#!/usr/bin/python
#
# Compute and insert the vector table checksum required for booting the
# LPC43xx and some other NXP ARM microcontrollers.
#
# usage: lpcvtcksum firmware.bin
#
# Copyright (C) 2012 Michael Ossmann <mike@ossmann.com>
#
# This library is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this library.  If not, see <http://www.gnu.org/licenses/>.

import sys, struct

binfile = open(sys.argv[1], 'r+b')
rawvectors = binfile.read(32)
vectors = list(struct.unpack('<IIIIIIII', rawvectors))

# compute vector table checksum
sum = 0
for i in range(7):
	sum += vectors[i]
vectors[7] = 1 + (0xffffffff ^ (0xffffffff & sum))

print "computed vector table checksum: 0x%08x" % vectors[7]

rawremainder = binfile.read()
remainder = list(struct.unpack('B' * len(rawremainder), rawremainder))
numbytes = len(remainder) + 32

# pad to multiple of 4096 bytes to make GoodFET happy
if (numbytes % 4096):
	remainder.extend([0] * (4096 - numbytes % 4096))

# rewrite file with checksum and padding
data = vectors
data.extend(remainder)
binfile.seek(0)
binfile.write(struct.pack('<IIIIIIII' + 'B' * len(remainder), *data))
