feat: Add Modbus RTU support with multi-drop architecture by thiagoralves · Pull Request #83 · Autonomy-Logic/openplc-runtime

thiagoralves · 2026-01-21T03:49:33Z

Summary

Adds Modbus RTU (serial) communication support alongside existing Modbus TCP functionality
Implements multi-drop architecture allowing multiple devices on the same serial port with different slave IDs
Adds REST endpoint to list available serial ports for the frontend

Changes

1. Serial Ports REST Endpoint (`webserver/app.py`)

New GET /api/serial-ports endpoint
Returns list of available serial ports with device path and description

2. Connection Manager (`modbus_master_connection.py`)

Refactored to support both TCP and RTU transport types
Factory method _create_client() creates appropriate pymodbus client
Added RTU parameters: serial_port, baud_rate, parity, stop_bits, data_bits

3. Config Model (`modbus_master_config_model.py`)

Added TransportType ('tcp' | 'rtu') and ParityType ('N' | 'E' | 'O')
Extended ModbusDeviceConfig with RTU-specific fields
Transport-specific validation rules
Multi-drop validation (prevents duplicate slave IDs on same bus)

4. Plugin Updates (`modbus_master_plugin.py`)

New ModbusRtuBusHandler class for multi-drop RTU support
One thread per serial bus handling multiple slave IDs
group_rtu_devices_by_bus() helper function
Updated start_loop() to separate TCP and RTU device handling

5. Dependencies (`requirements.txt`)

Added pyserial>=3.5

Multi-Drop Architecture

Devices on the same serial port share a single connection
Each device has a unique slave_id (1-247)
All IO operations include the device-specific slave_id
Bus grouping key: serial_port:baud_rate:parity:stop_bits:data_bits

Backward Compatibility

Existing TCP configurations work without changes
Missing transport field defaults to 'tcp'

Test plan

Test existing Modbus TCP devices still work
Test RTU device with single slave ID
Test multi-drop RTU with multiple devices on same serial port
Test serial ports API endpoint returns correct ports
Test connection retry and reconnection logic for RTU

🤖 Generated with Claude Code

This commit adds Modbus RTU (serial) communication support to the modbus master plugin, enabling serial communication with Modbus slave devices alongside existing TCP functionality. Key changes: 1. Serial ports REST endpoint (webserver/app.py): - New GET endpoint at /api/serial-ports - Lists available serial ports using pyserial 2. Connection manager refactoring (modbus_master_connection.py): - Support for both TCP and RTU transport types - Factory method _create_client() for transport-specific clients - RTU parameters: serial_port, baud_rate, parity, stop_bits, data_bits 3. Config model updates (modbus_master_config_model.py): - TransportType and ParityType type literals - RTU-specific fields in ModbusDeviceConfig - Transport-specific validation rules - Multi-drop validation (duplicate slave IDs on same bus) 4. Plugin updates (modbus_master_plugin.py): - New ModbusRtuBusHandler class for multi-drop RTU support - One thread per serial bus, handling multiple slave IDs - group_rtu_devices_by_bus() helper function - Updated start_loop() to separate TCP and RTU device handling 5. Dependencies (requirements.txt): - Added pyserial>=3.5 Multi-drop RTU architecture: - Devices on same serial port share a single connection - Each device has unique slave_id (1-247) - IO operations include slave_id to route to correct device - Bus grouping key: serial_port:baud_rate:parity:stop_bits:data_bits Backward compatibility: - Existing TCP configurations work without changes - Missing transport field defaults to "tcp" Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Copilot

Pull request overview

This PR adds Modbus RTU (serial) communication support alongside the existing Modbus TCP functionality, implementing a multi-drop architecture that allows multiple devices to share a single serial port using unique slave IDs.

