#!/usr/bin/env python3
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"""
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CRC16-CCITT Calculator
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Based on the provided C implementation
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"""
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def calculate_crc16(data):
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"""
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Calculate CRC16-CCITT
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Args:
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data: bytes or bytearray
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Returns:
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uint16 CRC value
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"""
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crc = 0xFFFF
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polynomial = 0x1021
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for byte in data:
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crc ^= (byte << 8)
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for _ in range(8):
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if crc & 0x8000:
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crc = (crc << 1) ^ polynomial
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else:
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crc <<= 1
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crc &= 0xFFFF # Keep it 16-bit
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return crc & 0xFFFF
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def main():
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print("=" * 60)
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print("CRC16-CCITT Calculator")
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print("=" * 60)
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print("Enter hex string (space-separated or continuous)")
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print("Example: AA 55 03 09 00 67 00 00 0A 00 00")
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print("Or: AA5503090067000000A0000")
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print("Enter 'q' to quit")
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print("=" * 60)
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while True:
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user_input = input("\nHex data: ").strip()
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if user_input.lower() == 'q':
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print("Goodbye!")
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break
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if not user_input:
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continue
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try:
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# Remove spaces and convert to bytes
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hex_string = user_input.replace(" ", "").replace("0x", "")
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# Validate hex string length (must be even)
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if len(hex_string) % 2 != 0:
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print(f"Error: Hex string length must be even (got {len(hex_string)})")
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continue
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# Convert to bytes
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data = bytes.fromhex(hex_string)
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# Calculate CRC
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crc = calculate_crc16(data)
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# Display results
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print(f"\nInput data ({len(data)} bytes):")
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print(" ".join(f"{b:02X}" for b in data))
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print(f"\nCRC16 Result:")
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print(f" Hex: 0x{crc:04X}")
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print(f" Dec: {crc}")
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print(f" Bytes (Big Endian): {crc >> 8:02X} {crc & 0xFF:02X}")
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print(f" Bytes (Little Endian): {crc & 0xFF:02X} {crc >> 8:02X}")
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except ValueError as e:
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print(f"Error: Invalid hex string - {e}")
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except Exception as e:
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print(f"Error: {e}")
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def test_examples():
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"""Test with known examples from the log"""
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print("\n" + "=" * 60)
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print("Testing with examples from log:")
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print("=" * 60)
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examples = [
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# Frame 1: Speed 10
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("AA 55 03 09 00 67 00 00 0A 00 00", "9E3C", "Full frame (11 bytes)"),
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("09 00 67 00 00 0A 00 00", None, "From DataLen (8 bytes)"),
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("67 00 00 0A 00 00", None, "From SeqNum (6 bytes)"),
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# User's original example from protocol doc
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("AA 55 03 09 00 01 00 00 32 00 00", "C37B", "User example (11 bytes)"),
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]
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for hex_data, expected_crc, description in examples:
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data = bytes.fromhex(hex_data.replace(" ", ""))
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crc = calculate_crc16(data)
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print(f"\n{description}:")
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print(f" Data: {hex_data}")
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print(f" Calculated CRC: 0x{crc:04X}")
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if expected_crc:
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print(f" Expected CRC: 0x{expected_crc}")
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match = (crc == int(expected_crc, 16))
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print(f" Match: {'✓ YES' if match else '✗ NO'}")
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if __name__ == "__main__":
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# Run tests first
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test_examples()
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# Then start interactive mode
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print("\n")
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main()
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