Understanding the Basic RTOS Features of VxWorks: A Practical Guide for Engineers

VxWorks is a real-time operating system (RTOS) developed by Wind River, widely adopted in mission-critical embedded systems. This article will introduce the fundamental features of VxWorks, including task control, inter-process communication (IPC), signal handling, and virtual devices, along with practical code examples.

Why Choose VxWorks?

VxWorks provides a Unix-like multitasking environment with the following characteristics:

• Hard real-time performance
• Modular and scalable architecture
• POSIX compliance
• Support for symmetric/asymmetric multi-core processing (SMP/AMP)
• Rich network and file system APIs
• Support for modern processors (ARM, Intel, MIPS, etc.)

Using the host-target development model: development is done on a host (such as Linux/Windows) and deployed on embedded target boards.

⚙️ System Initialization and Configuration

The typical startup process includes setting the system clock, initializing device drivers, and starting the initial tasks.

#include <vxWorks.h>
#include <sysLib.h>
#include <taskLib.h>

void sysInit()
{
    sysClkRateSet(100);  // Set system clock frequency to 100 Hz
}

👷 Task Management

Tasks in VxWorks are similar to threads and have independent states: ready, running, suspended, etc.

Creating and Starting Tasks

void myWorker()
{
    while (1)
    {
        printf("Task is running\n");
        taskDelay(100);  // 1 second delay (if clock frequency is 100Hz)
    }
}

void startTask()
{
    int tid = taskSpawn("tWorker", 100, 0, 8192, (FUNCPTR)myWorker, 0,0,0,0,0,0,0,0,0,0);
    if (tid == ERROR)
        perror("taskSpawn failed");
}

Suspending and Resuming Tasks

void pauseTask(int tid)
{
    taskSuspend(tid);
}

void resumeTask(int tid)
{
    taskResume(tid);
}

🔁 Inter-Process Communication (IPC)

1. Semaphores

Used for mutual exclusion and task synchronization.

Binary Semaphore Example

#include <semLib.h>

SEM_ID sem;

void initSem()
{
    sem = semBCreate(SEM_Q_PRIORITY, SEM_EMPTY);
}

void taskUsingResource()
{
    semTake(sem, WAIT_FOREVER);
    // Critical section
    semGive(sem);
}

Mutex (Supports Priority Inheritance)

SEM_ID mutex = semMCreate(SEM_Q_PRIORITY | SEM_INVERSION_SAFE);

2. Message Queues

Supports structured, FIFO, or priority-based message passing.

#include <msgQLib.h>

MSG_Q_ID msgQ;

void setupQueue()
{
    msgQ = msgQCreate(10, sizeof(int), MSG_Q_PRIORITY);
}

void producer()
{
    int value = 123;
    msgQSend(msgQ, (char*)&value, sizeof(int), WAIT_FOREVER, MSG_PRI_NORMAL);
}

void consumer()
{
    int rcv;
    msgQReceive(msgQ, (char*)&rcv, sizeof(int), WAIT_FOREVER);
    printf("Received: %d\n", rcv);
}

⚡ Signal Handling (Software Interrupts)

Signals are used for asynchronous notifications.

#include <signal.h>
#include <sigLib.h>

void signalHandler(int sigNum)
{
    printf("Received signal %d\n", sigNum);
}

void setupSignal()
{
    sigset(SIGUSR1, signalHandler);
    kill(taskIdSelf(), SIGUSR1);  // Send signal to self
}

💻 Virtual Devices

Pipes and network sockets are similar to file descriptors.

Pipes as I/O Channels

#include <ioLib.h>
#include <pipeDrv.h>

void setupPipe()
{
    pipeDevCreate("/pipe/test", 1024, 1024);
    int fd = open("/pipe/test", O_RDWR, 0);

    write(fd, "hello", 5);
    char buffer[6] = {0};
    read(fd, buffer, 5);
    printf("Received: %s\n", buffer);
}

🌐 Basic Network Functionality

VxWorks supports the BSD socket API, compatible with IPv4 and IPv6.

#include <sockLib.h>
#include <inetLib.h>
#include <netinet/in.h>

void openSocket()
{
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    // bind, listen, connect, etc.
}

📁 File System API Example

Using RAM Disk:

#include <ramDrv.h>
#include <dosFsLib.h>
#include <ioLib.h>

void setupRamDisk()
{
    ramDevCreate("/ram0", 512, 100);  // Create 100 blocks of 512 bytes RAM disk
    dosFsVolFormat("/ram0", DOS_OPT_BLANK, NULL);

    int fd = open("/ram0/file.txt", O_CREAT | O_RDWR, 0666);
    write(fd, "VxWorks", 7);
    close(fd);
}

📚 Common Header Files

Header File	Description
`<span>vxWorks.h</span>`	Core definitions
`<span>taskLib.h</span>`	Task control API
`<span>semLib.h</span>`	Semaphore functions
`<span>msgQLib.h</span>`	Message queues
`<span>sigLib.h</span>`	Signal handling interfaces
`<span>pipeDrv.h</span>`	Pipe device driver
`<span>inetLib.h</span>`	Network address and protocol tools

🔒 Security Features

• Priority Inheritance mechanism
• Task Deletion Protection
• Watchdog Timer
• Virtual Memory and MMU Support
• Power Management Interfaces

✅ Conclusion

VxWorks provides powerful task control, synchronization mechanisms, and modular I/O support. This article focused on the following topics:

• Managing tasks using taskSpawn, taskSuspend, and taskResume
• Implementing inter-task communication using semaphores and message queues
• Using pipes and sockets for modular device communication
• Signal mechanisms for asynchronous event handling
• Extended functionalities including power management, file systems, and network protocol stacks

Mastering these interfaces can help engineers build reliable and responsive embedded applications.

📎 References

• Wind River VxWorks Official Documentation
• VxWorks 6 Online Documentation