"Low level" Erlang serial interface

serctl.erl

%% Copyright (c) 2011, Michael Santos <michael.santos@gmail.com>
%% All rights reserved.
%%
%% Redistribution and use in source and binary forms, with or without
%% modification, are permitted provided that the following conditions
%% are met:
%%
%% Redistributions of source code must retain the above copyright
%% notice, this list of conditions and the following disclaimer.
%%
%% Redistributions in binary form must reproduce the above copyright
%% notice, this list of conditions and the following disclaimer in the
%% documentation and/or other materials provided with the distribution.
%%
%% Neither the name of the author nor the names of its contributors
%% may be used to endorse or promote products derived from this software
%% without specific prior written permission.
%%
%% THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
%% "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
%% LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
%% FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
%% COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
%% INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
%% BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
%% LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
%% CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
%% LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
%% ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
%% POSSIBILITY OF SUCH DAMAGE.
-module(serctl).
-include("serctl.hrl").

-export([
        open/1,
        close/1,

        read/2,
        write/2,

        tcgetattr/1,
        tcsetattr/3,

        cfsetispeed/2,
        cfsetospeed/2,

        termios/1, termios/2
    ]).
-export([
        init/0
    ]).


-on_load(on_load/0).


%%--------------------------------------------------------------------
%%% NIF Stubs
%%--------------------------------------------------------------------
init() ->
    on_load().

on_load() ->
    erlang:load_nif(progname(), []).

open(_) ->
    erlang:error(not_implemented).

close(_) ->
    erlang:error(not_implemented).

read(_,_) ->
    erlang:error(not_implemented).

write(_,_) ->
    erlang:error(not_implemented).

tcgetattr(_) ->
    erlang:error(not_implemented).

tcsetattr(_,_,_) ->
    erlang:error(not_implemented).

cfsetispeed(_,_) ->
    erlang:error(not_implemented).

cfsetospeed(_,_) ->
    erlang:error(not_implemented).


%%--------------------------------------------------------------------
%%% API
%%--------------------------------------------------------------------
termios(Attr) ->
    termios(os(), Attr).

termios(linux, <<
    Iflag:?UINT32,          % input mode flags
    Oflag:?UINT32,          % output mode flags
    Cflag:?UINT32,          % control mode flags
    Lflag:?UINT32,          % local mode flags
    Line:8,                 % line discipline
    Cc:?NCCS_LINUX/bytes,   % control characters
    Rest/binary>>) ->
    Pad = pad(1+byte_size(Cc)),
    <<
    _:Pad,
    Ispeed:?UINT32,         % input speed
    Ospeed:?UINT32          % output speed
    >> = Rest,
    #termios{
        iflag = Iflag,
        oflag = Oflag,
        cflag = Cflag,
        lflag = Lflag,
        line = Line,
        cc = Cc,
        ispeed = Ispeed,
        ospeed = Ospeed
    };
termios(bsd, <<
    Iflag:?UINT32,          % input mode flags
    Oflag:?UINT32,          % output mode flags
    Cflag:?UINT32,          % control mode flags
    Lflag:?UINT32,          % local mode flags
    Line:8,                 % line discipline
    Cc:?NCCS_BSD/bytes,     % control characters
    Rest/binary
    >>) ->
    Pad = pad(1+byte_size(Cc)),
    <<
    _:Pad,
    Ispeed:?UINT32,         % input speed
    Ospeed:?UINT32          % output speed
    >> = Rest,
    #termios{
        iflag = Iflag,
        oflag = Oflag,
        cflag = Cflag,
        lflag = Lflag,
        line = Line,
        cc = Cc,
        ispeed = Ispeed,
        ospeed = Ospeed
    };
termios(linux, #termios{
        iflag = Iflag,
        oflag = Oflag,
        cflag = Cflag,
        lflag = Lflag,
        line = Line,
        cc = Cc,
        ispeed = Ispeed,
        ospeed = Ospeed
    }) when byte_size(Cc) == ?NCCS_LINUX ->
    Pad = pad(1+?NCCS_LINUX),
    <<
    Iflag:?UINT32BE,
    Oflag:?UINT32BE,
    Cflag:?UINT32BE,
    Lflag:?UINT32BE,
    Line:8,
    Cc/bytes,
    0:Pad,
    Ispeed:?UINT32BE,
    Ospeed:?UINT32BE
    >>;
termios(bsd, #termios{
        iflag = Iflag,
        oflag = Oflag,
        cflag = Cflag,
        lflag = Lflag,
        line = Line,
        cc = Cc,
        ispeed = Ispeed,
        ospeed = Ospeed
    }) when byte_size(Cc) == ?NCCS_BSD ->
    Pad = pad(1+?NCCS_BSD),
    <<
    Iflag:?UINT32BE,
    Oflag:?UINT32BE,
    Cflag:?UINT32BE,
    Lflag:?UINT32BE,
    Line:8,
    Cc/bytes,
    0:Pad,
    Ispeed:?UINT32BE,
    Ospeed:?UINT32BE
    >>.


%%--------------------------------------------------------------------
%%% Internal functions
%%--------------------------------------------------------------------
progname() ->
    filename:join([
            filename:dirname(code:which(?MODULE)),
            "..",
            "priv",
            ?MODULE
        ]).

os() ->
    case os:type() of
        {unix, linux} -> linux;
        {unix, darwin} -> bsd;
        {unix, freebsd} -> bsd;
        {unix, netbsd} -> bsd;
        {unix, openbsd} -> bsd
    end.

% Returns pad size in *bits*
pad(N) ->
    Size = erlang:system_info({wordsize, internal}),
    (Size - (N rem Size)) * 8.