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Protocol Layer Documentation (src/protocols/)

AI Reasoning: This document explains the AI's reasoning for protocol layer implementations.

⚠️ This is AI-generated content - verify against hardware before use

Overview

The protocol layer handles communication protocols: Bluetooth, GPS, and USB CDC.

Bluetooth Protocol (protocols/bluetooth.c)

Why This Implementation?

AI Reasoning:

  • Bluetooth module connected via UART (USART1, PA9/PA10)
  • 115200 baud rate (observed in Bluetooth_UART1_Init)
  • AT command set (typical for serial Bluetooth modules)

Hardware:

  • TX: PA9 (USART1)
  • RX: PA10 (USART1)
  • Baud: 115200 (confirmed from OEM firmware)

Confidence: HIGH - UART and baud rate confirmed

AI Assumptions:

  • AT command set is guessed (not extracted from OEM firmware)
  • Module type unknown (HC-05, BC417, etc.)
  • Pairing/connection logic guessed

Potential Issues:

  • AT commands may be completely different
  • Connection process may not work
  • Baud rate may need adjustment

GPS Protocol (protocols/gps.c)

Why NMEA Parsing?

AI Reasoning:

  • GPS modules use standard NMEA 0183 format
  • USART3 configured for 9600 baud (observed in OEM firmware)
  • NMEA sentences are public standard (no reverse engineering needed)

NMEA Sentences:

  • $GPRMC: Recommended minimum specific GPS data
  • $GPGGA: Global positioning system fix data
  • $GPGSV: GPS satellite data

Confidence: HIGH - NMEA is standard format, baud rate confirmed

Potential Issues:

  • GPS module may use different baud rate
  • May need different sentence types
  • Parsing may have bugs

USB CDC Protocol (protocols/cdc_protocol.c)

Why Binary Protocol?

AI Reasoning:

  • OEM bootloader uses binary protocol over USB CDC
  • Frame format: 0xAA [cmd] [len] [data...] [crc16] 0x55
  • Captured from USB packet analysis
  • Used for firmware updates and memory access

Protocol Details:

  • Start byte: 0xAA
  • End byte: 0x55
  • CRC-16 XMODEM for validation
  • Commands: 0x42 (binary mode), 0x0A (version), etc.

Confidence: HIGH - Protocol captured from USB analysis

Potential Issues:

  • Some commands may be missing
  • Error handling may be incomplete
  • Signature checks may prevent flashing

Key AI Assumptions

  1. Bluetooth AT Commands: Completely guessed (LOW confidence)
  2. GPS NMEA: Standard format (HIGH confidence)
  3. USB CDC Protocol: Captured from USB analysis (HIGH confidence)

Verification Needed

  • Test Bluetooth AT commands actually work
  • Verify GPS NMEA parsing extracts correct data
  • Test USB CDC protocol with OEM bootloader
  • Verify baud rates are correct
  • Test connection establishment
  • Verify error handling

Data Sources

  1. OEM Firmware: UART initialization functions, baud rates
  2. USB Captures: CDC protocol frame format
  3. Standards: NMEA 0183 (public standard)