Device Engine (Reference)

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Operating Architecture

Module Initialization

At startup, the Device Engine:

1. Identifies configured protocol drivers
2. Creates optimized communication groups based on:
   • Operand Type - Bits, words, registers, blocks
   • AccessType - Read, Write, or ReadWrite
   • Scan Intervals - Polling time configuration
   • Protocol Limits - Size and quantity constraints

This grouping optimizes performance and ensures protocol compliance.

Communication Groups

Groups are organized by:

• Common data types
• Similar polling rates
• Access patterns
• Protocol specifications

Execution Model

Communication Triggers

Thread Architecture

Event Queue Processing:

1. Triggers place events in execution queue
2. Central thread scans queue every 20ms
3. Events assigned to independent threads
4. Parallel execution without blocking

Benefits:

• Low latency response
• Fault isolation between groups
• Efficient multicore utilization
• Non-blocking operations

Communication Flow

Execution Sequence

1. Group Activation - Thread receives communication task
2. Message Generation - TX packet created per protocol
3. Connection Management - Open/reuse TCP, UDP, or Serial
4. Data Exchange - Send request, await response
5. Value Mapping - Update tags with received data
6. Error Handling - Retry logic and diagnostics

Read Operations

Device → Protocol Driver → Tags
1. Build read request
2. Send to device
3. Receive response
4. Parse data
5. Update tag values

Write Operations

Tags → Protocol Driver → Device
1. Collect tag values
2. Build write request
3. Send to device
4. Await confirmation
5. Update status

Module Responsibilities

The Device Engine manages:

• Protocol Management - Driver lifecycle and configuration
• Group Creation - Optimal communication grouping
• Trigger Definition - Time and event-based execution
• Thread Scheduling - Independent thread allocation
• Data Routing - Tag-to-device value mapping
• Diagnostics - Performance and status monitoring

Diagnostics and Monitoring

Performance Metrics

Status Indicators

• Connection state (Active/Failed/Reconnecting)
• Last communication timestamp
• Error counts and types
• Retry attempts
• Data quality

Configuration Guidelines

Group Optimization

Optimal Group Size:
- Modbus: 100-125 registers
- OPC UA: 500-1000 items
- Ethernet/IP: 400-500 bytes

Thread Pool Sizing

Threads = min(CPU_Cores * 2, Active_Groups)
Queue Size = Active_Groups * 2
Scan Rate = 20ms (default)

Error Handling

Retry Strategies

Fault Isolation

• Thread failures don't affect other groups
• Connection issues isolated per channel
• Protocol errors logged per driver
• Graceful degradation on partial failures

Performance Tuning

Reducing Latency

• Decrease scan interval
• Optimize group sizes
• Use event-driven triggers
• Enable connection pooling

Improving Throughput

• Increase thread pool
• Combine read operations
• Use block transfers
• Enable compression

Resource Optimization

• Share connections
• Cache static data
• Filter unchanged values
• Implement deadbands

Best Practices Checklist

• Group Similar Points - Same data type and polling rate
• Balance Group Sizes - Respect protocol limits
• Stagger Polling - Distribute communication load
• Monitor Cycle Times - Identify bottlenecks
• Use Event Triggers - For write operations
• Enable Diagnostics - Track performance
• Configure Timeouts - Match network conditions

Troubleshooting

High Cycle Times:

• Check network latency
• Reduce group size
• Increase thread pool
• Review timeout settings

Communication Failures:

• Verify device connectivity
• Check protocol settings
• Review error logs
• Test with smaller groups

Queue Overflow:

• Increase thread count
• Reduce polling rates
• Optimize group sizes
• Check for blocking operations

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