A simple Lwt server for delivering the messages to the LCD

examples/lcd_lwt.ml

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+(** An example with Adafruit character LCD, HD44780. *)
+open Gpio3
+open Lcd
+open Lwt
+
+let lcd = {
+    columns = 16;
+    rows = 2;
+    rs = GPIO20;
+    en = GPIO16;
+    d4 = GPIO19;
+    d5 = GPIO5;
+    d6 = GPIO11;
+    d7 = GPIO10;
+}
+
+(** A nicer abstraction *)
+module Cursor = struct
+  type t = { x: int; y: int; visible: bool; blink: bool; _lcd: mono_lcd }
+
+  (** Creates a new cursor at the position (0,0) *)
+  let of_lcd lcd =
+    set_position lcd 0 0;
+    { x = 0; y = 0; visible = false; blink = false; _lcd = lcd }
+
+  (** Explicitly set the position of the cursor. The arguments will be
+     taken modulo the size of the LCD. *)
+  let set_position x y cur =
+    let col = x mod cur._lcd.columns in
+    let row = y mod cur._lcd.rows in
+    set_position cur._lcd col row;
+    { cur with x = col; y = row }
+
+  (** Whether to display the cursor *)
+  let set_visible flag cur =
+    let _blinkon = if cur.blink then _lcd_blinkon else _lcd_blinkoff in
+    let _cursoron = if flag then _lcd_cursoron else _lcd_cursoroff in
+    let displayctrl = _lcd_displayon lor _cursoron lor _blinkon in
+    write8_unsafe lcd (displayctrl lor _lcd_displaycontrol);
+    { cur with visible = flag }
+
+  (** Whether the cursor is blinking *)
+  let set_blink flag cur =
+    let _blinkon = if flag then _lcd_blinkon else _lcd_blinkoff in
+    let _cursoron = if cur.visible then _lcd_cursoron else _lcd_cursoroff in
+    let displayctrl = _lcd_displayon lor _cursoron lor _blinkon in
+    write8_unsafe lcd (displayctrl lor _lcd_displaycontrol);
+    { cur with blink = flag }
+
+  (** Try writing a character, optionally with wrapping. *)
+  let write_char wrapping v cur =
+    write8 cur._lcd ~char_mode:true v;
+    let col = cur.x + 1 in
+    if not wrapping || col < cur._lcd.columns
+    then { cur with x = col }
+    else let row = cur.y + 1 in
+         let col = 0 in
+         (* set_position should do the wrapping for us *)
+         set_position col row cur
+
+  let write_bytes wrapping bts cur =
+    let f cur chr =
+      if chr = '\n'
+      then set_position 0 (cur.y + 1) cur
+      else if chr = '\r'
+      then set_position 0 cur.y cur
+      else write_char wrapping chr cur in
+    Seq.fold_left f cur (Bytes.to_seq bts)
+
+  let write_string ?(wrap=false) str cur = write_bytes wrap (Bytes.of_string str) cur
+
+end
+
+(** A useful combinator for the functions from the [Cursor] module *)
+let (|>) (m : Cursor.t) (f : Cursor.t -> 'b) = f m
+
+(** Display two lines without wrapping *)
+let display_lines l1 l2 =
+  let col_shift = 3 in
+  let maxwidth = int_of_float (float_of_int lcd.columns *. 2.5) - col_shift in
+  let trunc str =
+    let n = min maxwidth (String.length str) in
+    String.sub str 0 n
+  in
+  let open Cursor in
+  clear lcd;
+  of_lcd lcd
+  |> set_visible false
+  |> set_blink false
+  |> set_position col_shift 0 
+  |> write_string (trunc l1) ~wrap:false
+  |> set_position col_shift 1
+  |> write_string (trunc l2) ~wrap:false
+
+(** Scrolling thread *)
+
+let rec scroll lcd sleep_for : unit Lwt.t =
+  shift_left lcd;
+  Lwt_unix.sleep sleep_for >>= fun () ->
+  scroll lcd sleep_for
+
+
+(** Networking stuff *)
+
+let create_socket () =
+  let open Lwt_unix in
+  let sock = socket PF_INET SOCK_STREAM 0 in
+  (* let bind_addr = Unix.inet_addr_loopback in *)
+  gethostbyname "balthasar.local" >>= fun bind_addr ->
+  let bind_addr = bind_addr.h_addr_list.(0) in
+  bind sock @@ ADDR_INET(bind_addr, 8080) >>= fun () ->
+  listen sock 10;
+  return sock
+
+let rec handle_message ic oc () =
+  Lwt_io.read_line_opt ic >>= fun line1 ->
+  Lwt_io.read_line_opt ic >>= fun line2 ->
+  match line1,line2 with
+  | Some l1, Some l2 ->
+     Lwt_io.printl "Recieved the following message:" >>= fun () ->
+     Lwt_io.printl l1 >>= fun () ->
+     Lwt_io.printl l2 >>= fun () ->
+     Lwt.async (fun () -> Lwt_io.close oc);
+     ignore (display_lines l1 l2);
+     return ()
+  | _,_ -> return ()
+
+let handle_connection conn =
+  let fd, _ = conn in
+  let ic = Lwt_io.of_fd Lwt_io.Input fd in
+  let oc = Lwt_io.of_fd Lwt_io.Output fd in
+  Lwt.on_failure (handle_message ic oc ())
+    (fun e -> Printf.printf "Error in `handle_message': %s\n" (Printexc.to_string e));
+  return ()
+
+let create_server sock =
+  let rec serve () =
+    Lwt_unix.accept sock >>= handle_connection >>= serve
+  in serve
+
+let main () =
+  Lwt.async (fun () -> scroll lcd 0.7);
+  create_socket () >>= fun sock ->
+  create_server sock ()
+
+
+let _ =
+  setup lcd;
+  clear lcd;
+  ignore (display_lines "Hello, " "world!");
+  Lwt_main.run @@ main ()
+