基于Raspberry Pi 4 GPIO事件触发Xorg空闲时间重置/停止feh屏保的方案咨询（含NodeRed实现路径）

Perfect scenario to solve without reinventing the wheel! Let’s walk through three solid, interrupt-driven solutions that play nice with your existing Node-RED setup and avoid GPIO conflicts:

1. Use Node-RED Directly (Simplest, No Extra Tools) #

Since Node-RED already has exclusive access to your GPIO button, leverage that to control the screensaver directly—no need to fight over pins:

• Kill feh when the button is pressed
  Add an exec node to your Node-RED flow, triggered by the GPIO button input. Configure it to run this command:

  pkill feh
  

  If you’re running feh with specific arguments (like slideshow mode), make it more precise to avoid killing unrelated processes:

  pkill -f "feh --slideshow /path/to/images"
  

• Reset Xorg idle time (instead of killing feh)
  If you prefer to keep feh running but reset the idle timer so your xprintidle script doesn’t trigger it, install xdotool first:

  sudo apt install xdotool
  

  Then use this command in the Node-RED exec node to simulate a tiny, invisible mouse movement (resets the idle counter):

  xdotool mousemove 1 1 && xdotool mousemove 0 0
  

  This works because Xorg registers mouse movement as user activity, resetting the idle timer tracked by xprintidle.

2. System-Level GPIO Interrupts with libgpiod (Avoid Library Conflicts) #

If you want a standalone solution that doesn’t rely on Node-RED, use libgpiod—the official kernel-level GPIO library for Raspberry Pi, which supports multiple processes accessing GPIO pins safely (no conflict with Node-RED’s GPIO usage):

1. Install the required packages:

   sudo apt install gpiod python3-gpiod
   

2. Create a Python script (e.g., screensaver_stop.py) with this interrupt-driven code (replace the GPIO pin number with yours):

   import gpiod
   import subprocess
   
   # Configure your GPIO pin (adjust line number to match your button)
   CHIP_NAME = "gpiochip0"
   BUTTON_PIN = 17
   
   # Set up GPIO line for edge detection (adjust edge type for your hardware)
   chip = gpiod.Chip(CHIP_NAME)
   button_line = chip.get_line(BUTTON_PIN)
   request_config = gpiod.line_request()
   request_config.request_type = gpiod.line_request.EVENT_FALLING_EDGE
   request_config.consumer = "screensaver_handler"
   
   try:
       button_line.request(request_config)
       print("Waiting for button press...")
       while True:
           # Wait for a GPIO event (interrupt-driven, no polling!)
           if button_line.event_wait(sec=1):
               event = button_line.read_event()
               # Trigger screensaver stop
               subprocess.run(["pkill", "feh"], check=False)
               # Optional: Reset idle time instead
               # subprocess.run(["xdotool", "mousemove", "1", "1", "&&", "xdotool", "mousemove", "0", "0"], shell=True, check=False)
   finally:
       button_line.release()
       chip.close()
   

3. Run the script on startup (add it to rc.local or create a systemd service) so it runs in the background.

3. Inter-Process Communication (IPC) Between Python Script and Node-RED #

If you want to keep your existing xprintidle/Python screensaver logic intact, set up IPC to let Node-RED notify the script when the button is pressed:

• Local MQTT Broker: Install Mosquitto on your Pi (sudo apt install mosquitto mosquitto-clients). In Node-RED, add an MQTT Out node that sends a message (e.g., stop_screensaver) to a local topic (like home/screensaver/control) when the button is pressed. Modify your Python script to subscribe to this topic and trigger the screensaver stop when the message is received.
• Unix Socket: Add a simple Unix socket server to your Python script. In Node-RED, use an exec node to send a short message to the socket (e.g., echo "stop" | nc -U /tmp/screensaver.sock), which triggers the script to kill feh or reset the idle timer.

内容的提问来源于stack exchange，提问作者Valentino