TIM device tree configuration

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

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1. Article purpose

The purpose of this article is to explain how to configure the TIM internal peripheral using the device tree mechanism, relying on the bindings documentation, that is the description of the required and optional device-tree properties.

When the peripheral is assigned to Linux^® OS, it explains:

• how to enable PWM, trigger or quadrature encoder.
• how to configure the board, e.g. TIM input/output pins.

It is used by the TIM Linux driver that registers relevant information in PWM, IIO and counter frameworks.

The peripheral can be assigned to different contexts/software components, depending on the final product needs. Refer to How to assign an internal peripheral to an execution context for guidelines on this configuration.

2. DT bindings documentation

The device tree binding documents are stored in the Linux kernel repository:

• Linux^® OS : Documentation/devicetree/bindings/mfd/mfd/st,stm32-timers.yaml

The TIM internal peripheral is a multifunction device (MFD), providing several functions represented by a separate compatible string:

• st,stm32-timers deals with core resources. (e.g. registers, clock, DMAs)
• st,stm32-pwm deals with PWM resources. (e.g. PWM input/output pins)
• st,stm32-timer-trigger deals with trigger resources (e.g. trigger output connected to other STM32 internal peripherals)
• st,stm32-timer-counter deals with quadrature encoder resources and external events counter.

3. DT configuration

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 organization.

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)

DT root node (e.g. timers1...) and DT child nodes describe the TIM features such as:

• PWM
• trigger
• counter and quadrature encoder

They also describe hardware parameters such as registers address, clock and DMA.

3.1.1. On STM32MP1 series

TIM nodes are declared in stm32mp131.dtsi on STM32MP13x lines .

TIM nodes are declared in stm32mp151.dtsi on STM32MP15x lines .

timers1: timer@address {
	/* timer common resources */
	compatible = "st,stm32-timers";
	...
	pwm {
		/* PWM*/
		compatible = "st,stm32-pwm";
	};
	timer@0 {
		compatible = "st,stm32h7-timer-trigger";
		/* trigger identifier (e.g. 0 for TIM1 triggers, 1 for TIM2... */
		reg = <0>;
	};
	counter {
		compatible = "st,stm32-timer-counter";
	};
};

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

3.1.2. On STM32MP2 series

TIM nodes are declared in stm32mp251.dtsi on STM32MP25x lines .

timers1: timer@address {
	/* timer common resources */
	compatible = "st,stm32mp25-timers";
	...
	pwm {
		/* PWM*/
		compatible = "st,stm32mp25-pwm";
	};
	timer@0 {
		compatible = "st,stm32mp25-timer-trigger";
		/* trigger identifier (e.g. 0 for TIM1 triggers, 1 for TIM2... */
		reg = <0>;
	};
	counter {
		compatible = "st,stm32mp25-timer-counter";
	};
};

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

3.2. DT configuration (board level)

The objective of this chapter is to explain how to enable and configure the TIM DT nodes for a board:

• Enable DT root node for the TIM instances in use (e.g timers1...) by setting status = "okay";
• Enable DT child node(s) for the feature(s) in use (PWM input/output, trigger and quadrature encoder) by setting status = "okay";
• Configure pins in use via pinctrl through pinctrl-0, pinctrl-1 and pinctrl-names.

To enable PWM capture on the board (optional), DMA must be configured:

• Enable DMA channel(s) corresponding to the PWM input(s) by setting dmas = <...>, <...>; and matching dma-names = "ch1", "ch3";.

When PWM capture isn't used, it's recommended to disable DMA channels by default, to spare them for other usage:

• Disable DMA channels by setting /delete-property/dmas and /delete-property/dma-names

Peripheral configuration should be done in specific board device tree files (board dts file and pinctrl dtsi file).

3.3. DT configuration examples

3.3.1. TIM configured in PWM mode

The example below shows how to configure TIM1 channel 1 to act as:

• PWM output on PE9, e.g. TIM1_CH1 (See pinctrl device tree configuration and GPIO internal peripheral)
• PWM device tree provider (e.g. TIM1_CH1) used by a device tree consumer (e.g. like "pwm-leds").

/* select TIM1_CH1 alternate function 1 on 'PE9' */
pwm1_pins_a: pwm1-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, AF1)>;
		bias-pull-down;
		drive-push-pull;
		slew-rate = <0>;
	};
};

/* configure 'PE9' as analog input in low-power mode */
pwm1_sleep_pins_a: pwm1-sleep-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, ANALOG)>;
	};
};

The PWM output doesn't require any DMA channel. Disable them if they are configured by default in the .dtsi file.

