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

带有所有必需或可选属性的“ STM32 DAC设备树绑定” 协议。

DT configuration

该硬件描述是STM32和电路板设备树文件的组合。 有关分割设备树文件的说明，请参见 Device tree。

STM32CubeMX可用于生成板卡设备树。 有关更多详细信息，请参考How to configure the DT using STM32CubeMX 。

DT configuration (STM32 level)

DAC节点在stm32mp157c.dtsi中声明:

• DT根节点（'dac'）描述DAC硬件模块参数，例如寄存器区域和时钟。
• DT子节点（'dac1'和'dac2'）独立描述DAC通道。

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. */
	};
};

该设备树部分与STM32微处理器有关。 它应该保持原样，而不要由最终用户修改。

DT configuration (board level)

请按照以下顺序在板上配置和启用DAC：

• 通过设置status =“ okay”启用名为'dac'的DT根节点。
• 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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