Applications of C Language in Embedded Systems: Hardware Interface Programming

Introduction

The C language is a widely used programming language, especially significant in embedded system development. Its efficiency and direct control over hardware make C the preferred choice for embedded developers. In this article, we will explore how to use C for hardware interface programming and demonstrate basic operations through example code.

Overview of Hardware Interfaces

In embedded systems, a hardware interface refers to the communication methods between microcontrollers and external devices (such as sensors, actuators, etc.). Common hardware interfaces include:

• GPIO (General Purpose Input/Output)
• I2C (Inter-Integrated Circuit)
• SPI (Serial Peripheral Interface)
• UART (Universal Asynchronous Receiver-Transmitter)

We will focus on the two common hardware interfaces: GPIO and I2C.

GPIO Programming

What is GPIO?

GPIO is a pin that can be configured as either input or output mode. By setting the pin state, data interaction with other devices can be achieved. For example, setting a pin to a high level can light up an LED.

Example: Controlling an LED

Below is a simple example demonstrating how to control an LED connected to a GPIO pin using C language.

#include <stdio.h>
#include <stdlib.h>
#include <wiringPi.h>
#define LED_PIN 0 // Define LED connected to WiringPi pin number 0
int main() {    // Initialize WiringPi library    if (wiringPiSetup() == -1) {        printf("Initialization failed!\n");        return 1;    }
    pinMode(LED_PIN, OUTPUT); // Set pin to output mode
    while (1) {        digitalWrite(LED_PIN, HIGH); // Light up LED        delay(1000);                  // Delay 1 second        digitalWrite(LED_PIN, LOW);  // Turn off LED        delay(1000);                  // Delay 1 second    }
    return 0;}

Code Analysis

1. Library Inclusion: We use the <span>wiringPi</span> library to simplify GPIO operations.
2. Initialization: Call the <span>wiringPiSetup()</span> function for initialization; if it fails, an error message is returned.
3. Setting Mode: Use the <span>pinMode()</span> function to set the specified pin to output mode.
4. Loop Control: In an infinite loop, use the <span>digitalWrite()</span> function to change the pin state, achieving the lighting and extinguishing of the LED, with a delay of one second each time.

I2C Programming

What is I2C?

I2C is a serial bus protocol used for short-distance communication, typically for connecting low-speed devices such as sensors and EEPROMs. It supports multi-master and multi-slave architectures, making it suitable for data exchange between multiple components in complex systems.

Example: Reading Temperature Sensor Data

Below is an example program for reading data from a temperature sensor connected to the I2C bus.

#include <stdio.h>
#include <stdlib.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#define I2C_DEVICE "/dev/i2c-1"   // I2C device file path
#define TEMP_SENSOR_ADDR 0x48      // Temperature sensor address
int main() {    int file;
    if ((file = open(I2C_DEVICE, O_RDWR)) < 0) {        perror("Failed to open I2C device");        exit(1);    }
    if (ioctl(file, I2C_SLAVE, TEMP_SENSOR_ADDR) < 0) {        perror("Failed to set slave address");        exit(1);    }
    char buf[3];
    while (1) {        if (read(file, buf, 3) != 3) {             perror("Failed to read data");            exit(1);        }
        int temp = ((buf[0] << 8) | buf[1]) >> 4;         float temperature = temp * 0.0625; 
        printf("Current Temperature: %.4f °C\n", temperature);
        sleep(1);     }
    close(file);
    return 0;}

Code Analysis

1. Opening I2C Device: First, we open the corresponding I2C device file. If opening fails, an error message is printed, and the program exits.

2. Setting Slave Address: Using the <span>ioctl()</span> function, we set the target temperature sensor address as the current active slave, allowing subsequent read and write operations to proceed correctly.

3. Reading Data:

• Use the <span>read()</span> function to read data from the temperature sensor, assuming three bytes of data are returned.
• Convert the received data into the actual temperature value and print it. Here, it is assumed that each unit represents a part of a degree Celsius, and the calculation formula should be adjusted according to the specific chip manual.

Looping to Get Data: The program continuously retrieves the temperature every second and displays the result.

Conclusion

This article introduced how to utilize the C language for basic hardware interface programming in embedded systems, including applications of GPIO and I²C. These foundational concepts are crucial for beginners to understand embedded development, and we hope they help you better master related skills. In actual projects, you can expand these basic functions according to your needs to implement more complex and interesting software applications.