Advanced MQTT Pub/Sub Example

MQTT Advanced Pub/Sub Example

Overview

This NetBurner application demonstrates advanced MQTT publish/subscribe functionality with additional features including remote configuration management and GPIO pin control over MQTT. The application serves as a comprehensive example of integrating MQTT communication with embedded system control capabilities.

Features

Core MQTT Functionality

• Automatic Publishing: Publishes "Hello World" messages to testTopic/HelloWorld every 10 seconds
• Message Subscription: Subscribes to the same topic and echoes received messages to the serial console
• Connection Management: Handles MQTT connection establishment and recovery automatically
• Rate Limiting: Implements publish rate limiting (20 messages per 5 seconds, burst of 4)

Advanced Features

• Remote Configuration: Exposes NetBurner Config system via MQTT topic device/nburnxxxxxx/config
• GPIO Control: Allows remote control of device pins through MQTT topics device/nburnxxxxxx/pins/+
• MAC-Based Topics: Uses device MAC address for unique topic identification
• Multi-Platform Support: Supports various NetBurner platforms with different pin configurations

MQTT Topics

Published Topics

• testTopic/HelloWorld - Publishes "Hello World" message every 10 seconds

Subscribed Topics

• testTopic/HelloWorld - Echoes received messages to serial console
• device/nburn_{MAC}/config - Configuration management interface
• device/nburn_{MAC}/pins/+ - GPIO pin control interface

Note

{MAC} is replaced with the last 3 octets of the device's MAC address (e.g., device/nburn123456/config)

GPIO Control

Pin Control Format

The application accepts pin control messages in the following formats:

For platforms with direct pin access (NANO54415, SB800EX, SOMRT1061, SBE70LC):**

• Topic: device/nburn_{MAC}/pins/{pin_number}

• Examples: device/nburn123456/pins/1, device/nburn123456/pins/15

  For platforms with header/pin structure (MOD5441X):**

• Topic: device/nburn_{MAC}/pins/{header}/{pin}
• Examples: device/nburn123456/pins/1/5, device/nburn123456/pins/2/3

Control Values

Pins can be controlled using various message formats:

• 1 or true - Set pin HIGH
• 0 or false - Set pin LOW
  
• Any numeric value - Set pin to that boolean value (0 = LOW, non-zero = HIGH)

Application Flow

1. Initialization
   • Initialize file system (if not present)
   • Initialize network stack
   • Wait for active network connection
   • Configure MQTT client with rate limiting
2. Connection Phase
   • Establish MQTT connection using configured broker settings
   • Wait for connection establishment before proceeding
3. Operation Phase
   • Subscribe to echo topic (testTopic/HelloWorld)
   • Enter main loop:
     • Publish "Hello World" message every 10 seconds
     • Process incoming MQTT messages
     • Handle pin control requests
     • Monitor for user input to change states
4. Message Handling
   • Echo messages: Forward received messages to serial console
   • Pin control: Parse topic and message to control GPIO pins
   • Configuration: Handle remote configuration changes

Configuration

The application uses the NetBurner Config system for MQTT broker configuration:

• Broker URI
• Username/Password authentication
• SSL/TLS certificates (stored in file system)
• Connection parameters

Configuration can be modified remotely via the MQTT configuration topic.

Build Requirements

• NetBurner NNDK (NetBurner Network Development Kit)
• Supported NetBurner hardware platform
• MQTT broker for testing

Usage Instructions

1. Setup
   • Configure MQTT broker settings using NetBurner Config system
   • Flash the application to your NetBurner device
   • Ensure network connectivity
2. Testing
   • Monitor serial output for connection status and published messages
   • Use MQTT client to subscribe to testTopic/HelloWorld to see published messages
   • Publish messages to testTopic/HelloWorld to test echo functionality
   • Control GPIO pins by publishing to appropriate pin control topics
3. Interactive Control
   • Press any key during operation to change application states
   • Use serial console to monitor application status and debug information

Platform-Specific Notes

Supported Platforms

• NANO54415: Direct pin access via Pins[] array
• SB800EX: Direct pin access via Pins[] array
  
• SOMRT1061: Direct pin access via Pins[] array
• SBE70LC: Direct pin access via Pins[] array
• MOD5441X: Header-based pin access (J1/J2 headers)

Pin Control Differences

• Direct access platforms: Use single pin number (e.g., /pins/5)
• Header-based platforms: Use header/pin format (e.g., /pins/1/5 for J1 pin 5)

Error Handling

• Connection Loss: Automatically attempts reconnection
• Subscription Failures: Reports error codes and reason strings
• Invalid Pin Messages: Silently ignores malformed pin control messages
• Rate Limiting: Prevents message flooding with configurable limits

Debug Information

The application provides extensive debug output including:

• Connection status updates
• Subscription confirmation
• Message reception notifications
• Pin control operations
• Error conditions and recovery attempts

Security Considerations

• Uses NetBurner's built-in MQTT security features
• Supports SSL/TLS encryption when configured
• MAC-based topic naming provides device-specific addressing
• Configuration changes logged for audit trail