RTC overview

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP21x lines, STM32MP23x lines, STM32MP25x lines

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This article gives information about the Linux^® RTC framework. The RTC framework is involved in precise time countdown.

1. Framework purpose

The RTC keeps the system time up-to-date and can wake up the system from the standby power mode at a programmed time.

A general presentation of the RTC framework is available in the Linux RTC documentation .

2. System overview

2.1. Component description

• RTC (hardware)

RTC dedicated hardware block in STM32MPU product.

• rtc-stm32

RTC ST driver.

• rtc

Linux RTC framework, it provides API to RTC driver and interfaces to user.

• Sysfs interface

Sysfs interface is accessible via /sys/class/rtc/rtcX/.

• Procfs interface

Procfs interface is accessible via /proc/driver/rtc.

• Char device interface

Device interface is accessible via /dev/rtcX.

• User application

The user application can be a user built application or an community application such as hwclock.

2.2. API description

API is described in Linux RTC documentation .

3. Configuration

3.1. Kernel configuration

Activate rtc-stm32 driver in kernel configuration using the Linux Menuconfig tool: Menuconfig or how to configure kernel

Device drivers  --->
    -*- Real Time Clock  --->
        <*> STM32 RTC

3.2. Device tree configuration

Refer to the RTC device tree configuration.

4. How to use the framework

Refer to the How to use the RTC.

5. How to trace and debug the framework

5.1. How to trace

Dynamic debug traces can be added using the following command:

echo -n 'file rtc-stm32.c +p'>/sys/kernel/debug/dynamic_debug/control

6. Source code location

• rtc-stm32: drivers/rtc/rtc-stm32.c
• api: include/linux/rtc.h
• framework:
  • drivers/rtc/class.c
  • drivers/rtc/dev.c
  • drivers/rtc/interface.c
  • drivers/rtc/lib.c
  • drivers/rtc/proc.c
  • drivers/rtc/sysfs.c
• device-tree bindings constants: include/dt-bindings/rtc/rtc-stm32.h