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#!/usr/bin/env python3
# Encodes STM32 firmwares to be flashable from SD card by Chitu motherboards.
# Relocate firmware to 0x08008800!
# Copied from Marlin and modified.
# Licensed under GPL-3.0
import os
import struct
import uuid
import sys
import hashlib
def calculate_crc(contents, seed):
accumulating_xor_value = seed;
for i in range(0, len(contents), 4):
value = struct.unpack('<I', contents[ i : i + 4])[0]
accumulating_xor_value = accumulating_xor_value ^ value
return accumulating_xor_value
def xor_block(r0, r1, block_number, block_size, file_key):
# This is the loop counter
loop_counter = 0x0
# This is the key length
key_length = 0x18
# This is an initial seed
xor_seed = 0x4bad
# This is the block counter
block_number = xor_seed * block_number
#load the xor key from the file
r7 = file_key
for loop_counter in range(0, block_size):
# meant to make sure different bits of the key are used.
xor_seed = int(loop_counter/key_length)
# IP is a scratch register / R12
ip = loop_counter - (key_length * xor_seed)
# xor_seed = (loop_counter * loop_counter) + block_number
xor_seed = (loop_counter * loop_counter) + block_number
# shift the xor_seed left by the bits in IP.
xor_seed = xor_seed >> ip
# load a byte into IP
ip = r0[loop_counter]
# XOR the seed with r7
xor_seed = xor_seed ^ r7
# and then with IP
xor_seed = xor_seed ^ ip
#Now store the byte back
r1[loop_counter] = xor_seed & 0xFF
#increment the loop_counter
loop_counter = loop_counter + 1
def encode_file(input, output_file, file_length):
input_file = bytearray(input.read())
block_size = 0x800
key_length = 0x18
file_digest = hashlib.md5(input_file).digest()
uid_value = uuid.UUID(bytes=file_digest)
print("Update UUID ", uid_value)
file_key = int(uid_value.hex[0:8], 16)
xor_crc = 0xef3d4323;
# the input file is expected to be in chunks of 0x800
# so round the size
while len(input_file) % block_size != 0:
input_file.extend(b'0x0')
# write the file header
output_file.write(struct.pack(">I", 0x443D2D3F))
# encode the contents using a known file header key
# write the file_key
output_file.write(struct.pack("<I", file_key))
#TODO - how to enforce that the firmware aligns to block boundaries?
block_count = int(len(input_file) / block_size)
print("Block Count is ", block_count)
for block_number in range(0, block_count):
block_offset = (block_number * block_size)
block_end = block_offset + block_size
block_array = bytearray(input_file[block_offset: block_end])
xor_block(block_array, block_array, block_number, block_size, file_key)
for n in range (0, block_size):
input_file[block_offset + n] = block_array[n]
# update the expected CRC value.
xor_crc = calculate_crc(block_array, xor_crc)
# write CRC
output_file.write(struct.pack("<I", xor_crc))
# finally, append the encoded results.
output_file.write(input_file)
return
def main():
if len(sys.argv) != 3:
print("Usage: update_chitu <input_file> <output_file>")
exit(1)
fw, output = sys.argv[1:]
if not os.path.isfile(fw):
print("Usage: update_chitu <input_file> <output_file>")
print("Firmware file", fw, "does not exist")
exit(1)
firmware = open(fw, "rb")
update = open(output, "wb")
length = os.path.getsize(fw)
encode_file(firmware, update, length)
firmware.close()
update.close()
print("Encoding complete.")
if __name__ == '__main__':
main()
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