Architecture

The RTC driver follows Linux RTC subsystem. The RTC subsystem architecture is illustrated in figure below.

RTC subsystem architecture

The RTC is used to track wall time. It still works when system is in low power mode.

The RTC device is a standard character device. User space application can access RTC device through functions such as open, release, read, write and IOCTL. Also, RTC core provide APIs so kernel program can access it.

The RTC core provides 3 user space interfaces: /dev/rtc0, /proc/rtc, /sys/class/rtc/rtc0.

Implementation

The RTC driver is implemented as following files:

Driver location	Introduction
<linux>/drivers/rtkdrivers/rtc/Kconfig	RTC driver Kconfig
<linux>/drivers/rtkdrivers/rtc/Makefile	RTC driver Makefile
<linux>/drivers/rtkdrivers/rtc/rtk-rtc.c	RTC driver code

Configuration

DTS Configuration

The DTS node is defined in <dts>/rtl8730e-ocp.dtsi.

rtc: rtc@4200E000 {
   compatible = "realtek,ameba-rtc";
   reg = <0x4200E000 0x1000>;
   interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
   clocks = <&rcc RTK_CKE_RTC>;
};

The following table is property description.

Property	Description	Configurable?
compatible	ID to match the driver and device	No
reg	Register resource.	No
interrupts	SPI interrupt	No
clocks	RTC clock node	No

Build Configuration

Select Device Drivers > Drivers for Realtek > RTC driver:

APIs

APIs for User Space

The RTC subsystem provides 3 userspace interfaces:

• /dev/rtc0: RTC device.

• /sys/class/rtc/rtc0: Sysfs attributes support readonly access to some RTC attributes.

• /proc/driver/rtc: Procfs interface using for system clock RTC to expose itself.

User can access attributes to control RTC device via sysfs node. Below are some examples.

• Command to get RTC date (year, month, day):

  cat /sys/class/rtc/rtc0/date
  

• Command to get RTC time (hour, minute, second):

  cat /sys/class/rtc/rtc0/time
  

Refer to <sdk>/sources/kernel/<linux>/drivers/rtc/sysfs.c to get more information about sysfs interface.

Refer to RTC Drivers for Linux to get more information.

The RTC device acts as a character device. User can use open, read, ioctl, etc. to access RTC device. Refer to <test>/rtc for test demo.

APIs for Kernel Space

Interfaces	Introduction
rtc_class_open	Open RTC device
rtc_class_close	Close RTC class
rtc_read_time	Get RTC time
rtc_set_time	Set RTC time
rtc_set_ntp_time	Save NTP synchronized time to the RTC
rtc_read_alarm	Get RTC alarm time
rtc_set_alarm	Set RTC alarm time
rtc_irq_set_state	enable/disable 2^N Hz periodic IRQs
rtc_irq_set_freq	set 2^N Hz periodic IRQ frequency for IRQ
rtc_update_irq_enable	enable/disable update IRQ
rtc_alarm_irq_enable	enable/disable alarm IRQ

Examples:

• Read wall time:

  err = rtc_read_time(rtc, &tm);
  

• Set wall time:

  err = rtc_set_time(rtc, &tm);
  

• Set alarm time:

  err = rtc_set_alarm(rtc, &alrm);