LED

Introduction

There are 2 LEDs on the Core-3568J development board, as the following table shows:

PCA_IO1_2 is derived from the GPIO extension chip.

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

Controlling LEDs by device

Linux has its own LED subsystem for LED devices. In Core-3568J, 2 LEDs are configured as LED class devices.

You can control them via /sys/class/leds/.

The default status of the two on-board LEDs are:

• Blue: Turn on after the system powers on.
• Yellow: Defined by the user.

You can change the behavior of each LED by using the echo command to write to its brightness property:

# echo 0 >/sys/class/leds/firefly:blue:power/brightness  //Blue led off
# echo 1 >/sys/class/leds/firefly:blue:power/brightness  //Blue led on

Using trigger control LED

Trigger contains a variety of ways to control the LED; the following two examples illustrate it.

• Simple trigger LED
• Complex trigger LED

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

First of all, you need to know how many LEDs are to be defined and what the corresponding properties of the LEDs are.

Define LED node in file kernel/arch/arm64/boot/dts/rockchip/rk3568-firefly-aioj.dtsi

firefly_leds: leds {
	status = "okay";
	compatible = "gpio-leds";

	power_led: power {
		label = "firefly:blue:power";
		linux,default-trigger = "ir-power-click";
		default-state = "on";
		gpios = <&gpio0 RK_PC0 GPIO_ACTIVE_HIGH>;
		pinctrl-names = "default";
		pinctrl-0 = <&led_power>;
	};

	user_led: user {
		label = "firefly:yellow:user";
		linux,default-trigger = "ir-user-click";
		default-state = "off";
		gpios = <&pca9555 PCA_IO1_2 GPIO_ACTIVE_LOW>;
	};
};

Simple trigger LED

As the name suggests, it is a simple trigger mode to control LEDs. The following configuration turns on the yellow LED by default, and the yellow LED of Core-3568J will be lit after boot.

(1) Define the LED trigger; add the following in kernel/drivers/leds/trigger/led-firefly-demo.c:

DEFINE_LED_TRIGGER(ledtrig_default_control);

(2) Register the trigger.

led_trigger_register_simple("ir-user-click", &ledtrig_default_control);

(3) Control the LED.

led_trigger_event(ledtrig_default_control, LED_FULL);     #yellow led on

(4) Enable LED demo.

led-firefly-demo is disabled by default. If needed, use the following patch to enable the demo driver:

--- a/kernel/arch/arm64/boot/dts/rockchip/rk356x-firefly-demo.dtsi
+++ b/kernel/arch/arm64/boot/dts/rockchip/rk356x-firefly-demo.dtsi
@@ -52,7 +52,7 @@
            led_demo: led_demo {
-                status = "disabled";
+                status = "okay";
                 compatible = "firefly,rk356x-led";
                 };

Complex trigger LED

The following is a more complex example of controlling LEDs with the trigger mode: timer trigger makes the LED blink constantly.

The timer trigger needs to be configured in the kernel.

In the kernel directory, use make menuconfig and select the timer trigger driver as follows:

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

Save the configuration and compile the kernel, then flash kernel.img to the Core-3568J board. Use the serial port to enter the command, and the blue LED will blink at intervals.

echo "timer" > sys/class/leds/firefly\:blue\:power/trigger

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

root@rk3399_firefly_box:/ # cat sys/class/leds/firefly\:blue\:power/trigger
none rc-feedback test_ac-online test_battery-charging-or-full test_battery-charging
test_battery-full test_battery-charging-blink-full-solid test_usb-online mmc0 mmc1
ir-user-click [timer] heartbeat backlight default-on rfkill0 mmc2 rfkill1 rfkill2