/* PWM DT provider on TIM1: "pwm1" */
&timers1 {
	status = "okay";
	/* spare all DMA channels since they are not needed for PWM output */
	/delete-property/dmas;
	/delete-property/dma-names;
	/* define pwm1 label */
	pwm1: pwm {
		/* configure PWM pins on TIM1_CH1 */
		pinctrl-0 = <&pwm1_pins_a>;
		pinctrl-1 = <&pwm1_sleep_pins_a>;
		pinctrl-names = "default", "sleep";
		/* enable PWM on TIM1 */
		status = "okay";
	};
};

• PWM DT user example

The TIM PWM DT user specifier encodes 3 cells: PWM number (0 for CH1, 1 for CH2 and so on) PWM period in nanoseconds PWM polarity (0 for normal polarity or PWM_POLARITY_INVERTED)

/ {
	...
	/* PWM DT user on TIM1_CH1: "pwm1", example with "pwm-leds" */
	pwmleds {
		compatible = "pwm-leds";
		example {
			label = "stm32-pwm-leds-example";
			/* Use pwm1 channel 0 (e.g. TIM1_CH1) */
			/* period in nanoseconds (500000), normal polarity (0) */
			pwms = <&pwm1 0 500000 0>;
			max-brightness = <127>;
		};
	};
};

3.3.2. TIM configured in PWM mode and trigger source

The example below shows how to configure TIM1 channel 1 to act as:

• PWM output on PE9, e.g. TIM1_CH1 (See pinctrl device tree configuration and GPIO internal peripheral)
• trigger source (synchronous with PWM) for other internal peripheral such as STM32 ADC

/* select TIM1_CH1 alternate function 1 on 'PE9' */
pwm1_pins_a: pwm1-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, AF1)>;
		bias-pull-down;
		drive-push-pull;
		slew-rate = <0>;
	};
};

/* configure 'PE9' as analog input in low-power mode */
pwm1_sleep_pins_a: pwm1-sleep-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, ANALOG)>;
	};
};

The PWM output doesn't require any DMA channel. Disable them if they are configured by default in the .dtsi file.

&timers1 {
	status = "okay";
	/* spare all DMA channels since they are not needed for PWM output */
	/delete-property/dmas;
	/delete-property/dma-names;
	pwm {
		/* configure PWM on TIM1_CH1 */
		pinctrl-0 = <&pwm1_pins_a>;          
		pinctrl-1 = <&pwm1_sleep_pins_a>;
		pinctrl-names = "default", "sleep";
		/* enable PWM on TIM1 */
		status = "okay";
	};
	timer@0 {
		/* enable trigger on TIM1 */
		status = "okay";
	};
};

3.3.3. TIM configured in PWM input capture mode

This chapter is only applicable for STM32MP1 series.

The example below shows how to configure TIM1 channel 1 in PWM input capture mode (e.g. period and duty cycle):

• Configure PWM input on PE9, e.g. TIM1_CH1 (See pinctrl device tree configuration and GPIO internal peripheral)

/* select TIM1_CH1 alternate function 1 on 'PE9' */
pwm1_in_pins_a: pwm1-in-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, AF1)>;
		bias-disable;
	};
};

/* configure 'PE9' as analog input in low-power mode */
pwm1_in_sleep_pins_a: pwm1-in-sleep-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, ANALOG)>;
	};
};

A DMA channel is required and must be configured depending on the PWM input channel:

• Select DMA channel 1, "ch1", to capture PWM input channel 1 and/or 2
• Select DMA channel 3, "ch3", to capture PWM input channel 3 and/or 4
• Select both "ch1" and "ch3" dmas to enable capture on all PWM input channels

&timers1 {
	status = "okay";
	/* Enable DMA "ch1" for PWM input on TIM1_CH1 */
	dmas = <&dmamux1 11 0x400 0x5>;
	dma-names = "ch1";
	pwm {
		/* configure PWM input pins, e.g. TIM1_CH1 */
		pinctrl-0 = <&pwm1_in_pins_a>;
		pinctrl-1 = <&pwm1_in_sleep_pins_a>;
		pinctrl-names = "default", "sleep";
		/* enable PWM on TIM1 */
		status = "okay";
	};
};

DMA channels 1 and/or 3 for each TIM can be picked from the "dmas" list in stm32mp131.dtsi or stm32mp151.dtsi files

3.3.4. TIM configured as quadrature encoder interface

The example below shows how to configure TIM1 to interface with a quadrature encoder:

• Configure PE9 and PE11 as encoder input pins, e.g. TIM1_CH1, TIM1_CH2 (see pinctrl device tree configuration and GPIO internal peripheral)

On the STM32MP157X-DKX discovery board, TIM1_CH1 and TIM1_CH2 signals are accessible via the D6 and D10 pins of the Arduino Uno connector.

tim1_in_pins_a: tim1-in-pins-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, AF1)>, /* TIM1_CH1 */
			 <STM32_PINMUX('E', 11, AF1)>; /* TIM1_CH2 */
		bias-disable;
	};
};

tim1_in_pins_sleep_a: tim1-in-pins-sleep-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, ANALOG)>, /* TIM1_CH1 */
			 <STM32_PINMUX('E', 11, ANALOG)>; /* TIM1_CH2 */
	};
};

&timers1 {
	status = "okay";
	/delete-property/dmas;                       /* spare all DMA channels since they are not required for quadrature encoder interface */
	/delete-property/dma-names;
	counter {
		pinctrl-0 = <&tim1_in_pins_a>;       /* configure TIM1_CH1 and TIM1_CH2 as encoder input pins */
		pinctrl-1 = <&tim1_in_pins_sleep_a>;
		pinctrl-names = "default", "sleep";
		status = "okay";                     /* enable Encoder interface mode on TIM1 */
	};
};

4. How to configure the DT using STM32CubeMX

The STM32CubeMX tool can be used to configure the STM32MPU device and get the corresponding platform configuration device tree files.
STM32CubeMX may not support all the properties described in DT binding files listed 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

Refer to the following links for additional information: