#!/bin/sh
#
# ubx packet generator   v0.1  Andy Green <andy@openmoko.com>
#
# Usage:
#
# ubxcs b5 62 06 13 04 00 01 00 00 00 > ubx-packet.bin
#
# appends checksum and issues binary packet on stdout
#
# you can subsequently issue the packet to GPS unit like this
#
# cat ubx-packet.bin > /dev/ttySAC1

cs0=0
cs1=0
seen=0

until [ -z "$1" ]
do
  upr=`echo $1 | tr [[:lower:]] [[:upper:]]`
  dec=`echo "ibase=16;obase=A;$upr" | bc`

  if [ $seen -gt 1 ] ; then

   cs0=$(( $cs0 + $dec ))
   cs0="$(( $cs0 & 255 ))"
   cs1=$(( $cs1 + $cs0 ))
   cs1="$(( $cs1 & 255 ))"

  fi

  echo -e -n "\x$upr"

  shift

  seen=$(( $seen + 1 ))

done

echo -e -n "\x`echo "ibase=10;obase=16;$cs0" | bc`\x`echo "ibase=10;obase=16;$cs1" | bc`"