The MGL V6R and V10, ATC VHF radios have a binary protocol (described in the V10 manual), in addition to the ubiquitous Garmin SL40 protocol.
The Emergency/Setup channel is 121.5 MHz. Don't use it for testing...
In this example, I used the Bash
let operator to do the calculations and
printf is treated as a built-in function - TIMTOWTDI.
Frequency
Here is a simple Bash script that computes the frequency message (It doesn't check for out of range values!):
#! /bin/bash
echo MGL V6R ATC VHF Radio Protocol
echo
STX="02" # Message header
DLE="05" # Message header
CC="00" # Active Frequency message ID = 00H, Standby Frequency message ID = 01H
KHZ="000000" # Frequency in Kilohertz, decimal string (6 digits)
KHZH="000000" # Frequency in Kilohertz, hexadecimal string (3 bytes)
KHZ0="00" # Frequency in Kilohertz, B0, LSB first
KHZ1="00" # Frequency in Kilohertz, B1
KHZ2="00" # Frequency in Kilohertz, B2, MSB last
SUM="00" # XOR checksum from CC to last data byte, then XOR with 55H to invert some bits
if [ -n "$1" ]; then
KHZ=$1
echo "Frequency = $KHZ kHz Decimal"
echo
echo "Set serial port USB0 to 9600N81"
stty -F /dev/ttyUSB0 raw
stty -F /dev/ttyUSB0 9600
echo
echo "Compute frequency in hexadecimal"
printf -v KHZH "%06x" "$KHZ"
echo "Frequency MSB first = $KHZH Hex"
KHZ0=$(echo "$KHZH" | cut -c 5-6)
KHZ1=$(echo "$KHZH" | cut -c 3-4)
KHZ2=$(echo "$KHZH" | cut -c 1-2)
echo "Frequency LSB first = $KHZ0$KHZ1$KHZ2 Hex"
echo
# Bash by default handles numbers as decimal ASCII strings.
# A number starting with a zero is considered to be octal.
# A number starting with 0x is considered to be hexadecimal.
# The final modulo 256 reduces the answer to one byte
# and the printf makes it hexadecimal.
echo "Compute byte wide XOR checksum"
let "SUM=0x$CC ^ 0x$KHZ0 ^ 0x$KHZ1 ^ 0x$KHZ2"
let "SUM ^= 0x55"
let "SUM %= 256"
printf -v SUM "%02x" "$SUM"
echo "SUM = $SUM"
echo
# The format string "\x" tells echo to output each variable as an
# 8 bit binary value to the serial port,
# and not as two ASCII characters.
echo "Frequency message = $STX $DLE $CC $KHZ0 $KHZ1 $KHZ2 $SUM"
echo -en "\x$STX\x$DLE\x$CC\x$KHZ0\x$KHZ1\x$KHZ2\x$SUM" > /dev/ttyUSB0
echo
echo "La Voila!"
exit 1
fi
echo Example Emergency Frequency: f 121500
exit 0
I fixed a formatting bug in the checksum routine - these should work OK now.
Volume
Here are two more scripts to change the volume:
#! /bin/bash
# V6R Volume Down
echo MGL V6R ATC VHF Radio Protocol
echo
STX="02" # Message header
DLE="05" # Message header
CC="03" # Volume DOWN message ID = 03H
D0="00" # Unused
SUM="00" # XOR checksum from CC to last data byte, then XOR with 55H to invert some bits
echo "Set serial port USB0 to 9600N81"
stty -F /dev/ttyUSB0 raw
stty -F /dev/ttyUSB0 9600
echo
# Bash by default handles numbers as decimal ASCII strings.
# A number starting with a zero is considered to be octal.
# A number starting with 0x is considered to be hexadecimal.
# The final modulo 256 reduces the answer to one byte
# and the printf makes it hexadecimal.
echo "Compute byte wide XOR checksum"
let "SUM=0x$CC ^ 0x$D0"
let "SUM ^= 0x55"
let "SUM %= 256"
printf -v SUM "%02x" "$SUM"
echo "SUM = $SUM"
echo
# The format string "\x" tells echo to output each variable as an
# 8 bit binary value to the serial port,
# and not as two ASCII characters.
echo "Volume Up message = $STX $DLE $CC $D0 $SUM"
echo -en "\x$STX\x$DLE\x$CC\x$D0\x$SUM" > /dev/ttyUSB0
echo
echo "La Voila!"
exit 1
and the other way:
#! /bin/bash
# V6R Volume Up
echo MGL V6R ATC VHF Radio Protocol
echo
STX="02" # Message header
DLE="05" # Message header
CC="02" # Volume UP message ID = 02H
D0="00" # Unused
SUM="00" # XOR checksum from CC to last data byte, then XOR with 55H to invert some bits
echo "Set serial port USB0 to 9600N81"
stty -F /dev/ttyUSB0 raw
stty -F /dev/ttyUSB0 9600
echo
# Bash by default handles numbers as decimal ASCII strings.
# A number starting with a zero is considered to be octal.
# A number starting with 0x is considered to be hexadecimal.
# The final modulo 256 reduces the answer to one byte
# and the printf makes it hexadecimal.
echo "Compute byte wide XOR checksum"
let "SUM=0x$CC ^ 0x$D0"
let "SUM ^= 0x55"
let "SUM %= 256"
printf -v SUM "%02x" "$SUM"
echo "SUM = $SUM"
echo
# The format string "\x" tells echo to output each variable as an
# 8 bit binary value to the serial port,
# and not as two ASCII characters.
echo "Volume Down message = $STX $DLE $CC $D0 $SUM"
echo -en "\x$STX\x$DLE\x$CC\x$D0\x$SUM" > /dev/ttyUSB0
echo
echo "La Voila!"
