diff --git a/tools/hexChecksum.pl b/tools/hexChecksum.pl
new file mode 100644
index 0000000..d2fd369
--- /dev/null
+++ b/tools/hexChecksum.pl
@@ -0,0 +1,48 @@
+#!/usr/bin/perl -w
+#      Copyright (C) 2014 Michael McMaster <michael@codesrc.com>
+#
+#      This file is part of SCSI2SD.
+#
+#      SCSI2SD is free software: you can redistribute it and/or modify
+#      it under the terms of the GNU General Public License as published by
+#      the Free Software Foundation, either version 3 of the License, or
+#      (at your option) any later version.
+#
+#      SCSI2SD 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 General Public License for more details.
+#
+#      You should have received a copy of the GNU General Public License
+#      along with SCSI2SD.  If not, see <http://www.gnu.org/licenses/>.
+
+# Calculates the checksum of all flash data within Cypress PSoC 5lp .hex files
+# Allows fixing the checksum after manual hacking of the hex files
+
+use strict;
+use warnings;
+
+my $sum = 0;
+while (my $line = <>)
+{
+
+	$line =~ s/[\n\r]//g;
+
+	if ($line =~ /^:40[0-9A-F]{4}00(.+)[0-9A-F]{2}$/)
+	{
+		my $binrec = pack('H*', $1);
+		$sum += unpack('%16C*', $binrec);
+	}
+	elsif ($line eq ":0200000490303A")
+	{
+		my $checksumRec = sprintf(":02000000%04X",  ($sum & 0xffff));
+
+		# create checksum of checksum record.
+		my $sum2 = unpack('%8C*',  pack('H*', substr($checksumRec, 1)));
+		$checksumRec .= sprintf('%2X', (~$sum2 + 1) & 0xFF);
+		print("Flash data checksum record = $checksumRec\n");
+		print("(Replace line below ':0200000490303A'\n");
+		exit;
+	}
+
+}