Project Initialization

Assuming the wiringOP library is already installed on the system, the first step involves creating a dedicated workspace for the source code and binaries. Execute the following commands to create a directory named embedded_drivers and initialize a C source file:

mkdir embedded_drivers
cd embedded_drivers
vim gpio_control.c

Core API Functions

Interaction with the general-purpose input/output (GPIO) pins requires three primary functions provided by the library. Before any pin operations can occur, the library must be initialized.

• wiringPiSetup(void): This function initializes the wiringPi system. It must be called before any other GPIO operations. It returns an integer status code, where -1 indicates failure to initialize.
• pinMode(int pin, int mode): Configures the behavior of a specific pin. The mode parameter accepts constants such as INPUT, OUTPUT, or PWM_OUTPUT to determine how the pin is utilized.
• digitalWrite(int pin, int value): Sets the logic level of a pin configured as an output. Valid values for value are HIGH (1) or LOW (0). Note that hardware configurations, such as active-low LEDs, will invert the visible effect of these logic states.

Implementation Example

The following C program demonstrates the setup and control sequence. It utilizes wiringPi pin numbering (e.g., wPi pin 0). The example assumes an active-low LED connected to the pin, meaning writing LOW will illuminate the diode.

#include <stdio.h>
#include <wiringPi.h>
#include <unistd.h> // for sleep/delay

#define STATUS_LED 0  // WiringPi Pin 0

int main(void) {
    // Initialize the wiringPi library
    if (wiringPiSetup() == -1) {
        printf("Initialization failed.\n");
        return 1;
    }

    // Configure the pin as an output
    pinMode(STATUS_LED, OUTPUT);

    // Toggle the LED state
    for (int i = 0; i < 5; i++) {
        digitalWrite(STATUS_LED, LOW);  // Turn LED ON (Active Low)
        delay(500);                      // Wait 500ms
        digitalWrite(STATUS_LED, HIGH); // Turn LED OFF
        delay(500);                      // Wait 500ms
    }

    return 0;
}