RTC device tree configuration

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1. Article purpose[edit source]

The purpose of this article is to explain how to configure the RTC internal peripheral when it is assigned to the Linux^® OS. In that case, it is controlled by the RTC framework.

The configuration is performed using the device tree mechanism that provides a hardware description of the RTC peripheral, used by the STM32 RTC Linux driver.

2. DT bindings documentation[edit source]

The RTC internal peripheral is represented by the STM32 RTC device tree bindings^[1]

3. DT configuration[edit source]

This hardware description is a combination of STM32 microprocessor and board device tree files. See Device tree for explanations on device tree file split.

The STM32CubeMX can be used to generate the board device tree. Refer to How to configure the DT using STM32CubeMX for more details.

3.1. DT configuration (STM32 level)[edit source]

The RTC node is declared in stm32mp157c.dtsi^[2]. It describes the hardware register address, clocks and interrupts.

rtc: rtc@5c004000 {
	compatible = "st,stm32mp1-rtc";
	reg = <0x5c004000 0x400>;                               --> Register location and length
	clocks = <&rcc RTCAPB>, <&rcc RTC>;
	clock-names = "pclk", "rtc_ck";
	interrupts = <GIC_SPI 3 IRQ_TYPE_LEVEL_HIGH>;
	status = "disabled";
};

Warning

This device tree part is related to STM32 microprocessors. It should be kept as is, without being modified by the end-user.

3.2. DT configuration (board level)[edit source]

The objective of this chapter is to explain how to configure the DT nodes related to the STM32 board.
Thanks to this chapter, the end-user must be able to configure any parameters via the DT to adapt to a new board.
The below warning can be added.

3.3. DT configuration examples[edit source]

This chapter must provide an example of how to configure the DT to adapt it to a new board.

4. How to configure the DT using STM32CubeMX[edit source]

The STM32CubeMX tool can be used to configure the STM32MPU device and get the corresponding platform configuration device tree files.
The STM32CubeMX may not support all the properties described in the above DT bindings documentation paragraph. If so, the tool inserts user sections in the generated device tree. These sections can then be edited to add some properties and they are preserved from one generation to another. Refer to STM32CubeMX user manual for further information.

5. References[edit source]

Please refer to the following links for additional information:

[1] Device tree bindings

[2] STM32MP157C device tree

[1]

[2]