Erlang program to control my Onkyo receiver

iscp.erl

-module(iscp).
-author('Karl Erik Asbjørnsen <karl@asbjornsen.org>').

-define(IP, "10.0.0.222").
-define(PORT, 60128).
-define(ISCP_PREFIX, ["ISCP",0,0,0,16,0,0,0]).
-define(ISCP_MIDDLE, [1,0,0,0,"!1"]).
-define(END, 13).

-export([recv/1, start/0, m2/0]).

start() ->
    register(iscpm, spawn(iscp, m2, [])),
    register(iscphandler, spawn(iscpreceiver, start, [])),
    iscpm ! {iscp, "PWRQSTN"},
    iscpm ! {iscp, "MVLQSTN"}.

m2() ->
    {ok,Sock} = gen_tcp:connect(?IP, ?PORT, [{active,true}, binary, {packet,raw}]),
    recv(Sock).

recv(Sock) ->
    receive
        {iscp, Payload} ->
            send(Sock, Payload),
            iscp:recv(Sock);
        {tcp, Sock, Response} ->
            iscphandler ! {iscp, Response},
            iscp:recv(Sock);
        up ->
            send(Sock, "MVLUP"),
            recv(Sock);
        down ->
            send(Sock, "MVLDOWN"),
            recv(Sock);
        stopp ->
            gen_tcp:close(Sock),
            io:format("Baibai!~n");
        {tcp_error, Sock, Reason} ->
            io:format("Socket failed: ~w~n", Reason);
        {tcp_closed, Sock} ->
            io:format("Socket ~w closed [~w]~n",[Sock,self()]);
        Other ->
            io:format("Fikk ukjent melding: ~w~n", [Other]),
            recv(Sock)
    end.

send(Sock, Payload) ->
        Length = length(Payload) + 3,
        gen_tcp:send(Sock, [?ISCP_PREFIX,Length,?ISCP_MIDDLE, Payload, ?END]).

iscpreceiver.erl

-module(iscpreceiver).
-author('Karl Erik Asbjørnsen <karl@asbjornsen.org>').

-export([start/0]).
-export([receiver/1]).

start() ->
    iscpreceiver:receiver([]).

receiver(Receivers) ->
    receive
        {iscp, IscpMessage} ->
            Payload = decode(IscpMessage),
            {{Year,Month,Day},{Hour,Minute,Second}} = erlang:localtime(),
            io:format("~p.~p.~p ~p:~p:~p ~p~n", [Day, Month, Year, Hour, Minute, Second, Payload]),
            lists:foreach(fun(Pid) -> Pid ! {iscp, Payload} end, Receivers),
            iscpreceiver:receiver(Receivers);
        {register, From} ->
            io:format("Registrert ny mottaker ~w~n", [From]),
            link(From),
            iscpreceiver:receiver([From|Receivers]);
        Other -> io:format("iscpreceiver fikk ukjent melding: ~p~n", [Other])
    end.

decode(Message) ->
    IscpMessage = binary_to_list(Message),
    Payload = lists:sublist(IscpMessage, 19, sizeof(IscpMessage)-5),
    {Type, Value} = lists:split(3, Payload),
    if
        Type == "MVL" ->
            Volum = httpd_util:hexlist_to_integer(Value),
            {Type, Volum};
        true ->
            {Type, Value}
    end.

sizeof(IscpMessage) ->
    lists:nth(12, IscpMessage).