# List all packet types that this script knows about
my %Idents = (
	Rotation_Marker => 0x90,
	Format_7	=> 0x87,
);

# List packet lengths of each of the packet types (Ident char to checksum, inclusive)
my %Packet_Length = (
	$Idents{ Rotation_Marker }	=> 30,
	$Idents{ Format_7 }		=> 28,
);

# unpack templates to use for each packet type (not including the packet Ident)
my %packet_template = (
	$Idents{ Rotation_Marker } => "C3 n n n n n n n n n n n n C3",
	$Idents{ Format_7 }	=> "C B16 n2 A4 A8 A2 A A A3 C2",
);

##</code><code>##

my @packet_fields = qw(	ident
			flags
			x
			y
			mode3
			callsign
			route
			spare1
			spare2
			flight_level
			terminator
			chksum
			);
my @rotation_packet_fields = qw(ident
				RDP_Ident
				Radar_Site_Ident
				site_x
				site_y
				Useful_Vol_Upper
				Useful_Vol_Lower
				Useful_Vol_North
				Useful_Vol_South
				Useful_Vol_East
				Useful_Vol_West
				Rotation
				Rotation_x
				Rotation_y
				Reserved
				QNH_Datum
				terminator
				chksum
				);

##</code><code>##

if ($ident == $Idents{ Rotation_Marker }) {
   @packet{ @rotation_packet_fields } = unpack (
   $packet_template{ $ident }, $buffer);
   ...

if ($ident == $Idents{ Format_7 }) {
   @packet{ @packet_fields } = unpack (
   $packet_template{ $ident }, $buffer);

##</code><code>##

my %packet_fields = (
   $Idents{ Format_7 }	=> qw(	ident
			flags
			x
			y
			mode3
			callsign
			route
			spare1
			spare2
			flight_level
			terminator
			chksum
			),
   $Idents{ Format_7 } => qw(ident
				RDP_Ident
				Radar_Site_Ident
				site_x
				site_y
				Useful_Vol_Upper
				Useful_Vol_Lower
				Useful_Vol_North
				Useful_Vol_South
				Useful_Vol_East
				Useful_Vol_West
				Rotation
				Rotation_x
				Rotation_y
				Reserved
				QNH_Datum
				terminator
				chksum
				),
);

##</code><code>##

   @packet{$%packet_fields{ $ident} } = unpack (
   $packet_template{ $ident }, $buffer);