Troubles when adding a LED to Device Tree

[phfbertoleti]

Hi. First of all, thanks in advance for those who try to help me.

I'm studying about Device Trees, and I've chosen to use Beaglebone Green Wireless as a board to practice.

I've done the following steps:

1) From u-boot serial, I've seen that Beaglebone green Wireless is using uses am335x-bonegreen-wireless-uboot-univ.dtb as DTB file

2) Cloned / downloaded beaglebone Kernel (from https://github.com/beagleboard/linux)

3) I want to add LED at GPIO 47 ( = GPIO1_16, and accordingly to board schematic, AM33xx GPMC_A0 pin). I've edited am335x-bone-common.dtsi file, adding led (led6) in leds node as follows:

leds {
	pinctrl-names = "default";
	pinctrl-0 = <&user_leds_s0>;
	compatible = "gpio-leds";
	led2 {
	label = "beaglebone:green:usr0";
	gpios = <&gpio1 21 GPIO_ACTIVE_HIGH>;
	linux,default-trigger = "heartbeat";
	default-state = "off";
	};
	led3 {
	label = "beaglebone:green:usr1";
	gpios = <&gpio1 22 GPIO_ACTIVE_HIGH>;
	linux,default-trigger = "mmc0";
	default-state = "off";
	};
	led4 {
	label = "beaglebone:green:usr2";
	gpios = <&gpio1 23 GPIO_ACTIVE_HIGH>;
	linux,default-trigger = "cpu0";
	default-state = "off";
	};
	led5 {
	label = "beaglebone:green:usr3";
	gpios = <&gpio1 24 GPIO_ACTIVE_HIGH>;
	linux,default-trigger = "mmc1";
	default-state = "off";
	};                 led6 { label = "beaglebone:green:extLed"; gpios = <&gpio1 16 GPIO_ACTIVE_HIGH>; linux,default-trigger = "heartbeat"; default-state = "off"; };
	};

And I've added gpio2_16 in pinmux of user leds, as follows:

&am33xx_pinmux {
	user_leds_s0: user_leds_s0 {
	pinctrl-single,pins = <
	AM33XX_PADCONF(AM335X_PIN_GPMC_A5, PIN_OUTPUT_PULLDOWN, MUX_MODE7)      /* gpmc_a5.gpio1_21 */
	AM33XX_PADCONF(AM335X_PIN_GPMC_A6, PIN_OUTPUT_PULLUP, MUX_MODE7)        /* gpmc_a6.gpio1_22 */
	AM33XX_PADCONF(AM335X_PIN_GPMC_A7, PIN_OUTPUT_PULLDOWN, MUX_MODE7)      /* gpmc_a7.gpio1_23 */
	AM33XX_PADCONF(AM335X_PIN_GPMC_A8, PIN_OUTPUT_PULLUP, MUX_MODE7)        /* gpmc_a8.gpio1_24 */                   AM33XX_PADCONF(AM335X_PIN_GPMC_A0, PIN_OUTPUT_PULLUP, MUX_MODE7)        /* gpmc_a0.gpio1_16 */
	>;
	};

4) I've successfully compiled all dtbs by doing:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- dtbs

5) After that, I've updated the recently compiled am335x-bonegreen-wireless-uboot-univ.dtb file to /boot/dtbs/{uname-r} folder in Beaglebone Green

6) And, finally, I rebooted the board. However, board has entered in a "strange state", with all user leds powered on. Using U-Boot serial, I've noticed that boot process have stopped at "starting kernel" message

In this case, what have I done wrong? Are my modifications in DTS file right? 

Again, thanks in advance.

[TJF]

Hi!

Forget about all that device tree trouble, use libpruio instead. You can configure the pin and set the desired output state by a single function call in your programm running at user space (no sudo commands, no rebooting, ...)

gpio_setValue(Io, P9_15, 1) // configure and set high

gpio_setValue(Io, P9_15, 0) // set low

 

You'll have faster boot, less memory consumption, and your code executes much faster (compared with sysfs GPIO control).

You may want to check out some examples.

Regards

[Mark A. Yoder]

Your steps look right, but there is a simpler way to do them.  Check out:

https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED

No need to cross compile etc.

--Mark

[phfbertoleti]

Hi TJF. 

I've never heard about libpruio before. It seems to be very nice and fast, once it uses PRUs for writing and reading I/Os, per my understanding. Thanks for the suggestion.

Best Regards, 
Pedro Bertoleti

[phfbertoleti]

Hi Mark. Great, thanks!

Per my understanding, the Device Tree approach of https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED doesn't include modifying user_leds_s0 (pinmux for user leds). Do you know why isn't this needed?

Best Regards,

Pedro Bertoleti

[Mark A. Yoder]

Pedro:

  I think I got lucky and the mux was already set to gpio.

--Mark