exit 1
By implementing this in a Bash script, any problems can be fixed easily and one will probably only need to rearrange some variables in the final echo statements to make it work.
Zenity Press To Talk
Here is a more advanced script that uses Zenity to pretty things up and key the radio PTT over the serial port. Note that if the radio 'hits you with a flat ignore', then you need to upgrade the firmware, since there is an old version around that has a PTT protocol bug:
#! /bin/bash
echo VHF PTT Script
echo Depends on: zenity, stty
echo "Set serial port USB0 to 9600N81"
stty -F /dev/ttyUSB0 raw
stty -F /dev/ttyUSB0 9600
sleep 1
# Message Protocol
# Repeat PTT message every 100 ms, timeout after 500 ms
STX="02" # Message header
DLE="05" # Message header
CC="0B" # PTT message ID = 0BH
PTT="01" # OFF=00H, ON=01H, default to ON
SUM="00" # XOR checksum from CC to last data byte, then XOR with 55H to invert some bits
# Bash by default handles numbers as decimal ASCII strings.
# A number starting with a zero is considered to be octal.
# A number starting with 0x is considered to be hexadecimal.
# The final modulo 256 reduces the answer to one byte
# and the printf makes it hexadecimal.
let "SUM=0x$CC ^ 0x$PTT"
let "SUM ^= 0x55"
let "SUM %= 256"
printf -v SUM "%02x" "$SUM"
echo "SUM = $SUM"
echo "PTT message = $STX $DLE $CC $PTT $SUM"
# See the Zenity progress manual for details:
# https://help.gnome.org/users/zenity/stable/progress.html.en
PTT=0
(
while true; do
echo $PTT
echo "# PTT ON..."
sleep 0.1
let "PTT=$PTT+10"
if [ "$PTT" -eq "100" ]; then
PTT=0
fi
# Repeatedly send PTT ON message
# The format string "\x" tells echo to output each variable as an
# 8 bit binary value to the serial port,
# and not as two ASCII characters.
echo -en "\x$STX\x$DLE\x$CC\x$PTT\x$SUM" > /dev/ttyUSB0
done
) |
zenity --progress \
--title="VHF Radio" \
--text="PTT ON" \
--percentage=0
# Wait a little bit to avoid clipping the end of the transmission
sleep 0.2
echo "PTT OFF"
PTT=0
let "SUM=0x$CC ^ 0x$PTT"
let "SUM ^= 0x55"
let "SUM %= 256"
printf -v SUM "%02x" "$SUM"
echo "SUM = $SUM"
echo "PTT message = $STX $DLE $CC $PTT $SUM"
echo -en "\x$STX\x$DLE\x$CC\x$PTT\x$SUM" > /dev/ttyUSB0
# Wait for the dust to settle
sleep 0.1
exit 0
Zenity Frequency
This is a prettied script to set the frequency using Zenity sliders:
#! /bin/bash
echo VHF Frequency Script
echo Version: 0.1, 16 Sep 2015
echo Depends on: zenity, stty
zenity --question \
--title="VHF Radio" \
--text="Set VHF Radio Frequency?" \
--ok-label="OK" \
--cancel-label="Cancel"
if [ $? -eq 1 ]; then
echo Cancel
exit
fi
echo OK
# VHF frequency range: 118.000 to 136.975 MHz
MM=$( zenity --scale \
--title "VHF Radio" \
--text "Frequency 1XX MHz" \
--min-value=18 \
--max-value=36 \
--value=10 )
KK=$( zenity --scale \
--title "VHF Radio" \
--text "Frequency XX0 kHz" \
--min-value=0 \
--max-value=99 \
--value=10 )
K=$( zenity --scale \
--title "VHF Radio" \
--text "Frequency 00X kHz" \
--min-value=0 \
--max-value=9 \
--value=0 )
# Raw unvalidated frequency
echo Unvalidated Frequency = "1""$MM""$KK""$K"
# Valid frequencies must be divisible by 25 kHz
MMM="1""$MM"
KKK="$KK""$K"
echo MHz=$MMM
echo kHz=$KKK
let "MOD=$KKK % 25"
echo MOD=$MOD
let "KKK=$KKK - $MOD"
echo "Validated Frequency = "$MMM"".""$KKK" MHz"
echo Start a progress dialogue
zenity --progress \
--width=350 \
--title="VHF Radio" \
--text="Set VHF Radio Frequency... " \
--pulsate &
PID=$!
