UM0851 datasheet(40/245 Pages) STMICROELECTRONICS

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Platform section

UM0851

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Doc ID 16604 Rev 2

Figure 6.

RTC software system architecture

Note:

To get access to the real time clock, you need to create a character special file /dev/rtc with

major number 10 and minor number 135.

An "RTC Class" framework is defined to support several different RTCs. It offers three

different user space interfaces:

●

/dev/rtcN … much the same as the older /dev/rtc interface.

●

/sys/class/rtc/rtcN … sysfs attributes support read-only access to some RTC attributes.

●

/proc/driver/rtc … the first RTC (rtc0) may expose itself using a proc-fs interface.

The kernel has a dedicated RTC subsystem providing the top-layer char driver and a core

infrastructure that bottom-layer RTC drivers can use to tie in with the top layer. The main

components of this infrastructure are the rtc_class_ops structure and the registration

functions, rtc_device_[register|unregister](). Bottom-layer RTC drivers scattered under

different bus-specific directories are unified with this subsystem under drivers/rtc/.

Linux RTC class interface

struct rtc_class_ops {

struct module *owner;

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);

};

rtc = rtc_device_register(pdev->name, &pdev->dev,

hwclock

/dev/rtc

Linux RTC Class

RTC driver

RTC hardware

Hardware

Kernel space

User space

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