trezor-firmware/legacy/bootloader/combine/prepare.py

#!/usr/bin/env python
from __future__ import print_function

bl = open("bl.bin").read()
fw = open("fw.bin").read()
combined = bl + fw[:256] + (32768 - 256) * "\x00" + fw[256:]

open("combined.bin", "w").write(combined)

print("bootloader : %d bytes" % len(bl))
print("firmware   : %d bytes" % len(fw))
print("combined   : %d bytes" % len(combined))