6. LED

6.1. Introduction

LEDs can be controlled by using the LED device subsystem or by directly operating GPIO.

6.2. Controlling LEDs by device

Linux has its own LED subsystem for LED devices. In ROC-RK3506B-CC, LEDs are configured as LED class devices.You can control them via /sys/class/leds/.

The default status of the three on-board leds are:

• Blue: Turn on after the system powers on

• Red: defined by user

Users can control each LED by inputting commands to its brightness property through the echo command, for example:

• Blue LED

echo 0 >/sys/class/leds/\:power/brightness  //turn off the blue light
echo 1 >/sys/class/leds/\:power/brightness  //turn on the blue light

• Red LED

echo 0 >/sys/class/leds/\:user/brightness  //turn off the red light
echo 1 >/sys/class/leds/\:user/brightness  //turn on the red light

6.3. Using trigger control LED

Trigger contains a variety of ways to control the LED, here with two examples to illustrate.

• Simple trigger LED

• Complex trigger LED

For more information, please read the document leds-class.txt.

First of all, we need to know how many LED definition, while the corresponding property of the LED is.

Defined LED node in file kernel/arch/arm64/boot/dts/rockchip/rk3506b-firefly-roc-rk3506b-cc.dtsi, like this:

#if LED_GPIO_OR_PWM
	firefly_leds: leds {
		compatible = "pwm-leds";
		status = "okay";
		power_led {
			label = ":power";
			pwms = <&pwm2_8ch_0 0 50000 0>;
			max-brightness = <255>;
			default-state = "on";
			linux,default-trigger = "ir_led";
		};
		user_led {
			label = ":user";
			pwms = <&pwm2_8ch_2 0 50000 0>;
			max-brightness = <255>;
			default-state = "off";
			linux,default-trigger = "none";
		};
	};
#else
	firefly_leds: leds {
		compatible = "gpio-leds";
		status = "okay";
		power_led: power {
			label = ":power";
			linux,default-trigger = "ir-power-click";
			default-state = "on";
			gpios = <&pca9555 PCA_IO1_6 GPIO_ACTIVE_HIGH>;
			pinctrl-names = "default";
		};
		user_led: user {
			label = ":user";
			linux,default-trigger = "ir-user-click";
			default-state = "off";
			gpios = <&pca9555 PCA_IO0_4 GPIO_ACTIVE_HIGH>;
			pinctrl-names = "default";
		};
	};
#endif

Note: The value of compatible must match the one in drivers/leds/leds-gpio.c.

6.3.1. Complex trigger LED

The following is the trigger mode control LED complex example, timer trigger is to let the LED to achieve constant on/off effect.

We need to configure the timer trigger on the kernel.

In the kernel path using make menuconfig, in accordance with the following method to chose timer trigger driver.

Device Drivers
--->LED Support
   --->LED Trigger support
      --->LED Timer Trigger

LED Timer Trigger should be enabled by default. If not, enable it, save defconfig and re-build kernel to take effect.

Echo “timer” to trigger then we can see LED starts to blink.

echo "timer" > /sys/class/leds/\:user/trigger

The user can also use the cat command to get the available values for the trigger:

root@rk3506-buildroot:/# cat /sys/class/leds/\:user/trigger
none rfkill-any rfkill-none kbd-scrolllock kbd-numlock kbd-capslock kbd-kanalock kbd-shiftlock kbd-altgrlock kbd-ctrllock kbd-altlock kbd-shiftllock kbd-shiftrlock kbd-ctrlllock kbd-ctrlrlock mmc0 [timer] rfkill0