Changes:

Adds REST API endpoint to list available serial ports
Extends configuration model to support both TCP and RTU transport types with appropriate validation
Refactors connection manager to create either TCP or RTU clients based on transport type
Implements multi-drop RTU bus handler that manages multiple slave devices on a single serial connection

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
webserver/app.py	Adds `/api/serial-ports` endpoint to list available serial ports for frontend configuration
modbus_master_config_model.py	Extends device config with RTU parameters, transport-specific validation, and multi-drop slave ID conflict detection
requirements.txt	Adds pyserial dependency for serial port communication
modbus_master_plugin.py	Implements RTU bus handler for multi-drop architecture and updates plugin startup to handle both TCP and RTU devices
modbus_master_connection.py	Refactors connection manager to support both TCP and RTU transports with factory method for client creation

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Copilot · 2026-01-21T03:52:35Z

+        all_cycle_times = [p.cycle_time_ms for d in devices for p in d.io_points]
+        self.gcd_cycle_time_ms = calculate_gcd_of_cycle_times(
+            [type('obj', (object,), {'cycle_time_ms': ct})() for ct in all_cycle_times]
+        ) if all_cycle_times else 1000


The creation of anonymous objects using type('obj', (object,), {'cycle_time_ms': ct})() is unnecessarily complex and hard to understand. Consider creating a simple dataclass or named tuple to represent cycle time objects, or refactor calculate_gcd_of_cycle_times to accept a list of integers directly instead of requiring objects with a cycle_time_ms attribute.

Copilot · 2026-01-21T03:52:35Z

+        gcd_cycle_time_seconds = self.gcd_cycle_time_ms / 1000.0
+
+        if not self.all_io_points:
+            self.logger.warn(f"[{self.name}] No I/O points defined. Stopping thread.")


The warn method is deprecated. Use warning instead to follow Python's standard logging best practices.

Suggested change

self.logger.warn(f"[{self.name}] No I/O points defined. Stopping thread.")

self.logger.warning(f"[{self.name}] No I/O points defined. Stopping thread.")

Copilot · 2026-01-21T03:52:35Z

+                                address, count=count, device_id=slave_id
+                            )
+                        else:
+                            self.logger.warn(f"[{self.name}] Unsupported read FC: {point.fc}")


The warn method is deprecated. Use warning instead to follow Python's standard logging best practices.

Suggested change

self.logger.warn(f"[{self.name}] Unsupported read FC: {point.fc}")

self.logger.warning(f"[{self.name}] Unsupported read FC: {point.fc}")

Copilot · 2026-01-21T03:52:36Z

+                                address, values_to_write, device_id=slave_id
+                            )
+                        else:
+                            self.logger.warn(f"[{self.name}] Unsupported write FC: {point.fc}")


The warn method is deprecated. Use warning instead to follow Python's standard logging best practices.

Suggested change

self.logger.warn(f"[{self.name}] Unsupported write FC: {point.fc}")

self.logger.warning(f"[{self.name}] Unsupported write FC: {point.fc}")

The handle_list_serial_ports endpoint in app.py needs pyserial to enumerate available serial ports, but it runs in the main webserver context. Previously pyserial was only installed in the modbus_master plugin's virtual environment. This fix adds pyserial to the main requirements.txt so the serial port listing API endpoint works correctly. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

thiagoralves requested a review from Copilot January 21, 2026 03:51

Copilot AI reviewed Jan 21, 2026

View reviewed changes

thiagoralves merged commit 414bb91 into development Jan 21, 2026
1 check passed

thiagoralves deleted the feature/modbus-rtu-support branch January 21, 2026 23:32

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feat: Add Modbus RTU support with multi-drop architecture#83

feat: Add Modbus RTU support with multi-drop architecture#83
thiagoralves merged 2 commits into
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feature/modbus-rtu-support

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	self.logger.warn(f"[{self.name}] No I/O points defined. Stopping thread.")
	self.logger.warning(f"[{self.name}] No I/O points defined. Stopping thread.")

	self.logger.warn(f"[{self.name}] Unsupported read FC: {point.fc}")
	self.logger.warning(f"[{self.name}] Unsupported read FC: {point.fc}")

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thiagoralves commented Jan 21, 2026

Summary

Changes

1. Serial Ports REST Endpoint (webserver/app.py)

2. Connection Manager (modbus_master_connection.py)

3. Config Model (modbus_master_config_model.py)

4. Plugin Updates (modbus_master_plugin.py)

5. Dependencies (requirements.txt)

Multi-Drop Architecture

Backward Compatibility

Test plan

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Pull request overview

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1. Serial Ports REST Endpoint (`webserver/app.py`)

2. Connection Manager (`modbus_master_connection.py`)

3. Config Model (`modbus_master_config_model.py`)

4. Plugin Updates (`modbus_master_plugin.py`)

5. Dependencies (`requirements.txt`)