HTTP-Ethernet-Assistant

HTTP-Ethernet Assistant

Network-controlled hardware assistant that parses JSON commands to execute real-time tasks.

Unique Approach: Implemented twice—first using industry-standard HAL for rapid prototyping, then rewritten in pure bare-metal C to master low-level driver architecture.

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🆚 Dual-Implementation Strategy

I maintain two active branches to demonstrate the difference between “Application Development” and “System Engineering.”

The Bare-Metal Engine (Dev Branch)

“The Deep Dive”

• Philosophy: Zero abstraction. Direct register access.
• Why: To understand exactly how ENC28J60 SPI protocol and LwIP stack interact without HAL overhead.
• Key Tech: Manual SPI driver, custom interrupt handlers, register-level GPIO, LwIP (NO_SYS).
• Status: Active development
• 👉 View Bare-Metal Code

The HAL Reference (Main Branch)

“The Prototype”

• Philosophy: Rapid development using STM32CubeHAL.
• Why: Validated hardware connections, network logic, and ThingSpeak API integration before optimizing.
• Key Tech: STM32 HAL, CubeMX configuration.
• Status: Stable reference implementation
• 👉 View Reference Code

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🏗️ System Architecture

• Hardware Layer: ENC28J60 Ethernet controller (SPI interface) connected to STM32G071RB
• Network Layer: LwIP TCP/IP stack configured in NO_SYS mode (event loop callback style)
• Application Layer: Custom HTTP 1.1 server + JSON command parser
• Cloud Layer: Integration with ThingSpeak for sensor data logging

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🛠️ Tools & Debugging

Development relied heavily on network analysis tools to validate the custom stack:

• Wireshark: Capture raw Ethernet frames, verify TCP 3-way handshake, debug ARP/DHCP sequences
• Packet Sender: Critical for “Echo Testing”—send raw TCP packets to verify stack receives, processes, and returns data without crashing before attempting complex HTTP parsing
• MobaXterm (Serial Monitor): Primary debug console for real-time LwIP assertions, IP address assignment logs, and system status via UART (115200 baud)

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🔌 Hardware Connections

Pinout matches NUCLEO-G071RB configuration

ENC28J60 Signal	STM32 Pin	Arduino Header	Function
SCK	PA1	A1	SPI Clock
MISO	PA6	D12	SPI Master In Slave Out
MOSI	PA7	D11	SPI Master Out Slave In
CS	PA5	D13	Chip Select
INT	PB0	D3	Interrupt (Optional)
RESET	PB1	-	Hardware Reset
VCC	5V	5V	Power
GND	GND	GND	Ground

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🚀 Roadmap

This project is evolving from a simple network endpoint to a fully functional IoT assistant.

Phase 1: Basic Infrastructure (Current Focus)

• ThingSpeak Integration: Implementing REST API client to upload sensor data to cloud—establishes basic “uplink” capability
• Stability: Stress-testing LwIP stack to handle continuous data transmission without memory leaks

Phase 2: Smart Assistant Logic (Next Steps)

• Google Calendar API: Device connects to Google Calendar REST API to fetch daily schedules
• Advanced JSON Parsing: Parse complex nested JSON responses from Google to extract event times and summaries
• Hardware Alarms: Trigger physical alerts (buzzer/LED) based on fetched calendar events

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🧪 Testing the System

1. Monitor Serial Debug (MobaXterm)

1. Open MobaXterm
2. Click Session → Serial
3. Select the STM32 COM Port
4. Set baud rate to 115200
5. Result: You should see IP Assigned: 192.168.0.200 (or similar) in logs

2. Verify Network Connectivity

# Ping the device from your PC terminal
ping 192.168.0.200

3. TCP Echo Test (Packet Sender)

Before trying HTTP, validate the stack using raw TCP Echo test.

• Tool: Packet Sender
• Address: 192.168.0.200
• Port: 7 (Echo Protocol)
• Message: Hello STM32
• Click: Send
• Expected Result: Device receives packet and immediately sends back Hello STM32

4. Control via Web Browser

Once Echo test passes, use the HTTP server.

1. Open web browser (Chrome/Edge/Firefox)
2. Type the IP address: http://192.168.0.200
3. Result: You will see custom control page hosted by STM32
4. Action: Click “Toggle LED” button to control hardware in real-time

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⚔️ The Hard Parts

LwIP in NO_SYS Mode: Integrating full TCP/IP stack without RTOS meant manually managing sys_check_timeouts() loop. Had to ensure Ethernet interrupts didn’t corrupt main loop’s packet processing.

The SPI Bottleneck: ENC28J60 is an SPI device, not memory-mapped. Optimized SPI driver to handle 10Mbps traffic without stalling CPU.

Parsing JSON in C: Standard libraries too heavy. Implemented token-based parser (JSMN style) to read { "cmd": "led", "val": 1 } directly from TCP buffer without malloc.

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Built by Sri Hari Shankar Sharma. Part of the transition from Automotive Applications to Embedded Systems Engineering.