Multi-Host Modbus Client

This client application simultaneously polls multiple Modbus hosts, each with their own register configurations and polling intervals.

Features

• Connect to multiple Modbus hosts simultaneously
• Individual configuration per host (timeout, interval, registers)
• Parallel polling with unique settings for each host
• Detailed per-host result display with timing information
• Graceful error handling for connection issues
• Enable/disable individual hosts
• Comprehensive logging and result aggregation

Building

To build the client:

go build -o modbus-client main.go

Running

Basic Usage

./modbus-client --config multi-host-config.json

Command-line Options

• --config: Path to JSON configuration file (default: multi-host-config.json)
• --cycles: Number of polling cycles (default: 10, 0 for infinite)
• --single: Run only once then exit
• --log: Log to file instead of stdout

Examples

# Poll multiple hosts continuously
./modbus-client --cycles 0

# Single poll and exit
./modbus-client --single

# Log to file
./modbus-client --log modbus-client.log

# Use custom config file
./modbus-client --config custom-config.json

Configuration File

The client uses a JSON configuration file to define multiple hosts and their registers:

{
  "hosts": [
    {
      "name": "Main Controller",
      "host": "localhost",
      "port": 502,
      "unit_id": 1,
      "timeout": "5s",
      "interval": "1s",
      "enabled": true,
      "registers": [
        {
          "name": "Emergency Stop",
          "address": 10001,
          "type": "coil",
          "min_value": 0,
          "max_value": 1
        }
      ]
    },
    {
      "name": "Sensor Panel",
      "host": "192.168.1.100",
      "port": 502,
      "unit_id": 1,
      "timeout": "3s",
      "interval": "500ms",
      "enabled": true,
      "registers": []
    }
  ]
}

Host Configuration Fields

• name: Host identifier for display purposes
• host: IP address or hostname
• port: Modbus TCP port (default: 502)
• unit_id: Modbus unit ID/slave ID (default: 1)
• timeout: Connection timeout (e.g., "5s", "10s")
• interval: Polling interval (e.g., "1s", "500ms")
• enabled: Whether to poll this host
• registers: Array of registers to poll for this host

Register Configuration Fields

• name: Human-readable name for the register
• address: Modbus address (e.g., 10001 for coil 1)
• type: One of coil, discrete_input, input_register, or holding_register
• min_value: Minimum expected value (optional, for validation)
• max_value: Maximum expected value (optional, for validation)

Output

The client displays results grouped by host:

=== Polling Results ===
Timestamp: 2024-05-05 14:30:00.000
---------------------------------------------------------------

Host: Main Controller
Register                  | Type            | Value    | Time    | Status
-----------------------------------------------------------------------------
Emergency Stop           | coil            | true     |   45ms  | OK
Humidity                 | input_register  | 65       |   60ms  | OK
Temperature              | input_register  | 25       |   50ms  | OK

Host: Sensor Panel
Register                  | Type            | Value    | Time    | Status
-----------------------------------------------------------------------------
X Axis Velocity          | input_register  | 1        |   78ms  | OK
Y Axis Velocity          | input_register  | 2        |   65ms  | OK
Vibration Intensity      | holding_register| 150      |   90ms  | OUT OF RANGE [0-700]

Host: Power Monitor
Register                  | Type            | Value    | Time    | Status
-----------------------------------------------------------------------------
Voltage                  | input_register  | 220      |  120ms  | OK
Current                  | input_register  | 1        |  110ms  | OK
---------------------------------------------------------------

Advanced Features

Parallel Polling

Each host runs in its own goroutine with independent polling intervals. A fast-polling sensor panel won't slow down a slower power monitor.

Error Handling

The client handles:

• Connection failures (retries automatically)
• Communication timeouts
• Invalid responses
• Network interruptions

Resource Management

• Proper connection cleanup on exit
• Context-based cancellation
• Graceful shutdown handling

Performance Considerations

For optimal performance with many hosts:

• Adjust individual timeouts based on network conditions
• Balance polling intervals to avoid overloading the network
• Use the enabled flag to disable unused hosts
• Consider network bandwidth when setting very fast polling intervals

License

MIT