135 lines
3.6 KiB
Python
Executable File
135 lines
3.6 KiB
Python
Executable File
#!/usr/bin/env python2
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# Encodes STM32 firmwares to be flashable from SD card by Chitu motherboards.
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# Relocate firmware to 0x08008800!
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# Copied from Marlin and modified.
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# Licensed under GPL-3.0
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import os
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import random
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import struct
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import uuid
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import sys
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def calculate_crc(contents, seed):
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accumulating_xor_value = seed;
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for i in range(0, len(contents), 4):
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value = struct.unpack('<I', contents[ i : i + 4])[0]
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accumulating_xor_value = accumulating_xor_value ^ value
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return accumulating_xor_value
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def xor_block(r0, r1, block_number, block_size, file_key):
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# This is the loop counter
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loop_counter = 0x0
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# This is the key length
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key_length = 0x18
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# This is an initial seed
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xor_seed = 0x4bad
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# This is the block counter
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block_number = xor_seed * block_number
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#load the xor key from the file
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r7 = file_key
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for loop_counter in range(0, block_size):
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# meant to make sure different bits of the key are used.
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xor_seed = int(loop_counter/key_length)
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# IP is a scratch register / R12
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ip = loop_counter - (key_length * xor_seed)
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# xor_seed = (loop_counter * loop_counter) + block_number
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xor_seed = (loop_counter * loop_counter) + block_number
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# shift the xor_seed left by the bits in IP.
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xor_seed = xor_seed >> ip
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# load a byte into IP
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ip = r0[loop_counter]
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# XOR the seed with r7
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xor_seed = xor_seed ^ r7
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# and then with IP
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xor_seed = xor_seed ^ ip
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#Now store the byte back
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r1[loop_counter] = xor_seed & 0xFF
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#increment the loop_counter
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loop_counter = loop_counter + 1
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def encode_file(input, output_file, file_length):
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input_file = bytearray(input.read())
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block_size = 0x800
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key_length = 0x18
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uid_value = uuid.uuid4()
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file_key = int(uid_value.hex[0:8], 16)
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xor_crc = 0xef3d4323;
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# the input file is exepcted to be in chunks of 0x800
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# so round the size
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while len(input_file) % block_size != 0:
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input_file.extend(b'0x0')
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# write the file header
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output_file.write(struct.pack(">I", 0x443D2D3F))
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# encode the contents using a known file header key
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# write the file_key
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output_file.write(struct.pack("<I", file_key))
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#TODO - how to enforce that the firmware aligns to block boundaries?
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block_count = int(len(input_file) / block_size)
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print("Block Count is ", block_count)
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for block_number in range(0, block_count):
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block_offset = (block_number * block_size)
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block_end = block_offset + block_size
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block_array = bytearray(input_file[block_offset: block_end])
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xor_block(block_array, block_array, block_number, block_size, file_key)
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for n in range (0, block_size):
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input_file[block_offset + n] = block_array[n]
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# update the expected CRC value.
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xor_crc = calculate_crc(block_array, xor_crc)
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# write CRC
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output_file.write(struct.pack("<I", xor_crc))
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# finally, append the encoded results.
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output_file.write(input_file)
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return
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def main():
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if len(sys.argv) != 3:
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print("Usage: update_chitu <input_file> <output_file>")
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exit(1)
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fw, output = sys.argv[1:]
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if not os.path.isfile(fw):
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print("Usage: update_chitu <input_file> <output_file>")
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print("Firmware file", fw, "does not exist")
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exit(1)
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firmware = open(fw, "rb")
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update = open(output, "wb")
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length = os.path.getsize(fw)
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encode_file(firmware, update, length)
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firmware.close()
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update.close()
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print("Encoding complete.")
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if __name__ == '__main__':
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main()
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