Revision as of 04:12, 29 January 2016 by Skvamme (talk | contribs) (Added info about Erlang Ports)
Jump to: navigation, search

Erlang on Raspberry Pi, starting with a fresh Raspbian image (even Lite will do). Make sure you run raspi-config to enlarge the file system to fill your memory card. Erlang takes a couple of hours to compile (when you run "make").

sudo apt-get update
sudo apt-get install wget
sudo apt-get install libssl-dev
sudo apt-get install ncurses-dev
tar -xzvf otp_src_18.2.1.tar.gz
cd otp_src_18.2.1/
sudo make install
cd ..
sudo rm -R otp_src_18.2.1/

If you don't want to install everything that comes with the standard Erlang package, you can save space and time just by putting a file with the name SKIP in every library you don't want/need in your raspberry pi. This is the applications I usually skip. Do this before you run ./configure and make.

touch lib/asn1/SKIP
touch lib/cosEvent/SKIP
touch lib/cosEventDomain/SKIP
touch lib/cosFileTransfer/SKIP
touch lib/cosNotification/SKIP
touch lib/cosProperty/SKIP
touch lib/cosTime/SKIP
touch lib/cosTransactions/SKIP
touch lib/diameter/SKIP
touch lib/eldap/SKIP
touch lib/ic/SKIP
touch lib/gs/SKIP
touch lib/megaco/SKIP
touch lib/orber/SKIP
touch lib/ose/SKIP
touch lib/otp_mibs/SKIP
touch lib/parsetools/SKIP
touch lib/percept/SKIP
touch lib/reltool/SKIP
touch lib/snmp/SKIP
touch lib/test_server/SKIP
touch lib/typer/SKIP
touch lib/webtool/SKIP
touch lib/wx/SKIP
touch lib/xmerl/SKIP

You start the interactive shell with erl and quit with Ctrl-g q. Read about Erlang at [1].



There is a very nice graphics library written in Erlang. It makes a perfect match if your application is written in Erlang and you are using a small screen where you don't want a window manager. The screen in the image is an Adafruit 5" Touchscreen 800x480. Erlang ex11 is writing directly to the screen (X11 server). Experience soft realtime graphics. Read about it here [2]

To help create new widgets there is a small program included to convert DXF-files to erlang ex11 drawing primitives. Download or draw your own graphics in a CAD system and save as DXF. Convert the DXF file with dxf2erl:start("filename.dxf"). from the erlang console.

The DXF file can be created in QCAD (free) [3] , AUTOCAD, Google Sketchup Pro and other CAD systems. Entities with higher thickness will be drawn last. Closed polylines will be filled areas in ex11.


Erlang is using ports to communicate with all the different hardware that you are connecting to you Raspberry Pi. In the image to the right I am using an ex11 line diagram widget to show the load on my mains meter in the basement. The Erlang Port I'm using is programmable in the language Forth, read more about it Forth The fact that it is programmable makes it possible to read multiple sensors and command multiple actuators simultaneously and it is even possible to programmatically re-program the port from a running Erlang application.


This is a simple owserver client. It can call dir and print a directory listing from a onewire network. First, you have to install owfs:

sudo apt-get install owfs

Configure owfs in /etc/owfs.conf

Then, save a file, onewire.erl with the following content:


start() -> spawn_link(?MODULE,init,[]).

init() ->
	io:format("New process: ~p~n", [?MODULE]),
	{ok,Socket} = gen_tcp:connect("localhost", 4304, [binary, {packet, 0}]),
	Version = 0,
	Type = 10,
	Control_flags = 36,
	Size = 1024,
	Offset = 0,
	Raw = <<"/",0>>,
	Payload = size(Raw),
	ok = gen_tcp:send(Socket,<<Version:32,Payload:32,Type:32,Control_flags:32,Size:32,Offset:32,Raw/binary>>),

loop(Socket) ->
		{tcp,Socket,Bin} -> Dir = get_directory(Bin),
			io:format("In ~p: Dir is: ~p~n",[?MODULE,Dir]),
		{ow_dir,Raw,Pid} -> 
			Version = 0,
			Type = 10, % get
			Control_flags = 36,
			Size = 1024,
			Offset = 0,
			Payload = size(Raw),
			ok = gen_tcp:send(Socket,<<Version:32,Payload:32,Type:32,Control_flags:32,Size:32,Offset:32,Raw/binary>>),
			receive {tcp,Socket,Bin} -> Dir = get_directory(Bin), Pid ! {ow_dir,Dir} after 10000 -> ok end,
		{tcp_closed,_} -> ok;
		Any -> io:format("~p got unknown msg: ~p~n",[?MODULE, Any]),

% Function get_directory(Bin)
get_directory(Bin) ->
get_dir(<<>>,Dir) -> Dir;
get_dir(<<0,0,0,0,0,0,0,0, Return_value:32/signed-integer,Rest/binary>>,_Dir) when Return_value /= 0 -> 
	io:format("Return value is: ~p and Rest is: ~p~n",[Return_value,Rest]);
get_dir(<<_Version:32,_Payload:32,0:32,_Control_flags:32,Size:32,_Offset:32,Raw:Size/binary,0,Rest/binary>>,Dir) ->
get_dir(<<_Version:32,Payload:32,Return_value:32,_Control_flags:32,_Size:32,_Offset:32,Raw:Payload/binary>>,Dir) ->
	io:format("Return value is: ~p and Raw is: ~p~n",[Return_value,Raw]),

Compile the file with: erlc onewire.erl Start an Erlang console with erl and type onewire:start(), and you should see a listing of your onewire network.

Another Erlang module can send this message to onewire: {ow_dir,<<"/",0>>,self()} and get back a directory listing.