PCI-Based CAN Card Design and VxWorks Driver Development

PCI-Based CAN Card Design and VxWorks Driver Development

This article presents a practical implementation of a PCI-based CAN interface card and its corresponding driver under the VxWorks real-time operating system. The design targets high-reliability embedded systems, such as vehicle-mounted virtual instruments, where deterministic communication and robust hardware integration are essential.

🧭 System Overview and Design Goals

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In integrated vehicle electronic systems, CAN bus serves as the backbone for communication between control and measurement modules. The display terminal must:

• Collect real-time data from CAN nodes
• Process and visualize system parameters
• Support command transmission and storage

To meet these requirements:

• PCI/CompactPCI-based embedded platforms are used
• VxWorks RTOS ensures deterministic scheduling and reliability
• A custom PCI CAN interface card enables CAN connectivity

🔌 Hardware Architecture of the PCI CAN Card

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The design leverages a bridge-based architecture to simplify PCI integration.

Core Components

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• PLX PCI9052 — PCI bridge controller
• SJA1000 — CAN controller
• 82C250 — CAN transceiver
• 93LC46B EEPROM — configuration storage
• CPLD (EPM7064S) — glue logic and signal control

⚙️ PCI9052 and PCI Bus Integration

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The PCI9052 operates in ISA mode, which simplifies local bus interfacing:

• PCI interface connects directly to the host bus
• Local bus emulates ISA timing and signaling
• EEPROM stores:
  • Vendor ID / Device ID
  • Base Address Registers (BARs)

At system boot, the PCI9052 loads configuration from EEPROM, enabling automatic resource allocation.

🔗 PCI9052 and SJA1000 Interface

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Key signal connections:

• BALE → ALE (address latch)
• LAD[15:0] → 8-bit data bus
• Address decoding via LA[23:2] and ISAA[1:0]
• CLKOUT (SJA1000) → LCLK (PCI9052)
• LRESET → reset logic (via CPLD)
• INT → LINTi1 (interrupt line)

Design Notes

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• CPLD handles:
  • Address/data multiplexing
  • Reset polarity adjustment
• Control signals (LRDY, CHRDY, etc.) are configured for timing compliance

🌐 CAN Physical Layer

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The 82C250 transceiver provides:

• Differential signaling (CANH/CANL)
• High-speed mode configuration
• Bus protection

Standard 120 Ω termination resistors ensure signal integrity.

🧠 VxWorks Software Architecture

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The software stack consists of two layers:

1. PCI device driver — handles resource discovery and mapping
2. CAN device driver — manages communication and protocol interaction

🧩 PCI Device Initialization

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The driver identifies the device and retrieves assigned resources:

if (pciFindDevice(CAN_VENDOR_ID, CAN_DEVICE_ID, 0,
                  &busNo, &deviceNo, &funcNo) == ERROR) {
    printf("Cannot find the CAN card\n");
    return ERROR;
}

pciConfigInLong(busNo, deviceNo, funcNo, PCI_CFG_BASE_ADDRESS_0, &membaseCsr);
pciConfigInLong(busNo, deviceNo, funcNo, PCI_CFG_BASE_ADDRESS_1, &iobaseCsr);
pciConfigInByte(busNo, deviceNo, funcNo, PCI_CFG_DEV_INT_LINE, &irq);

Memory Mapping

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sysMmuMapAdd(...);

This ensures that device registers are accessible in the system address space.

🚦 CAN Driver Implementation

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The CAN driver follows the VxWorks I/O model and implements:

• canOpen()
• canClose()
• canRead()
• canWrite()
• canIoctl()

Device Abstractions

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• CAN_DEV — device descriptor
• CAN_CHAN — communication channel and callback interface

Initialization (canOpen)

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• Configure SJA1000:

  • Baud rate
  • Acceptance filters
  • Operating mode

Data Flow

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• canWrite() queues outgoing frames
• canRead() retrieves received data via callbacks

⚡ Interrupt Handling and Data Processing

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Interrupt-driven design ensures real-time responsiveness.

Driver Setup

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canDrvNum = iosDrvInstall(...);
pciIntConnect(..., can_interrupt, ...);
sysIntEnablePIC(irq);

ISR Design

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void can_interrupt(void) {
    // Handle RX/TX events
    // Trigger callbacks
}

Callback Mechanism

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CanCallbackInstall(...);

Benefits:

• Decouples hardware layer from application logic
• Enables flexible protocol integration
• Reduces ISR workload

🧪 Testing and Validation

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Hardware Verification

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• PCI device detected correctly by BIOS
• Basic CAN communication verified under Windows

VxWorks Testing

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• Driver loaded successfully
• Separate read/write tasks implemented
• Stable communication with external CAN node

Results

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• Continuous frame transmission (100 ms interval)
• No data loss observed
• Deterministic system behavior achieved

🏭 Practical Design Considerations

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Reliability

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• Proper interrupt configuration
• Stable EEPROM initialization
• Robust physical layer design

Performance

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• Use interrupt-driven I/O instead of polling
• Minimize ISR execution time
• Optimize buffer and queue management

Scalability

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• Modular driver structure supports extension
• Callback mechanism enables protocol layering

📌 Conclusion

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The PCI-based CAN interface card combined with a VxWorks driver provides a reliable solution for real-time embedded communication systems.

Key takeaways:

• PCI9052 simplifies PCI integration without additional MCU
• SJA1000 offers flexible and efficient CAN control
• VxWorks enables deterministic interrupt handling and task coordination
• Callback-based driver design improves modularity and scalability

This architecture is well-suited for high-reliability domains such as automotive, industrial control, and defense systems.