Dual-Controller Synchronization Guide

When to Use This Skill

Apply this skill when the user:

• Has issues with I2C communication between main and camera controllers
• Needs to debug the dual-ESP32 robocar architecture
• Wants to monitor both controllers simultaneously
• Experiences timing or synchronization issues

Architecture Overview

┌─────────────────────┐     I2C      ┌─────────────────────┐
│   Main Controller   │◄────────────►│   Camera Module     │
│  Heltec WiFi LoRa   │              │     ESP32-CAM       │
│                     │              │                     │
│  - AI decisions     │              │  - Image capture    │
│  - Motor control    │              │  - Vision analysis  │
│  - LoRa comms       │              │  - I2C slave        │
└─────────────────────┘              └─────────────────────┘

Build Both Controllers

# Build main controller
make robocar-build-main

# Build camera module
make robocar-build-cam

# Or build both
make robocar-build-all

Monitor Both Controllers

Two Terminal Setup

Open two terminals and monitor both:

Terminal 1 - Main Controller:

make robocar-monitor-main PORT=/dev/cu.usbserial-0001

Terminal 2 - Camera Module:

make robocar-monitor-cam PORT=/dev/cu.usbserial-0002

Identifying Ports

If unsure which device is which:

ls -la /dev/cu.usbserial-* /dev/ttyUSB*

Look for:

• Device that appears first after connecting main controller
• Device that appears after connecting camera module

I2C Communication Debugging

Common I2C Issues

Symptom	Possible Cause	Solution
No response	Wrong address	Verify 7-bit address format
Timeout	Missing pull-ups	Add 4.7K resistors on SDA/SCL
Corrupted data	Speed too fast	Reduce I2C clock frequency
Intermittent	Loose connection	Check wiring

I2C Address Configuration

Ensure both controllers use the same address:

Main controller (master):

#define CAMERA_I2C_ADDR 0x55  // 7-bit address

Camera module (slave):

#define I2C_SLAVE_ADDR 0x55   // Must match master

Verify I2C Wiring

Main Controller          Camera Module
    SDA (21) ◄──────────► SDA (GPIO)
    SCL (22) ◄──────────► SCL (GPIO)
    GND      ◄──────────► GND

Pull-up resistors (4.7K) on SDA and SCL to 3.3V.

Protocol Debugging

Expected Communication Pattern

1. Main sends command byte
2. Camera processes command
3. Camera sends response
4. Main reads response

Debug Logging

Enable verbose I2C logging in both projects:

esp_log_level_set("i2c", ESP_LOG_DEBUG);

Look for matching transactions:

• Main: "Sent command 0x01 to 0x55"
• Camera: "Received command 0x01"

Timing Issues

If commands arrive too fast:

Add delay between commands:

i2c_master_cmd_begin(I2C_NUM, cmd, pdMS_TO_TICKS(100));
vTaskDelay(pdMS_TO_TICKS(10));  // Wait for slave to process

Flash Workflow

Flash Both Controllers

# Flash main controller first
make robocar-flash-main PORT=/dev/cu.usbserial-0001

# Then flash camera (requires GPIO0 to GND)
# Connect GPIO0 to GND on ESP32-CAM
make robocar-flash-cam PORT=/dev/cu.usbserial-0002
# Disconnect GPIO0 from GND and reset

Development Cycle

For rapid iteration:

1. Make code changes
2. Build: make robocar-build-all
3. Flash main: make robocar-flash-main
4. Flash camera (GPIO0→GND): make robocar-flash-cam
5. Monitor both in separate terminals

Common Synchronization Issues

Issue: Camera Not Responding

Symptoms:

• Main reports I2C timeout
• Camera not in monitor output

Debug Steps:

1. Verify camera is powered and running
2. Check I2C address matches
3. Verify GPIO pins for I2C slave
4. Check clock speed compatibility

Issue: Corrupted Data

Symptoms:

• Data received but values wrong
• Checksum failures

Debug Steps:

1. Reduce I2C speed (try 100kHz)
2. Add pull-up resistors
3. Check for noise on long wires
4. Verify endianness of multi-byte data

Issue: Timing Mismatch

Symptoms:

• Works sometimes, fails other times
• Camera not ready when main sends command

Debug Steps:

1. Add handshake mechanism
2. Increase timeout values
3. Use interrupt-based I2C on camera
4. Add ready signal GPIO

Tools and Commands

# Show system info
make robocar-info

# Check environment
make check-environment

# Clean and rebuild
make robocar-clean
make robocar-build-all

# Full dev cycle for main
make robocar-develop-main PORT=/dev/xxx

# Full dev cycle for camera
make robocar-develop-cam PORT=/dev/xxx