pie_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
rtc->pie_timer.function = rtc_pie_update_irq;
rtc->pie_enabled = 0;
err = __rtc_read_alarm(rtc, &alrm);
if (!err && !rtc_valid_tm(&alrm.time))
rtc_initialize_alarm(rtc, &alrm);
strlcpy(rtc->name, name, RTC_DEVICE_NAME_SIZE);
dev_set_name(&rtc->dev, "rtc%d", id);
rtc_dev_prepare(rtc);
err = device_register(&rtc->dev);
rtc_dev_add_device(rtc);
rtc_sysfs_add_device(rtc);
rtc_proc_add_device(rtc);
dev_info(dev, "rtc core: registered %s as %s\n",
rtc->name, dev_name(&rtc->dev));
return rtc;
}
有了 /dev/rtc0后,应用层就可以通过 open/read/ioctl操作RTC设备了,对应与内核的file_operations:
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,
};
4、硬件抽象层interface.c
硬件抽象,即屏蔽具体的硬件细节,为上层用户提供统一的调用接口,使用者无需关心这些接口是怎么实现的。 以RTC访问为例,抽象的实现位于interface.c文件,其实现基于class.c中创建的rtc_device设备。 实现原理,以rtc_set_time为例:
drivers/interface.c
int rtc_set_time(struct rtc_device *rtc, struct rtc_time *tm)
{
int err;
err = rtc_valid_tm(tm);
err = mutex_lock_interruptible(&rtc->ops_lock);
if (err)
return err;
if (!rtc->ops)
err = -ENODEV;
else if (rtc->ops->set_time)
err = rtc->ops->set_time(rtc->dev.parent, tm);
mutex_unlock(&rtc->ops_lock);
schedule_work(&rtc->irqwork);
return err;
}
5、rtc在sysfs文件系统中的呈现
之前曾建立过名为rtc的class:
rtc_class = class_create(THIS_MODULE, "rtc");
查看之:
# ls /sys/class/rtc/
rtc0
# ls -l /sys/class/rtc/
lrwxrwxrwx 1 root root 0 2021-01-01 12:00 rtc0 -> ../../devices/platform/fe5e0000.i2c/i2c-5/5-0051/rtc/rtc0
我们系统中只有一个RTC,所以编号为rtc0。
同时发现rtc0文件为指向/sys/devices/platform/fe5e0000.i2c/i2c-5/5-0051/rtc/rtc0的符号链接,
RTC芯片是I2C接口,所以rtc0挂载在I2C的总线上,总线控制器地址fe5e0000,控制器编号为5,RTC芯片作为slave端地址为0x51。
rtc0 设备属性:
drivers/rtc-sysfs.c
void __init rtc_sysfs_init(struct class *rtc_class)
{
rtc_class->dev_attrs = rtc_attrs;
}
static struct attribute *rtc_attrs[] = {
&dev_attr_name.attr,
&dev_attr_date.attr,
&dev_attr_time.attr,
&dev_attr_since_epoch.attr,
&dev_attr_max_user_freq.attr,
&dev_attr_hctosys.attr,
NULL,
};
对应文件系统中的文件节点:
rk3568_r:/sys/class/rtc # cd rtc0/
rk3568_r:/sys/class/rtc/rtc0 # ls -l
total 0
-r--r--r-- 1 root root 4096 2022-09-21 03:56 date
-r--r--r-- 1 root root 4096 2022-09-21 03:56 dev
lrwxrwxrwx 1 root root 0 2022-09-21 03:56 device -> ../../../5-0051
-r--r--r-- 1 root root 4096 2021-01-01 12:00 hctosys
-rw-r--r-- 1 root root 4096 2022-09-21 03:56 max_user_freq
-r--r--r-- 1 root root 4096 2022-09-21 03:56 name
drwxr-xr-x 2 root root 0 2021-01-01 12:00 power
-r--r--r-- 1 root root 4096 2022-09-21 03:56 since_epoch
lrwxrwxrwx 1 root root 0 2022-09-21 03:56 subsystem -> ../../../../../../../class/rtc
-r--r--r-- 1 root root 4096 2022-09-21 03:56 time
-rw-r--r-- 1 root root 4096 2021-01-01 12:00 uevent
-rw-r--r-- 1 root root 4096 2022-09-21 03:56 wakealarm
drwxr-xr-x 2 root root 0 2021-01-01 12:00 wakeup8
6、rtc在proc文件系统中的呈现
之前曾rtc0设备加入到了/proc
drivers/class.c
rtc_device_register()
{
--->rtc_proc_add_device(rtc);
}
void rtc_proc_add_device(struct rtc_device *rtc)
{
if (is_rtc_hctosys(rtc))
proc_create_data("driver/rtc", 0, NULL, &rtc_proc_fops, rtc);
}
查看之:
# cat /proc/driver/rtc
rtc_time : 03:59:11
rtc_date : 2022-09-21
alrm_time : 12:00:00
alrm_date : 2021-01-02
alarm_IRQ : no
alrm_pending : no
update IRQ enabled : no
periodic IRQ enabled : no
periodic IRQ frequency : 1
max user IRQ frequency : 64
24hr : yes
信息来源:
rtc_proc_fops
-->rtc_proc_open
-->rtc_proc_show
三、WT时间和RTC时间同步问题
1.WT时间来自于RTC时间,流程是:
上电-->RTC驱动加载-->从RTC同步时间到WT时间
对应驱动代码:
hctosys.c (drivers\rtc)
static int __init rtc_hctosys(void)
{
......
