Event Monitor Module

Overview

This project implementing a firmware module that counts GPIO input events triggered by an interrupt, filters them using bit manipulation (rising edges), and communicates the count to a task running under an RTOS.

• Detects rising edges on specified GPIO pins.
• Counts events in an thread-safe way.
• Periodically reports the event count from an RTOS task.

Files

• event_monitor.h/c: Event monitoring implementation.
• test_event_monitor.c: Unit tests for edge detection and event filtering.
• gpio_hal.h/c : Header file and dummy implementations of custom hal api.
• rtos_api.h/c : Header file and dummy implementations of rtos api.
• Makefile: build file if using make.
• README.md: This document.

Design Details

Rising Edge Detection

Rising edges are detected by comparing the previous GPIO state with the current one. The transition 0 -> 1 is identified using bit manipulation:

rising_edges = (~gpio_state & new_state) & gpio_pin_mask;

Explanation:

• `~gpio_state negates the current state, which will give us value 1 on pins that were low.
• ~gpio_state & new_state identifies bits that transitioned from 0 to 1.
• & gpio_pin_mask ensures only configured pins are counted.

Example: only bit 0 was high in previous state, so gpio_state is 0x00000001. Negating it gives us 0xFFFFFFFE. If the new state is 0x00000003 ~gpio_state & new_state wil give us result 0x00000002. This means that GPIO1 has a rising edge and counter should be increased by 1. If the given mask is including GPIO1 counter will be increased by 1.

Interrupt Safety

• The event counter is shared between the interrupt handler and the RTOS task.
• Access to the counter is guarded by rtos_mutex_lock() and rtos_mutex_unlock().

RTOS Task

• A periodic task runs every 1000 ms.
• It reads and resets the event count.
• The count is passed to report_event_count(uint32_t count).

Stubbed Function

void report_event_count(uint32_t count);

The stubbed implementation of this function transmiting the counter to global variable which can be used in unit tests.

Build Instructions

Build

The project is created in Microsoft Visual Studio Code using command prompt and gcc compiler. Compile with:

gcc -Iinclude src/event_monitor.c src/gpio_hal.c src/rtos_api.c test/test_event_monitor.c -o test_event_monitor.exe

or alternatively use make command with provided Makefile. If some other terminal is used, clean command should be changed accordingly.

Running

./test_event_monitor.exe

Testing

• Edge detection and filtering are tested in isolation.
• Simulated GPIO changes validate correct counting logic.

Notes

• This implementation is designed for a cooperative RTOS and uses mutexes to protect shared data.
• event_monitor_init() must be called during initialization.
• GPIO callbacks and state transitions are simulated for testing.

Limitations

• Actual GPIO ISR timing and latency are not simulated in tests.
• Real hardware timing may vary and should be validated on target.

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Author: Vladimir Medic Date: 19.06.2025.