TIM device tree configuration

1. Article purpose

The purpose of this article is to explain how to configure the timer (TIM) when the peripheral is assigned to Linux^® OS:

• Configuring the timer peripheral to enable PWM, trigger or quadrature encoder.
• Configuring the board, e.g. TIM pins.

The configuration is performed using the device tree mechanism.

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

If the peripheral is assigned to another execution context, refer to How to assign an internal peripheral to a runtime context article for guidelines on peripheral assignment and configuration.

2. DT bindings documentation

The TIM internal peripheral is a multifunction device (MFD).

Each function is represented by a separate DT binding document:

• STM32 TIM MFD device tree bindings document deals with core resources (e.g. registers, clock, DMAs)

• STM32 TIM PWM device tree bindings document deals with PWM resources (e.g. PWM input/output pins)

• STM32 TIM IIO trigger/encoder device tree bindings document deals with other internal peripheral triggering and quadrature encoder resources

3. DT configuration

This hardware description is a combination of both STM32 microprocessor and board device tree files. Refer to Device tree for more explanations about 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)

TIM nodes are declared in stm32mp157c.dtsi.

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

• PWM
• trigger and quadrature encoder

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

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

Warning

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)

This part is used to configure and enable the TIM hardware used on the board:

• Enabling DT root node for the TIM instances in use (e.g timers1...) by setting status = "okay";
• Enabling DT child node(s) for the feature(s) in use (PWM input/output, trigger and quadrature encoder) by setting status = "okay";
• Configuring 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

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"). This is available since ecosystem release ≥ v1.1.0

/* 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)>;
	};
};

Information

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 below is available since ecosystem release ≥ v1.1.0

Information

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)>;
	};
};

Information

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

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";
	};
};

Information

DMA channels 1 and/or 3 for each TIM can be picked from the "dmas" list in stm32mp157c.dtsi file

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 PJ11 as encoder input pins, e.g. TIM1_CH1, TIM1_CH2 (see pinctrl device tree configuration and GPIO internal peripheral)

tim1_in_pins_a: tim1-in-pins-0 {
	pins {
		pinmux = <STM32_PINMUX('E', 9, AF1)>, /* TIM1_CH1 */
			 <STM32_PINMUX('J', 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('J', 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;
	timer@0 {
		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.
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

Please refer to the following links for additional information:

Operating System

Pulse Width Modulation

Device Tree

Multifunction device

Industrial I/O Linux subsystem

Direct Memory Access

Operating System

Pulse Width Modulation

Device Tree

Multifunction device

Industrial I/O Linux subsystem

Direct Memory Access