SAMA5D27-SOM1-EK1开发板按键控LED的C代码故障排查求助

Hey there, let's figure out why your LEDs aren't lighting up even though key events are working correctly. I've spotted a few critical issues in your code and setup that are likely causing this:

1. Mismatched Key Code Handling #

Looking at your event output, the key code being detected is 260, but your eval_keycode function only handles BTN_LEFT (code 272) and BTN_RIGHT (code 273). That means when you press the key, the code never enters any of the switch cases—so no LED state changes ever happen!

Fix: #

First, confirm exactly which key code your button is sending. You can either:

• Run cat /proc/bus/input/devices in the terminal to find the input event0 device and its associated key codes, or
• Add a debug print inside the event loop to log every received code:

  if (ev[yalv].type == EV_KEY) {
      printf("%ld.%06ld ", ev[yalv].time.tv_sec, ev[yalv].time.tv_usec);
      printf("type %d code %d value %d\n", ev[yalv].type, ev[yalv].code, ev[yalv].value);
      // Add this debug line
      printf("DEBUG: Key code received: %d\n", ev[yalv].code);
      if (ev[yalv].value == 0)
          eval_keycode(ev[yalv].code);
  }
  

Then update the switch cases in eval_keycode to match your actual key code. For example, if your button uses code 260:

void eval_keycode(int code) {
    static int red_state = 0;
    static int green_state = 0;
    switch (code) {
        case 260: // Use your actual key code here
            printf("Button pressed\n");
            red_state = red_state ? 0 : 1;
            change_led_state(LED_PATH "/" red "/brightness", red_state);
            break;
        // Add a case for a second button if needed
    }
}

2. Key Event Trigger Timing #

Your code currently only calls eval_keycode when ev[yalv].value == 0—that's the release event of the button. If you want the LED to toggle when the button is pressed, change the condition to check for value == 1:

if (ev[yalv].value == 1) // Trigger on key press instead of release
    eval_keycode(ev[yalv].code);

3. Verify LED SysFS Setup #

• Check LED Node Names: Make sure the LED nodes under /sys/class/leds are actually named red and green. Run ls /sys/class/leds in the terminal to see the real node names—they might be something like led0, led1, or user_led instead. If they don't match, update the red and green macros in your code.
• Run as Root: Accessing sysfs LED nodes requires root privileges. Make sure you run your program with sudo (e.g., sudo ./your_program). If you see the error simplekey: unable to access led in the output, this is definitely a permission issue.

4. Manual LED Test #

To rule out hardware or device tree issues, manually control the LEDs from the terminal:

# First disable automatic triggers
echo none > /sys/class/leds/red/trigger
echo none > /sys/class/leds/green/trigger
# Turn red LED on
echo 1 > /sys/class/leds/red/brightness
# Turn it off
echo 0 > /sys/class/leds/red/brightness

If the LED doesn't respond to these commands, the problem is outside your code—check your hardware connections or the device tree configuration for the SAMA5D27 board.

内容的提问来源于stack exchange，提问作者gaston