Last edited 8 months ago

RTC device tree configuration

Applicable for STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

1. Article purpose[edit source]

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 source]

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

3. DT configuration[edit source]

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 source]

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]
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";
};

The STM32MP2 RTC node is located

  • for STM32MP25x lines More info.png in stm32mp251.dtsi [4]
rtc: rtc@46000000 {
	compatible = "st,stm32mp25-rtc";
	reg = <0x46000000 0x400>;                               --> Register location and length
	clocks = <&scmi_clk CK_SCMI_RTC>,
                 <&scmi_clk CK_SCMI_RTCCK>;
	clock-names = "pclk", "rtc_ck";
	interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
	status = "disabled";
};

It describes the hardware register address, clocks and interrupts.

See Device tree for further explanation.

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 source]

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 [5]. A pinctrl state named "default" can be defined to reserve a pin for the RTC output.

3.3. DT configuration examples[edit source]

#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 STM32MPx boards [6] 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 source]

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 source]

Please refer to the following links for additional information: