C++ Embedded Development: Hardware Interfaces and Real-Time Programming

In today’s rapidly evolving technological environment, embedded systems have become a core component of many electronic products. C++, as a powerful programming language, is increasingly favored in the field of embedded development due to its object-oriented features. In this article, we will explore how to use C++ for embedded development, specifically focusing on hardware interfaces and real-time programming.

Hardware Interfaces

Hardware interfaces refer to the methods by which software interacts with hardware. By manipulating interfaces such as GPIO (General Purpose Input/Output), serial communication (like UART, SPI, I2C), etc., programs can control external devices such as sensors and motors.

1. GPIO Control Example

GPIO is one of the most common hardware interfaces. In the following code example, we demonstrate how to use C++ to control the lighting and extinguishing of an LED.

#include <iostream>
#include <wiringPi.h>
#define LED_PIN 0 // Assume LED is connected to GPIO0
void setup() {    wiringPiSetup(); // Initialize WiringPi library    pinMode(LED_PIN, OUTPUT); // Set LED_PIN to output mode}
void loop() {    digitalWrite(LED_PIN, HIGH); // Turn on LED    delay(1000);                  // Delay 1 second    digitalWrite(LED_PIN, LOW);  // Turn off LED    delay(1000);                  // Delay 1 second }
int main() {    setup();
    while(true) {        loop();    }
    return 0;}

Code Explanation:

• wiringPi Library: A software library that simplifies GPIO operations on Raspberry Pi.
• <span>pinMode</span> function sets the specified pin as input or output.
• <span>digitalWrite</span> function controls the state of the corresponding pin based on the provided state (high/low).
• <span>delay</span> function implements a delay feature, causing the LED to blink once every second through a loop.

Serial Communication Protocol

In addition to directly manipulating GPIO, mastering serial communication protocols is also a crucial step. Below, we use the I2C protocol as an example to demonstrate how to read data from a temperature sensor.

#include <Wire.h>
#include <Arduino.h>
#define SENSOR_ADDRESS 0x48   // Temperature sensor address
float readTemperature() {     Wire.requestFrom(SENSOR_ADDRESS, 2);     int16_t rawData = (Wire.read() << 8) | Wire.read();      return rawData * 0.0625;   // Calculate temperature value based on sensor specifications}
void setup() {     Serial.begin(9600);     Wire.begin();               // Initialize I2C bus  }
void loop() {     float temperature = readTemperature();     Serial.print("Temperature: ");     Serial.println(temperature);
     delay(2000);                // Read temperature data every two seconds }
int main(){      setup();
      while(true){          loop();      }
      return 0;}

Code Explanation:

• Wire Library: An important library for I2C bus programming in Arduino.
• <span>Wire.requestFrom(SENSOR_ADDRESS, count)</span> requests data from the device; here we request two bytes of data.
• Then, we combine the two bytes to obtain the raw data through bit shifting and bitwise OR operations, and convert it to temperature value based on the corresponding formula.

Overview of Real-Time Programming

In embedded applications, achieving real-time requirements is crucial for the system. Real-time systems can generally be classified into soft real-time and hard real-time. Soft real-time allows for a certain degree of time delay, while hard real-time must ensure that tasks are completed strictly on time.

Implementation Strategies

In practical applications, priority scheduling mechanisms can be utilized to manage the execution order and time intervals of tasks. For example, with the support of RTOS (Real-Time Operating System), we can create multiple threads or tasks that can run at different priorities to meet various demand scenarios. For instance:

#include <iostream>
#include "FreeRTOS.h"
#include "task.h"
void taskA(void *pvParameters) {   for(;;) {        std::cout << "Task A is running" << std::endl;        vTaskDelay(pdMS_TO_TICKS(500));      }}
void taskB(void *pvParameters) {   for (;;) {        std::cout << "Task B is running" << std::endl;        vTaskDelay(pdMS_TO_TICKS(100));     }}
int main() {      xTaskCreate(taskA, "Task A", configMINIMAL_STACK_SIZE, NULL, 1, NULL);   xTaskCreate(taskB, "Task B", configMINIMAL_STACK_SIZE, NULL, 2, NULL);
   vTaskStartScheduler(); 
   for (;;) {};             
   return 0;}

Summary:

The above code demonstrates how to create two tasks with different priorities based on FreeRTOS. By calling vTaskDelay, we can configure the running intervals of each task appropriately, thus achieving cooperative resource sharing and optimizing response time. This is one of the means to ensure that software maintains a certain timeliness under constraints.

Conclusion

This article introduced some fundamental knowledge about C++ embedded development that users need to understand, including GPIO operations, serial communication, and basic practical RTOS application models. This is just the beginning, and we hope to inspire you to delve deeper into learning more related technologies and continuously expand your skill set.