struct timespec tv = {
.tv_nsec = NSEC_PER_SEC >> 1,
};
err = rtc_read_time(rtc, &tm);
err = do_settimeofday(&tv);
dev_info(rtc->dev.parent,
"setting system clock to "
"%d-%02d-%02d %02d:%02d:%02d UTC (%u)\n",
tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
tm.tm_hour, tm.tm_min, tm.tm_sec,
(unsigned int) tv.tv_sec);
......
}
late_initcall(rtc_hctosys);
late_initcall说明系统在启动流程的后面才会调用该函数去同步时间。
2.瑞芯微时间操作
在瑞芯微的系统中,安卓部分程序其实最终也是依赖**/sys/class/rtc/rtc0** 下的文件节点实现时间管理功能的。
安卓程序会通过AlarmImpl::getTime、AlarmImpl::setTime()方法来获得和设置RTC时间:
frameworks/base/services/core/jni/com_android_server_AlarmManagerService.cpp
122 int AlarmImpl::getTime(int type, struct itimerspec *spec)
123 {
124 if (static_cast<size_t>(type) > ANDROID_ALARM_TYPE_COUNT) {
125 errno = EINVAL;
126 return -1;
127 }
128
129 return timerfd_gettime(fds[type], spec);
130 }
131
132 int AlarmImpl::setTime(struct timeval *tv)
133 {
134 struct rtc_time rtc;
135 struct tm tm, *gmtime_res;
136 int fd;
137 int res;
138
139 res = settimeofday(tv, NULL);
140 if (res < 0) {
141 ALOGV("settimeofday() failed: %s\n", strerror(errno));
142 return -1;
143 }
144
145 if (rtc_id < 0) {
146 ALOGV("Not setting RTC because wall clock RTC was not found");
147 errno = ENODEV;
148 return -1;
149 }
150
151 android::String8 rtc_dev = String8::format("/dev/rtc%d", rtc_id);
152 fd = open(rtc_dev.string(), O_RDWR);
153 if (fd < 0) {
154 ALOGV("Unable to open %s: %s\n", rtc_dev.string(), strerror(errno));
155 return res;
156 }
157
158 gmtime_res = gmtime_r(&tv->tv_sec, &tm);
159 if (!gmtime_res) {
160 ALOGV("gmtime_r() failed: %s\n", strerror(errno));
161 res = -1;
162 goto done;
163 }
164
165 memset(&rtc, 0, sizeof(rtc));
166 rtc.tm_sec = tm.tm_sec;
167 rtc.tm_min = tm.tm_min;
168 rtc.tm_hour = tm.tm_hour;
169 rtc.tm_mday = tm.tm_mday;
170 rtc.tm_mon = tm.tm_mon;
171 rtc.tm_year = tm.tm_year;
172 rtc.tm_wday = tm.tm_wday;
173 rtc.tm_yday = tm.tm_yday;
174 rtc.tm_isdst = tm.tm_isdst;
175 res = ioctl(fd, RTC_SET_TIME, &rtc);
176 if (res < 0)
177 ALOGV("RTC_SET_TIME ioctl failed: %s\n", strerror(errno));
178 done:
179 close(fd);
180 return res;
181 }
系统上电后,会先读取文件hctosys中的值,来决定是否将RTC时间写入到wall time:
255 static const char rtc_sysfs[] = "/sys/class/rtc";
256
257 static bool rtc_is_hctosys(unsigned int rtc_id)
258 {
259 android::String8 hctosys_path = String8::format("%s/rtc%u/hctosys",
260 rtc_sysfs, rtc_id);
261 FILE *file = fopen(hctosys_path.string(), "re");
262 if (!file) {
263 ALOGE("failed to open %s: %s", hctosys_path.string(), strerror(errno));
264 return false;
265 }
266
267 unsigned int hctosys;
268 bool ret = false;
269 int err = fscanf(file, "%u", &hctosys);
270 if (err == EOF)
271 ALOGE("failed to read from %s: %s", hctosys_path.string(),
272 strerror(errno));
273 else if (err == 0)
274 ALOGE("%s did not have expected contents", hctosys_path.string());
275 else
276 ret = hctosys;
277
278 fclose(file);
279 return ret;
280 }
269行,就是读取文件hctosys中的值,值为1则允许rtc时间写入到wall time,为0或者其他错误则不允许。
因为rtc只要有纽扣电池供电,就会有计时功能,
这是就是为什么,我们的设备关机并重启后,仍然能够显示正确的时间的原因。
【注意目录/sys/class/rtc/下文件是需要有访问权限的】
瑞芯微对文件权限的控制由以下文件提供:
device/rockchip/common/sepolicy/vendor/genfs_contexts
只需要按照对应的格式增加对应文件信息即可。