Linux Device Drivers Development

The sysfs interface

The kernel code responsible for instantiating RTC attributes in sysfs is defined in drivers/rtc/rtc-sysfs.c, in the kernel source tree. Once registered, an RTC device will create a rtc<id> directory under /sys/class/rtc. That directory contains a set of read-only attributes, the most important of which are:

• date: This file prints the current date of the RTC interface:

$ cat /sys/class/rtc/rtc0/date
2017-08-28  

• time: This prints the current time of the RTC:

    $ cat /sys/class/rtc/rtc0/time
    14:54:20  

• hctosys: This attribute indicates whether the RTC device is the one specified in CONFIG_RTC_HCTOSYS_DEVICE, meaning that this RTC is used to set the system time on startup and resume. Read 1 as true, and 0 as false:

 $ ...