diff --git a/lpc-fw-crc.rb b/lpc-fw-crc.rb
new file mode 100755
index 0000000..f6bf754
--- /dev/null
+++ b/lpc-fw-crc.rb
@@ -0,0 +1,72 @@
+#!/usr/bin/env ruby
+# encoding: utf-8
+# ruby: 1.9.3
+=begin
+this script verifies and writes the checksum for NXP LPC13xx firmwares.
+for more information about how it is calculated refer to document UM10375 section 21.7 Criterion for Valid User Code
+=end
+
+def help
+  puts "usage: #{__FILE__} [operation] file"
+  puts "operations:"
+  puts "\t-v,--verify\tverify checksum (default)"
+  puts "\t-w,--write\twrite checksum"
+  puts "file: LPC13xx firmware"
+end
+
+puts "LPC13xx firmware checksum verifier and writer"
+
+# should the checksum be written
+write = false
+file = nil
+
+if ARGV.size==1 then
+  file = ARGV[0]
+elsif ARGV.size==2 then
+  case ARGV[0]
+  when "-h","--help"
+    help
+    exit 0
+  when "-v","--verify"
+    # this is done per default
+  when "-w","--write"
+    write = true
+  else
+    help
+    exit 0
+  end
+  file = ARGV[1]
+else
+  help
+  exit 0
+end
+
+raise "#{file} is not a file" unless File.file? file
+raise "#{file} is too short" if File.size(file)<4*8
+
+firmware = File.open(file,"r+") # open file
+header = firmware.read(4*7).unpack("l*") # read the 7 first words (of 32 bits) to checksum
+checksum = firmware.read(4).unpack("l*")[0]&0xffffffff # read the current checksum (8th word)
+
+# calculate the correct checksum
+sum = 0
+header.each do |word|
+  sum += word
+  sum &= 0xffffffff
+end
+correct = ((~sum)+1)&0xffffffff # the 2's complement
+
+puts "current checksum: 0x%08x" % checksum
+puts "correct checksum: 0x%08x" % correct
+if checksum==correct then
+  puts "checksum matches"
+else
+  puts "checksum does not match"
+  if write then
+    firmware.seek(4*7,:SET)
+    firmware.write([correct].pack("l"))
+    puts "checksum written"
+  end
+end
+firmware.close
+