echo MGL V6R ATC VHF Radio Protocol
echo
STX="02" # Message header
DLE="05" # Message header
CC="00" # Active Frequency message ID = 00H, Standby Frequency message ID = 01H
KHZ="000000" # Frequency in Kilohertz, decimal string (6 digits)
KHZH="000000" # Frequency in Kilohertz, hexadecimal string (3 bytes)
KHZ0="00" # Frequency in Kilohertz, B0, LSB first
KHZ1="00" # Frequency in Kilohertz, B1
KHZ2="00" # Frequency in Kilohertz, B2, MSB last
SUM="00" # XOR checksum from CC to last data byte, then XOR with 55H to invert some bits
# Decimal frequency
KHZ="$MMM""$KKK"
echo "Frequency = $KHZ kHz Decimal"
echo
echo "Set serial port USB0 to 9600N81"
stty -F /dev/ttyUSB0 raw
stty -F /dev/ttyUSB0 9600
# Wait for the dust to settle
sleep 1
echo "Compute frequency in hexadecimal"
printf -v KHZH "%06x" "$KHZ"
echo "Frequency MSB first = $KHZH Hex"
KHZ0=$(echo "$KHZH" | cut -c 5-6)
KHZ1=$(echo "$KHZH" | cut -c 3-4)
KHZ2=$(echo "$KHZH" | cut -c 1-2)
echo "Frequency LSB first = $KHZ0$KHZ1$KHZ2 Hex"
echo
# Bash by default handles numbers as decimal ASCII strings.
# A number starting with a zero is considered to be octal.
# A number starting with 0x is considered to be hexadecimal.
# The final modulo 256 reduces the answer to one byte
# and the printf makes it hexadecimal.
let "SUM=0x$CC ^ 0x$KHZ0 ^ 0x$KHZ1 ^ 0x$KHZ2"
let "SUM ^= 0x55"
let "SUM %= 256"
printf -v SUM "%02x" "$SUM"
echo "SUM = $SUM"
echo
# The format string "\x" tells echo to output each variable as an
# 8 bit binary value to the serial port,
# and not as two ASCII characters.
echo "Frequency message = $STX $DLE $CC $KHZ0 $KHZ1 $KHZ2 $SUM"
echo -en "\x$STX\x$DLE\x$CC\x$KHZ0\x$KHZ1\x$KHZ2\x$SUM" > /dev/ttyUSB0
# Wait for the dust to settle
sleep 1
echo Kill the progress dialogue
kill $PID
zenity --info \
--title "VHF Radio" \
--text "Frequency = "$MMM"".""$KKK" MHz" \
-- no-wrap
echo Done!
Use at your own peril though...
Interactive Scripts with 'chat'
A typical exchange with a radio or other embedded device goes something like:
- Send a command
- Get a response
- If the response was good, then do an action
- If the response was bad, then quit
Automating that with
echo,
cat and
if statements is difficult. The
chat program is part of the
pppd package and is probably installed by default. You could use
chat to do scripts more effectively than with standard
bash commands.
http://www.tldp.org/HOWTO/PPP-HOWTO/x1219.html
For example, receive ERROR, then abort, receive nothing then send at&v, receive OK then set register 9 to 2, or timeout after 3 seconds:
$ chat -v TIMEOUT 3 ABORT ERROR '' at&v OK ats9=2 </dev/ttyUSB0 >/dev/ttyUSB0
With a few lines like the above in a script, you can do most anything with a simple radio modem device.
Serial Port Redirection
When playing with serial ports in scripts, you will find that each time you open and close the port, it takes time, so it can drop characters and the buffer contents become unknown also.
A simple trick to avoid opening and closing the port with each line of code, is to use the
exec program to do permanent redirection of the
stdio files. After that, any program that reads and writes to
stdio will talk to the serial port. This is perhaps better explained with an example:
DEV="/dev/ttyUSB0"
exec 3<&1 >"$DEV" <"$DEV"
File handle
0 is
stdin, filehandle
1 is
stdout and
2 is
stderror, so
3<&1 means redirect
stdout to a new handle
3 and the
>"$DEV" means simultaneously also redirect it to the USB serial port and lastly,
<"$DEV" means redirect the USB serial port to
stdin.
From then on, your
chat script doesn't have to add
<"$DEV" >"$DEV" to the end of every line and if you need to
echo a message to
stdout, you can use handle
3 also.
More explanations on
exec redirection here:
http://wiki.bash-hackers.org/howto/redirection_tutorial
Serial Port Tips
www.aeronetworks.ca/2015/01/serial-port-io.htmlwww.aeronetworks.ca/2014/10/serial-ports-revisited.htmlwww.aeronetworks.ca/2014/01/crcs-and-serial-ports.htmlwww.aeronetworks.ca/2013/10/serial-port-tricks.htmlwww.aeronetworks.ca/2013/05/usb-serial-device-with-unknown-ids.htmlwww.aeronetworks.ca/2015/10/reading-and-parsing-data-from-serial.htmlwww.aeronetworks.ca/2013/05/compile-moxa-serial-widget-device.html
La voila!
Herman
