AM335x custom device tree using Yocto

Desmond Correia97

I am using Yocto to build a custom image from my Beaglebone black. I need to write a device tree but I can't find any examples of device trees that setup GPIO. I need to configure some pins to be GPIOs.

Could someone provide me with an example. I need to know the comparability properly for GPIO.

I am using linux kernel 4.4 the meta-ti layer

Thanks

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

The software team have been notified. They will respond here.

0 Kemal R. Shakir over 8 years ago in reply to Biser Gatchev-XID

TI__Guru 55345 points

Hello Desmond,

Please, first refer to the kernel documentation.
<Linux kernel>/Documentation/gpio/
<Linux kernel>/Documentation/devicetree/bindings/gpio/gpio-omap.txt

Then you can refer to the am33xx.dtsi, am335x-evm.dts device tree files within the <Processor SDK>/board-support/linux-<version>/arch/arm/boot/dts/

You can refer to these links for general GPIO overview.
processors.wiki.ti.com/.../Processor_SDK_Linux_GPIO
processors.wiki.ti.com/.../Processor_SDK_Linux_GPIO_Driver_Overview
processors.wiki.ti.com/.../Linux_PSP_GPIO_Driver_Guide

This thread also would be in help.
e2e.ti.com/.../547425

Best regards,
Kemal

0 Desmond Correia97 over 8 years ago in reply to Kemal R. Shakir

Prodigy 190 points

Hi Kemal,

I need to control the GPIO from the user space at "/sys/class/gpio/" but I don't see any examples in the "am33xx.dtsi, am335x-evm.dts" that do that? Can you show me an example device three that setups a GPIO so it can be used from ""/sys/class/gpio/".

Thanks

0 Kemal R. Shakir over 8 years ago in reply to Desmond Correia97

TI__Guru 55345 points

Pinmux the pin-outs you have chosen and add their pinctrl-0 to &am33xx_pinmux.
&am33xx_pinmux {
pinctrl-names = "default";
pinctrl-0 = <&gpioX_pins>;
...................................
}

Export the chosen gpio number by echo trough sysfs.
root@am335x-evm:~# echo X > /sys/class/gpio/export

Then control the gpio output by echoing 0 or 1.
root@am335x-evm:~# echo 1 > /sys/class/gpio/gpioX/value

0 Desmond Correia97 over 8 years ago in reply to Kemal R. Shakir

Prodigy 190 points

Hi Kemal,

Thanks you very much for your help. It worked. I do have another problem though.

I need to name the DTB "am335x-boneblack.dtb" or uboot doesn't seem to find it, when I boot the board. I am building with core-image-minimal by the way.

I have created a custom machine configure as well as the recipe file for my custom device tree. I have attached my machine configure for my layer. As you can see KERNEL_DEVICETREE points to my custom device tree. So the build system should pick it up.

#@TYPE: Machine
#@NAME: BeagleBone machine
#@DESCRIPTION: Machine configuration for the http://beagleboard.org/bone board 

require conf/machine/include/ti33x.inc

IMAGE_FSTYPES += "tar.gz"

SERIAL_CONSOLE = "115200 ttyO0"

UBOOT_MACHINE = "am335x_boneblack_config"

PREFERRED_PROVIDER_virtual/kernel = "linux-ti-staging"
PREFERRED_VERSION_linux-ti-staging = "4.4%"

# Increase this everytime you change something in the kernel
#MACHINE_KERNEL_PR ?= "r22"

KERNEL_DEVICETREE = "am335x-boneblack-reeds.dtb"
KERNEL_DEVICETREE_bbbreeds = "am335x-boneblack-reeds.dtb"

0 Desmond Correia97 over 8 years ago in reply to Desmond Correia97

Prodigy 190 points

Hi,

Just wanted to let you know that I have resoled the problem with the device tree. A user can create a uEnv.txt file so that uboot knows which device tree to use or you can create a symbolic link to your DTB using the name am335x-boneblack.dtb

Both work

Processors

Processors forum

AM335x custom device tree using Yocto