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2020年11月10日 (二) 10:24的最新版本

Article purpose

本文的目的是解释'在将外围设备分配给 Linux® OS，如何配置“Timer(Tim)”[1] ':

  • 配置定时器peripheral以启用PWM，触发或正交编码器。
  • 配置board，例如 TIM引脚。

使用设备树机制[2]执行配置。

TIM Linux driver 使用它在PWM 和 IIO 框架中注册相关信息。

如果外围设备已分配给另一个执行上下文，请参阅 How to assign an internal peripheral to a runtime context 文章，以获取有关外围设备分配和配置的准则。

DT bindings documentation

“ TIM内部外围设备”[1] 是多功能设备（MFD）。

每个功能由单独的DT绑定文档表示：

  • STM32 TIM MFD设备树绑定[3] 文档涉及核心资源（例如寄存器，时钟，DMA）
  • STM32 TIM PWM设备树绑定[4] 文档涉及PWM资源（例如PWM输入/输出引脚）
  • STM32 TIM IIO触发器/编码器设备树绑定[5]文档涉及其他内部外设触发和正交编码器资源

DT configuration

该硬件描述是STM32微处理器和电路板设备树文件的组合。 有关设备树文件分割的更多说明，请参见Device tree. STM32CubeMX可用于生成板卡设备树。 请参阅[[#How_to_configure_the_DT_using _STM32CubeMX|How to configure the DT using STM32CubeMX]].

DT configuration (STM32 level)

TIM节点在stm32mp157c.dtsi [6].

DT根节点（例如timers1 ...）和DT子节点描述了TIM features ，例如：

  • 触发和正交编码器

它们还描述了硬件参数，例如寄存器地址，时钟和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.png 该设备树部分与STM32微处理器有关。 它必须保持原样，而不能由最终用户修改。

DT configuration (board level)

该部分用于配置和启用板上使用的TIM硬件

  • 通过设置为正在使用的TIM实例（例如timers1 ...）启用'DT根节点'status = "okay";
  • 通过设置 status = "okay"'''为使用中的功能（PWM输入/输出，触发和正交编码器）启用'''DT子节点'''。;
  • 通过pinctrl 到 pinctrl-0, pinctrl-1 和pinctrl-names.

要在板上启用PWM捕获（可选），必须配置DMA：

  • 通过设置dmas = <...>, <...>; 启用与PWM输入对应的DMA通道 匹配 dma-names = "ch1", "ch3";.

不使用PWM捕获时，建议默认情况下禁用DMA通道，以将其备用以用于其他用途：

  • 通过设置/delete-property/dmas 和 /delete-property/dma-names来禁用DMA通道

DT configuration examples

TIM configured in PWM mode

下面的示例显示了如何配置TIM1通道1作为： 

/* 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)>;
	};
};
Info.png PWM输出不需要任何DMA通道。 如果它们在.dtsi文件中默认配置，请禁用它们。 
/* 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";
	};
};

以下的PWM DT用户示例来自ecosystem release ≥ v1.1.0{{#set:Ecosystem release=revision of a previous flow 1.1.0}}

Info.png TIM PWM DT用户说明符编码3个单元：
  • 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"[7] */
	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>;
		};
	};
};

TIM configured in PWM mode and trigger source

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

/* 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)>;
	};
};
Info.png 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";
	};
};

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): 

/* 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";
	};
};
Info.png DMA channels 1 and/or 3 for each TIM can be picked from the "dmas" list in stm32mp157c.dtsi[6] file

TIM configured as quadrature encoder interface

下面的示例显示了如何配置TIM1以与正交编码器接口： 

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 */
	};
};

How to configure the DT using STM32CubeMX

STM32CubeMX 工具可用于配置STM32MPU设备并获取相应的platform configuration device tree 文件
STM32CubeMX可能不支持以上DT bindings documentation 段中描述的所有属性。 如果是这样，该工具会在生成的设备树中插入“用户部分”。 然后可以编辑这些部分以添加一些属性，并将它们一代一代地保留下来。 有关更多信息，请参见STM32CubeMX 用户手册。

References

请参考以下链接以获取更多信息：

  1. ↑ 1.01.1 TIM internal peripheral
  2. ↑ Device tree
  3. ↑ Documentation/devicetree/bindings/mfd/stm32-timers.txt | |}} Documentation/devicetree/bindings/mfd/stm32-timers.txt , STM32 TIM MFD device tree bindings
  4. ↑ Documentation/devicetree/bindings/pwm/pwm-stm32.txt | |}} Documentation/devicetree/bindings/pwm/pwm-stm32.txt , STM32 TIM PWM device tree bindings
  5. ↑ Documentation/devicetree/bindings/iio/timer/stm32-timer-trigger.txt | |}} Documentation/devicetree/bindings/iio/timer/stm32-timer-trigger.txt , STM32 TIM trigger/encoder device tree bindings
  6. ↑ 6.06.1 arch/arm/boot/dts/stm32mp157c.dtsi | |}} stm32mp157c.dtsi , STM32.dtsi file
  7. ↑ 7.07.1 Documentation/devicetree/bindings/leds/leds-pwm.txt| |}} Documentation/devicetree/bindings/leds/leds-pwm.txt , PWM LEDs device tree bindings
取自“http://wiki.100ask.org/index.php?title=TIM_device_tree_configuration&oldid=7765”