reterminal-dm4/archive/chromium-setup-legacy/LED-SUMMARY.md

reTerminal DM4 LED Summary

Total LEDs Available: 9

User-Controllable LEDs: 2

1. usr-led - User-controllable LED

   • Path: /sys/class/leds/usr-led/brightness
   • Max brightness: 1 (on/off)
   • Status: ✅ Controllable (may not be physically visible on all models)
   • Control: echo 1 | sudo tee /sys/class/leds/usr-led/brightness (ON)
   • Control: echo 0 | sudo tee /sys/class/leds/usr-led/brightness (OFF)

2. usr-buzzer - User-controllable buzzer (controlled like LED)

   • Path: /sys/class/leds/usr-buzzer/brightness
   • Max brightness: 1 (on/off)
   • Status: ✅ Controllable and confirmed working
   • Control: echo 1 | sudo tee /sys/class/leds/usr-buzzer/brightness (ON)
   • Control: echo 0 | sudo tee /sys/class/leds/usr-buzzer/brightness (OFF)
   • Note: This is actually a buzzer, not an LED, but uses the same control interface

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System-Controlled LEDs: 7

These LEDs are managed by the system and typically not user-controllable:

1. ACT - Activity LED (SD card activity)

   • Path: /sys/class/leds/ACT/brightness
   • Max brightness: 1
   • Trigger: mmc0 (blinks on SD card activity)
   • Status: System-controlled (read-only for users)

2. audio-pwr - Audio power LED

   • Path: /sys/class/leds/audio-pwr/brightness
   • Max brightness: 1
   • Trigger: none
   • Status: System-controlled (indicates audio power state)

3. default-on - Virtual LED (always on)

   • Path: /sys/class/leds/default-on/brightness
   • Max brightness: 255
   • Trigger: default-on
   • Status: System-controlled virtual LED

4. lcd-pwr - LCD power LED

   • Path: /sys/class/leds/lcd-pwr/brightness
   • Max brightness: 1
   • Trigger: none
   • Status: System-controlled (indicates LCD power state)

5. mmc0 - SD card activity LED (primary)

   • Path: /sys/class/leds/mmc0/brightness
   • Max brightness: 255
   • Trigger: mmc0 (blinks on SD card activity)
   • Status: System-controlled

6. mmc0:: - SD card activity LED (secondary)

   • Path: /sys/class/leds/mmc0::/brightness
   • Max brightness: 255
   • Trigger: mmc0 (blinks on SD card activity)
   • Status: System-controlled

7. PWR - Power LED

   • Path: /sys/class/leds/PWR/brightness
   • Max brightness: 1
   • Trigger: default-on (always on when powered)
   • Status: System-controlled (indicates power state)

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Summary

Category	Count	LEDs
User-Controllable	2	usr-led, usr-buzzer
System-Controlled	7	ACT, audio-pwr, default-on, lcd-pwr, mmc0, mmc0::, PWR
Total	9	All LEDs in the system

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Control Methods

User-Controllable LEDs

Both usr-led and usr-buzzer can be controlled using:

# Turn ON
echo 1 | sudo tee /sys/class/leds/<led-name>/brightness

# Turn OFF
echo 0 | sudo tee /sys/class/leds/<led-name>/brightness

# Check status
cat /sys/class/leds/<led-name>/brightness

System LEDs

System LEDs are typically read-only and controlled by the kernel/system. Attempting to control them may:

• Be ignored by the system
• Be overridden by system triggers
• Require disabling system triggers first (not recommended)

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Notes

1. usr-buzzer is technically a buzzer, not an LED, but uses the LED control interface
2. usr-led may not be physically visible on all reTerminal DM4 models
3. All LEDs require sudo for control (or proper udev rules/permissions)
4. System LEDs are best left to system control for proper functionality

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Quick Reference

# List all LEDs
ls /sys/class/leds/

# Check LED status
cat /sys/class/leds/<led-name>/brightness
cat /sys/class/leds/<led-name>/trigger

# Control user LEDs
echo 1 | sudo tee /sys/class/leds/usr-led/brightness      # LED ON
echo 0 | sudo tee /sys/class/leds/usr-led/brightness      # LED OFF
echo 1 | sudo tee /sys/class/leds/usr-buzzer/brightness   # Buzzer ON
echo 0 | sudo tee /sys/class/leds/usr-buzzer/brightness   # Buzzer OFF

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Related Documentation

• LED-CONTROL-GUIDE.md - Detailed LED control guide
• LED-TROUBLESHOOTING.md - Troubleshooting LED issues
• FLASK-BUZZER-CONTROL.md - Flask API for buzzer/LED control
• BUZZER-TEST-GUIDE.md - Buzzer testing guide