VxWorks Serial Communication Design and Implementation Guide

VxWorks Serial Communication Design and Implementation Guide

Serial communication remains a fundamental mechanism for data exchange in embedded systems, especially in environments requiring reliability and deterministic behavior. VxWorks provides a robust and flexible framework for implementing serial interfaces through its I/O subsystem and driver model.

This article presents the design principles, system configuration, and practical implementation of serial communication in VxWorks, based on real-world embedded applications.

⚙️ VxWorks Architecture for Serial Communication

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VxWorks implements serial communication through a layered driver architecture:

Core Components

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• Serial Communication Controller (SCC)
  Hardware-level interface supporting multiple serial channels

• SCC Driver
  Handles low-level hardware operations and interrupt management

• tty Driver
  Provides a unified character device interface for applications

• I/O System
  Abstracts device access using standard file operations (open, read, write)

This separation enables portability and simplifies application-level development.

🔌 Serial Device Model in VxWorks

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Serial ports are exposed as character devices, typically in the form:

/tyCo/x

Where:

• tyCo represents the tty device class
• x is the channel index (e.g., /tyCo/0 for COM1)

tty Driver Modes

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• RAW Mode (default)

  • Direct byte stream
  • No buffering or line editing

• LINE Mode

  • Line-based input processing
  • Includes editing and buffering

RAW mode is preferred for real-time embedded communication due to minimal overhead.

🧠 Communication Modes and Considerations

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Interrupt vs Polling

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• Interrupt-driven mode

  • Efficient for high-throughput or asynchronous communication
  • Lower CPU usage

• Polling mode

  • Simpler but less efficient
  • Suitable for low-frequency communication

Non-Blocking I/O

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To avoid blocking on slow devices, VxWorks supports:

• select() for I/O multiplexing
• Asynchronous I/O (AIO)
• Timeout-based reads

These mechanisms are critical in real-time systems where blocking can violate timing constraints.

🛠️ System Configuration

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BSP Configuration

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To enable serial communication and debugging:

• Modify config.h in the BSP
• Enable serial-based debugging (WDB) if required

Build and Deployment

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Typical steps include:

1. Build Boot ROM and VxWorks image
2. Generate boot media (e.g., via mkboot)
3. Boot target hardware and load the RTOS

This setup ensures the serial interface is initialized during system startup.

💻 Serial Communication Example

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Include Required Headers

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#include <VxWorks.h>
#include <ioLib.h>
#include <fioLib.h>
#include <tyLib.h>
#include <selectLib.h>
#include <stdio.h>
#include <ioctl.h>

Open Serial Port

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int sfd = open("/tyCo/0", O_RDWR, 0);

Configure Serial Parameters

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ioctl(sfd, FIOSETOPTIONS, OPT_RAW);   // RAW mode
ioctl(sfd, FIOBAUDRATE, 9600);        // Baud rate
ioctl(sfd, FIOFLUSH, 0);              // Clear buffers

Receive Data (Non-Blocking with select)

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fd_set fds;

while (1) {
    FD_ZERO(&fds);
    FD_SET(sfd, &fds);

    if (select(sfd + 1, &fds, NULL, NULL, NULL) == ERROR)
        return ERROR;

    read(sfd, recv_buf, sizeof(recv_buf));
}

Send Data

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fd_set fds_write;

FD_SET(sfd, &fds_write);

if (select(sfd + 1, NULL, &fds_write, NULL, NULL) == ERROR)
    return ERROR;

write(sfd, send_buf, sizeof(send_buf));

Close Serial Port

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close(sfd);

⏱️ Real-Time Design Considerations

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When implementing serial communication in VxWorks:

• Avoid Blocking Calls Use select() or timeouts to maintain responsiveness

• Minimize ISR Workload Keep interrupt handlers short and defer processing to tasks

• Buffer Management Ensure sufficient buffering for burst data

• Error Handling Detect and recover from communication faults (timeouts, framing errors)

🧾 Conclusion

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VxWorks provides a mature and efficient framework for serial communication through its layered driver model and flexible I/O system. By leveraging tty devices, ioctl-based configuration, and non-blocking I/O mechanisms, developers can implement reliable and deterministic serial interfaces.

This approach is well-suited for embedded applications such as industrial control and defense systems, where stable communication and real-time performance are essential.