RTC device tree configuration

Applicable for STM32MP13x lines, STM32MP15x lines

1 Article purpose[edit]

This article explains how to configure the RTC internal peripheral when it is assigned to the Linux® OS. In this 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]

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

3 DT configuration[edit]

This hardware description is a combination of the STM32 microprocessor device tree files (.dtsi extension) and board device tree files (.dts extension). See the Device tree for an explanation of the device tree file split.

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]

The STM32MP1 RTC node is located

  • for STM32MP13x lines More info.png in stm32mp131.dtsi [2]
  • for STM32MP15x lines More info.png in stm32mp151.dtsi [3]

It describes the hardware register address, clocks and interrupts.

See Device tree for further explanation.

rtc: rtc@5c004000 {
	compatible = "st,stm32mp1-rtc";
	reg = <0x5c004000 0x400>;                               --> Register location and length
	clocks = <&scmi0_clk CK_SCMI0_RTCAPB>,
                 <&scmi0_clk CK_SCMI0_RTC>;
	clock-names = "pclk", "rtc_ck";
	interrupts-extended = <&exti 19 IRQ_TYPE_LEVEL_HIGH>;
	status = "disabled";
Warning white.png 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]

This part is used to enable the RTC used on a board, which is done by setting the status property to okay.

RTC pin output properties :

  • "st,lsco" property is available to select and enable the RTC output on which RTC low-speed clock is output.
  • "st,alarm" property is available to select and enable the RTC output on which RTC Alarm A is output.

The values of theses properties are defined in [4]. A pinctrl state named "default" can be defined to reserve a pin for the RTC output.

3.3 DT configuration examples[edit]

#include <dt-bindings/rtc/rtc-stm32.h>
&rtc {
	st,alarm = <RTC_OUT1>;
	st,lsco = <RTC_OUT2_RMP>;
	pinctrl-0 = <&rtc_out1_pins_a &rtc_out2_rmp_pins_a>;
	pinctrl-names = "default";
	status = "okay"; 

As example, on STM32MP1 boards [5] st,alarm could be used to trigger STPMIC1 WAKEUP pin. In this case, pinctrl rtc_out1_pins_a should be configured like that :

rtc_out1_pins_a: rtc-out1-pins-0 {
	pins {
		pinmux = <STM32_PINMUX('C', 13, ANALOG)>; /* RTC_OUT1 */

4 How to configure the DT using STM32CubeMX[edit]

The STM32CubeMX tool can be used to configure the STM32MPU device and get the corresponding platform configuration device tree files.
STM32CubeMX might 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]

Please refer to the following links for additional information: