access to GPIO in user space

[JacquesRoubaud]

Hi I have been able to work with GPIO with python on the TEK3 computer, but I always need to work with "sudo" Running a ros node to access gpio in sudo mode is not ideal

back to the basic, I can not simply call "gpioinfo" without starting with sudo. I have been googling a lot, and could not find anything helping. Also, in the linux installation, I could not see a "gpio" group that I could authorize for user swd_sk.

Do you have a suggestion so that user swd_sk can run "gpioinfo" without sudo ?

Many thanks Jacques

[ez-Support]

I would advise you to add sudo access to the script/node you are using: e.g. sudo 777 myScript.py

[ez-Support]

You can also try to add sudo access to the gpio folder: sudo chmod -R a+rwx /sys/class/gpio

[abougouffa]

Another solution is to set the SUID bit of the command you want to run as root.

For example, to set the SUID of gpioinfo, you can run this command:

sudo chmod u+s $(which gpioinfo)

After this, you should be able to call gpioinfo with root permissions and without typing the password.

Note that, for this to work, the owner of the command need to be root. If you need to run a custom user-space command as root without password, you will need to set the SUID bit and set the owner to root like this:

sudo chown root:root /path/to/your/custom/command
sudo chmod u+s /path/to/your/custom/command

[JacquesRoubaud]

None of above worked, and I can't run a "rosrun" with sudo. So I really needed a solution.

I could finally make it using this:

1. Create GPIO group and add swd_sk sudo groupadd gpio sudo usermod -a -G gpio swd_sk newgrp gpio check that gpuoi is part of the output of this command: newgrp gpio here is my output : swd_sk sudo www-data video gpio

2. In /etc/udev/rules.d/10-imx.rules add a last line

   SUBSYSTEM=="gpio", KERNEL=="gpiochip[0-6]", GROUP="gpio", MODE="0660"

reboot

now it's possible to access GPIO in a ROS node

I don't know yet if this is valid for writing to output, but at least this sample program works:

import gpiod
import time

chip=gpiod.Chip('gpiochip0')
line = gpiod.find_line("GPIO_P239")
print("line")
print(line)
lines = chip.get_lines([line.offset()])
print(lines)
lines.request(consumer='foobar', type=gpiod.LINE_REQ_DIR_IN, default_vals=[0])
print('--------')
while True:
      vals = lines.get_values()
      print("=> ", lines.get_values()[0])
      time.sleep(1)
      print()

[GMezWheel]

Hi @JacquesRoubaud, I think your solution is the good one. I also used a udev rule to enable permissions for read/write to usb tty (to avoid sudo).

SUBSYSTEM=="usb", ATTRS{idVendor}=="04d8", MODE="0660"
SUBSYSTEM=="usb_device", ATTRS{idVendor}=="04d8", MODE="0666"

NOTA : permissions 660 allow also write operation