DAC device tree configuration

Purpose

本文旨在说明将数模转换器(DAC) 分配给 Linux^® 操作系统时如何进行配置, 尤其是:

• 如何配置和启用DACperipheral
• 如何配置板、DAC通道、基准电压调节器和引脚。

使用设备树机制执行配置.

DAC Linux driver使用它在 IIO framework中注册相关信息，例如IIO设备，通道和电压标度。

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

STM32 DAC device tree bindings deal with all the required or optional properties.

DT configuration

This hardware description is a combination of STM32 and board device tree files. See Device tree for explanations on 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.

DT configuration (STM32 level)

The DAC nodes are declared in stm32mp157c.dtsi:

• DT root node ('dac') describes the DAC hardware block parameters such as registers area and clocks.
• DT child nodes ('dac1' and 'dac2') describe DAC channels independently.

dac: dac@address {
	compatible = "st,stm32h7-dac-core";
	...                                                                            /* common resources in 'dac' root node. */
	dac1: dac@1 {
		compatible = "st,stm32-dac";
		reg = <1>;                                                             /* DAC identifier (e.g. 1 for DAC1) */
		...                                                                    /* private resources in 'dac1' child node. */
	};
	dac2: dac@2 {
		compatible = "st,stm32-dac";
		reg = <2>;                                                             /* DAC identifier (e.g. 2 for DAC2) */
		...                                                                    /* private resources in 'dac2' child node. */
	};
};

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

DT configuration (board level)

Follow the below sequence to configure and enable the DAC on your board:

• Enable DT root node named 'dac' by setting status = "okay".
• Configure pins in use via pinctrl through pinctrl-0 and pinctrl-names.
• Configure analog reference voltage regulator by setting vref-supply = <&your_regulator>.
• Enable DT child node(s) for 'dac1' and/or 'dac2' channels(s) in use by setting status = "okay".

The DAC can use the internal VREFBUF or any other external regulator wired to the VREF+ pin

.

DT configuration example

The example below shows how to configure DAC1 and DAC2 channels:

• PA4 and PA5 pins both configured as analog pins (see Pinctrl device tree configuration for more details)
• VREFBUF used as reference voltage

dac_ch1_pins_a: dac-ch1 {
	pins {
		pinmux = <STM32_PINMUX('A', 4, ANALOG)>;                 /* configure 'PA4' as ANALOG */
	};
};
dac_ch2_pins_a: dac-ch2 {
	pins {
		pinmux = <STM32_PINMUX('A', 5, ANALOG)>;                 /* configure 'PA5' as ANALOG */
	};
};

&dac {
	pinctrl-names = "default";
	pinctrl-0 = <&dac_ch1_pins_a &dac_ch2_pins_a>;                   /* Use PA4 and PA5 pin as ANALOG */
	vref-supply = <&vrefbuf>;                                        /* Example to use VREFBUF (It needs to be enabled as well) */
	status = "okay";                                                 /* Enable the DAC block */
	dac1: dac@1 {
		status = "okay";                                         /* Enable DAC1 */
	};
	dac2: dac@2 {
		status = "okay";                                         /* Enable DAC2 */
	};
};

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.

References

For additional information, refer to the following links:

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