6. LED

6.1. Introduction

LED	Pin name	Pin number
Up	GPIO0_C0	16
Down	GPIO0_A4	4

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 C40PL, LEDs are configured as LED class devices.You can control them via /sys/class/leds/.

• Up: User-defined status

• Down: The system is turned on when it is powered on.

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

Upper Lights:

echo 1 > /sys/class/leds/firefly\:yellow\:user/brightness # Upper level lights on
echo 0 > /sys/class/leds/firefly\:yellow\:user/brightness # Upper lights off

Lower level lights:

echo 1 > /sys/class/leds/firefly\:blue\:power/brightness # Lower level lights on
echo 0 > /sys/class/leds/firefly\:blue\:power/brightness # Lower level lights off

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.

Board:sdk/kernel/arch/arm/boot/dts/rv1126-firefly-rk809.dtsi：

leds {
    compatible = "gpio-leds";

	work {
        label = "firefly:blue:power";
        linux,default-trigger = "ir-power-click";
        gpios = <&gpio0 RK_PA4 GPIO_ACTIVE_HIGH>;
        pinctrl-names = "default";
        pinctrl-0 = <&led_power>;
        default-state = "on";
	};
    user {
        label = "firefly:yellow:user";
        linux,default-trigger = "ir-user-click";
        gpios = <&gpio0 RK_PC0 GPIO_ACTIVE_HIGH>;
        pinctrl-names = "default";
        pinctrl-0 = <&led_user>;
        default-state = "on";
	};
};

# pinctrl needs to add GPIO multiplexing control
leds {
	led_power: led-power {
            rockchip,pins = <0 RK_PA4 RK_FUNC_GPIO &pcfg_pull_none>;
        };

        led_user: led-user {
            rockchip,pins = <0 RK_PC0 RK_FUNC_GPIO &pcfg_pull_none>;
        };
};

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 light 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

Save the configuration and compile the kernel, and burn zboot.img to the C40PL board. We can use the serial port to input commands, and we can see the corresponding lights flashing at intervals.

# Upper lights flashing
echo "timer" > /sys/class/leds/firefly\:yellow\:user/trigger

# Lower level lights flashing
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:

$ cat /sys/class/leds/firefly\:yellow\:user/trigger
none rfkill-any rfkill-none mmc0 mmc2 mmc1 [timer] oneshot heartbeat default-on rfkill0 rfkill1 rfkill2 rfkill3