Can't use the character '_' in the .overlay file.

Question

I tried to write the following simple '.overlay' file:

// To get started, press Ctrl+Space to bring up the completion menu and view the available nodes.

// You can also use the buttons in the sidebar to perform actions on nodes.
// Actions currently available include:

// * Enabling / disabling the node
// * Adding the bus to a bus
// * Removing the node
// * Connecting ADC channels

// For more help, browse the DeviceTree documentation at https://docs.zephyrproject.org/latest/guides/dts/index.html
// You can also visit the nRF DeviceTree extension documentation at https://docs.nordicsemi.com/bundle/nrf-connect-vscode/page/guides/ncs_configure_app.html#devicetree-support-in-the-extension
&gpio0 {
	status = "okay";
};

&gpiote {
	status = "okay";
};


/ {
	leds {
		compatible = "gpio-leds";
		yellow_led: led21 {
			label = "led";
			gpios = <&gpio0 6 GPIO_ACTIVE_HIGH>;
		};
	};

	aliases {
		yellow_led = &yellow_led;
	};
};

However, I am getting the following error:

devicetree error: /aliases: alias property name 'yellow_led' should include only characters from [0-9a-z-]
CMake Error at /home/ams/ncs/v2.9.0/zephyr/cmake/modules/dts.cmake:295 (execute_process):

but if you look inside the .dts files provided by the 'nrf52dk' I can see the following node:

	pwmleds {
		compatible = "pwm-leds";
		pwm_led0: pwm_led_0 {
			pwms = <&pwm0 0 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
		};
	};

so why it's allowed in the .dts file of the board but not in the .overlay file?

Priyanka · Accepted Answer

Hi, 
 It's not whether you use in .dts or .overlay, rather, it is only an issue when using underscore in the aliases. 
 You can use underscore when naming the node names or label names but avoid them when using aliases. 
 -Priyanka

Can't use the character '_' in the .overlay file.

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