Task Monitor RTOS (Bare-Metal, No Libraries)

This project implements a cooperative real-time operating system (RTOS) on an STM32F4 microcontroller without using any external libraries (no HAL, no CMSIS). It serves as a task monitor system, displaying real-time information about task execution, system health, and live sensor data on an LCD1602 display.

Overview

The system runs fully on bare-metal C and demonstrates the following:

• Cooperative task scheduler (non-preemptive)
• LCD1602 interface via GPIO (4-bit mode, with busy flag checking)
• UART logging interface using direct register access
• Push-button handling with debouncing
• DHT11 temperature/humidity sensor integration via single-wire protocol
• Real-time task monitoring with dynamic LCD updates

Features

DEMO

RTOS (Bare-Metal)

• Custom task structure with delay, ready, and func fields
• Round-robin execution model
• SysTick-based timing (1 ms granularity)
• Per-task counters and delay management

LCD Task Monitor

• Displays two tasks per screen refresh:
  • Task ID
  • Run count
  • Delay (ms)
• Automatically rotates through tasks every second
• Dedicated display for DHT11 sensor readings (temp/humidity)

UART Debug Logging

• Fully manual UART2 driver (PA2, 115200 baud)
• Real-time logging of system events, sensor readings, and errors
• Serial monitor supported via USB/TTL serial adapter

DHT11 Integration

• Bit-banged single-wire protocol
• Pulse-width-based decoding of 40-bit transmission
• Data validation via checksum
• Live display of humidity and temperature

Button-Triggered Events

• GPIO input on PA9
• On press, resets task run counters and logs event over UART
• Flag-driven signaling to prevent race conditions

Hardware

• MCU: STM32F446RE (or compatible STM32F4)
• Display: LCD1602 (parallel interface, 4-bit)
• Sensor: DHT11 temperature/humidity sensor
• Interface: USB UART (TTL serial, 115200 baud)
• Button: Connected to PA9 for reset trigger

Build & Flash

Assumes arm-none-eabi-gcc toolchain is installed.

make
st-flash write build/main.bin 0x8000000

Project Goals

This project was built as a hands-on exercise in:

• Understanding low-level peripheral control on ARM Cortex-M
• Writing a custom scheduler without relying on CMSIS or HAL
• Building scalable embedded software from scratch
• Interfacing with real-world sensors and displays using strict timing

Future Improvements

• Add I2C or SPI peripherals
• Task priority handling
• Preemptive scheduling
• Low-power sleep mode
• External EEPROM logging