undoBUS In Development

Fieldbus master implementations for the undoRT ecosystem — built on undoCore's IoBus interface.

Overview

undoBUS provides fieldbus master implementations that integrate seamlessly with the undoRT ecosystem. Built on the IoBus interface defined in undoCore, undoBUS will offer deterministic, real-time fieldbus communication for industrial automation.

Architecture

undoBUS follows the IoBus synchronization protocol defined in undoCore:

/**
 * Synchronization protocol:
 *
 *   [Bus]  cycleStart()  → copyIn() → notifyPlc()
 *   [PLC]                                          → execute() → notifyBus()
 *   [Bus]  copyOut() → sendFrame()
 */

Core Components

EtherCAT

The first fieldbus protocol to be supported by undoBUS is EtherCAT, using the IgH EtherCAT Master as the underlying stack.

Key Features (Planned)

• Real-time user-space operation
• Process Image mapping via undoCore::ProcessImage
• Distributed Clock (DC) synchronization
• Hot-connect / dynamic PDO mapping
• Diagnostic counters and error reporting
• Watchdog with safe-state handling

Anticipated API

#include 
#include 

using namespace undoCore;
using namespace undoBUS;

// 1024 inputs, 512 outputs
ProcessImage<1024, 512> pi;

// Configure and start EtherCAT master
EtherCATMaster bus("eth0", "/path/to/eni.xml", pi);
bus.start();

// PLC cycle — bus drives the timing
while (running) {
    // Bus waits for cycle and copies inputs (copyIn)
    if (!bus.waitCycle(1000)) {
        // Watchdog timeout
        break;
    }

    // PLC executes user logic (reads from pi, writes to pi)
    plc.run();

    // Notify bus that PLC is done
    bus.notifyDone();  // bus calls copyOut() and sends frame
}

Profibus

Profibus DP master support is planned as a future extension. The implementation will follow the same IoBus contract, ensuring protocol-agnostic integration with undoPLC.

Other Protocols

Additional fieldbus protocols are under evaluation based on community interest and industrial demand. Potential candidates include:

• • PROFINET — Industrial Ethernet standard
• • Modbus TCP/RTU — Widely used serial protocol
• • CANopen — CAN-based fieldbus
• • EtherNet/IP — ODVA industrial protocol

Integration with undoCore

undoBUS is built on undoCore, using:

• IoBus — Abstract interface for all fieldbus masters
• ProcessImage — Double-buffered memory layout for I/O
• types.hpp — IEC 61131-3 type mapping

#include 

class EtherCATMaster : public IoBus {
    // Implements all IoBus virtual methods
    // Uses ProcessImage for I/O mapping
};

Integration with undoPLC

undoPLC consumes the IoBus interface, making it completely agnostic to the underlying fieldbus protocol:

// In undoPLC MasterTask
class DemoMasterTask : public UndoMasterTaskBase {
protected:
    void readInputBus() override {
        // Bus waits for cycle and copies inputs
        if (!_bus->waitCycle(1000)) {
            // Watchdog timeout
            handleWatchdog();
        }
    }

    void writeOutputBus() override {
        // Bus copies outputs and sends frame
        _bus->notifyDone();
    }
};

Roadmap

API Reference

Full API documentation will be generated with Doxygen when the first release is available: Browse API Reference