Flashlight UI - Distributed FreeRTOS System

This project was intended to implement an Anduril-2 based flashlight UI by ToyKeeper for testing on Texas Instrument Tiva development boards.

• Anduril-2 GitHub: https://github.com/ToyKeeper/anduril
• UI Chart: https://www.reddit.com/r/flashlight/comments/sk1upj/and%C3%BAril_2_ui_chart/

The system combining Tiva TM4C1294 (button & LED control) with Raspberry Pi 4 (FreeRTOS task scheduler). Button press → Tiva sends event → Pi4 processes with 3 tasks → Pi4 sends command → Tiva toggles LED.

Quick Start

1. Upload Tiva Firmware

cd ~\flashlight_ui
~/.platformio/penv/Scripts/platformio.exe run --target upload
# Press RESET button - blue LED should blink

2. Run Pi4 Relay

ssh raspberrypiuser@raspberrypiaddress
cd pi4-freertos
./flashlight_relay

3. Test

Press button SW1 on Tiva → Red LED toggles → Check Pi4 shows "LED_OK"

Hardware

Connection: Tiva ICDI Micro USB → Pi4 USB-A Port

Pin Mapping:

• Red LED (D1): PN_1 (toggled by Pi4)
• Green LED (D2): PN_0 (unused)
• Blue LED (D3): PF_0 (heartbeat - blinks every 1 sec)
• Button SW1: PJ_0 (sends event to Pi4)

Serial: 115200 baud, /dev/ttyACM0 (CDC ACM protocol)

PWM Brightness: Red LED (D1) supports PWM brightness control (0-255)

System Architecture

Tiva Board           Pi4 FreeRTOS Relay
├─ Button Input   → ├─ Serial Receiver Task
├─ LED Control   ← ├─ LED Controller Task
└─ Heartbeat       └─ Heartbeat Task
      ║ USB Serial ║
    /dev/ttyACM0

Features

• 3 concurrent FreeRTOS-style tasks on Pi4
• Mutex locks + Semaphore synchronization
• Pre-compiled Pi4 binary ready to run (71KB)
• Heartbeat: Double-flash every 10 seconds (low power indicator)
• PWM brightness control: 0-255 for red LED
• Simple text protocol:
  • BTN_PRESSED (Tiva → Pi4)
  • LED_TOGGLE (Pi4 → Tiva)
  • BRIGHTNESS=0-255 (Pi4 → Tiva)
  • LED_OK (acknowledgment)
• Auto buffer-clearing for clean serial communication
• Deploy to multiple Pi4s (just copy pi4-freertos/ directory)

Build Commands

# Tiva firmware
~/.platformio/penv/Scripts/platformio.exe run --target upload

# Pi4 relay (build from source)
cd pi4-freertos && make clean && make && ./flashlight_relay

# Pi4 relay (run pre-compiled)
cd pi4-freertos && ./flashlight_relay

Troubleshooting

Problem	Solution
Blue LED not blinking (heartbeat)	Re-upload firmware, press RESET button
Red LED won't toggle	Check relay is running, try holding button longer
Brightness control not working	Ensure Pi4 sends "BRIGHTNESS=X" command (0-255)
Serial data corrupted	Normal on startup, relay auto-clears buffer
Permission denied	Run with sudo or: sudo chmod 666 /dev/ttyACM0

Button Controls (Intelligent UI)

From OFF State

• 1 click: Turn ON at Level 1 (25% brightness)

From ON State (any level)

• 1 quick click: Cycle to next brightness level (1→2→3→4→1)
• Hold button (500ms+): Rapid brightness cycling (auto-increment)
• Release after hold: Stop at current brightness

Brightness Levels

• Level 1: 25% brightness
• Level 2: 50% brightness
• Level 3: 75% brightness
• Level 4: 100% brightness
• (Then wraps back to Level 1)

Quick OFF

• From any ON state: Quick 2nd click (< 250ms) after first click = Turn OFF

Files

• src/main.cpp - Tiva firmware
• pi4-freertos/flashlight_relay - Pre-compiled Pi4 binary
• pi4-freertos/flashlight_relay.c - Pi4 source code
• pi4-freertos/Makefile - Pi4 build config