undoBUS In Development

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

Overview

undoBUS provides fieldbus master implementations for the undoRT ecosystem. Built on the IoBus interface defined in undoCore, undoBUS is intended to provide 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 <undoBUS/EtherCATMaster.hpp>
#include <undoCore/undoCore.hpp>

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 builds 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 <undoCore/undoCore.hpp>

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

undoBUS has no release yet, so there is no API reference to link to. The repository currently holds the project skeleton and nothing else.