Models flowcharts

  Our two models 

First model 

For the first model: Raspberry Pi communicates with ESP32 with UART we use small protocol to ensure that the data is valid,

 Steps of Communication:

1. Initialize UART on Both Devices:
   • ESP32: Executes Serial.begin(115200) to configure UART0 (TX0/RX0) at a baud rate of 115200 bits per second (bps).
   • RPi4: Configures its UART interface (e.g., using pyserial in Python) to match the 115200 baud rate.
   • Hardware Setup: Connect ESP32’s TX pin to RPi4’s RX pin and ESP32’s RX pin to RPi4’s TX pin via GPIO pins. Ground pins are connected to ensure a common reference.
   • Purpose: Establishes a serial communication channel for bidirectional data transfer.
2. ESP32 Requests Data:
   • The ESP32 initiates communication by sending a single request byte, 0xAA, using Serial.write(0xAA).
   • A 100ms delay (delay(100)) is introduced to allow the RPi4 sufficient time to prepare and send the response.
   • Purpose: Signals the RPi4 to transmit sensor data (e.g., distances and flags).
3. RPi4 Sends Data Frame:
   • The RPi4 responds with an 8-byte frame containing:
     • Byte 1: Header (0xBB) to mark the start of a valid frame.
     • Bytes 2–5: Four distance values (e.g., from ultrasonic sensors).
     • Bytes 6–7: Two flag bytes (e.g., status indicators for safety features).
     • Byte 8: CRC byte for error checking.
   • Frame Format: [0xBB | Dist1 | Dist2 | Dist3 | Dist4 | Flag1 | Flag2 | CRC].
   • Purpose: Delivers structured sensor data to the ESP32.
4. ESP32 Checks for Data Availability:
   • The ESP32 checks if at least 8 bytes are available in the serial buffer using Serial.available() >= 8.
   • If fewer than 8 bytes are present, the function returns false, indicating no valid data.
   • Purpose: Ensures the complete frame is received before processing.
5. Validate Header:
   • The ESP32 reads the first byte using Serial.read() and verifies it equals 0xBB.
   • If the header is invalid (not 0xBB), the ESP32 skips further processing and returns false.
   • Purpose: Confirms the frame is correctly formatted and from the expected source.
6. Read Sensor Data and Flags:
   • The ESP32 reads the next 4 bytes into the distances[] array (representing distance measurements).
   • Reads the following 2 bytes into the flags[] array (representing status or control flags).
   • Purpose: Extracts the payload data for use in safety algorithms (e.g., FCW, BSW).
7. Verify CRC:
   • The ESP32 reads the 8th byte as the received CRC.
   • Calculates the expected CRC by XORing the 6 payload bytes: distances[0] ^ distances[1] ^ distances[2] ^ distances[3] ^ flags[0] ^ flags[1].
   • Compares the received CRC with the expected CRC.
   • Purpose: Detects transmission errors to ensure data integrity.
8. Send Acknowledgment or Rejection:
   • If CRC Matches: The ESP32 sends 0xCC (ACK) using Serial.write(0xCC) and returns true, indicating successful data reception.
   • If CRC Fails: Sends 0xDD (rejection) using Serial.write(0xDD), displays an error message on the LCD (e.g., "Data Error! Re-requesting..."), and returns false.
   • Purpose: Provides feedback to the RPi4, enabling retransmission if needed.

 

Second model