Calculate NK update file SUM, Xanavi/Clarion 72xx

nksum.py

import argparse

def compute_checksum_and_verify(data: bytes) -> bool:
    data_array = bytearray(data)
    checksum_offset = 0x30
    # Read and temporarily clear the stored checksum for region 0
    original_checksum = int.from_bytes(data_array[checksum_offset:checksum_offset+2], byteorder='little')
    data_array[checksum_offset:checksum_offset+2] = [0, 0]
    
    # Calculate checksum by summing all bytes
    calculated_checksum = sum(data_array) & 0xFFFF  # Ensure 16-bit checksum
    
    data_array[checksum_offset:checksum_offset+2] = original_checksum.to_bytes(2, byteorder='little')
    
    # Print calculated checksum
    print(f"File SUM is 0x{original_checksum:04X}")
    print(f"Calculated SUM is 0x{calculated_checksum:04X}")
    

    return calculated_checksum == original_checksum


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Compute checksums in NK Update files.")
    parser.add_argument("input_file", help="Path to the input NK file")
    args = parser.parse_args()
    file_path = args.input_file
    try:
        with open(file_path, 'rb') as file:
            data = file.read()
        is_valid = compute_checksum_and_verify(data)
        print(f"Checksum {'valid' if is_valid else 'invalid'}")
    except FileNotFoundError:
        print(f"Error: File '{file_path}' not found")
    except Exception as e:
        print(f"Error reading file: {e}")