explain the initialization sequence

_oasis

@@ -18,3 +18,18 @@ Executable "wpi-button-example"
   BuildTools:   ocamlbuild
   MainIs:       button.ml
   BuildDepends: WiringPi,unix
+
+Executable "adafruit-lcd-example"
+  Path:         examples/
+  BuildTools:   ocamlbuild
+  MainIs:       lcd_example.ml
+  BuildDepends: WiringPi,unix
+
+Executable "adafruit-lcd-server"
+  CompiledObject: native
+  Path:         examples/
+  BuildTools:   ocamlbuild
+  MainIs:       lcd_lwt.ml
+  BuildDepends: WiringPi,unix,lwt,lwt.unix,threads
+  CCLib:      -lwiringPi
+

examples/lcd.ml

@@ -0,0 +1,125 @@
+(** An example with Adafruit character LCD, HD44780. *)
+(* The documentation: https://cdn-shop.adafruit.com/datasheets/HD44780.pdf *)
+open Gpio3
+
+(** Parameters *)
+type mono_lcd = {
+    columns: int;
+    rows: int;
+    rs: pin;
+    en: pin;
+    d4: pin;
+    d5: pin;
+    d6: pin;
+    d7: pin
+}
+
+(** MAGIC NUMBERS *)
+(* Commands *)
+let _lcd_cleardisplay        = (0x01)
+let _lcd_returnhome          = (0x02)
+let _lcd_entrymodeset        = (0x04)
+let _lcd_displaycontrol      = (0x08)
+let _lcd_cursorshift         = (0x10)
+let _lcd_functionset         = (0x20)
+let _lcd_setcgramaddr        = (0x40)
+let _lcd_setddramaddr        = (0x80)
+
+(* Entry flags *)
+let _lcd_entryleft           = (0x02)
+let _lcd_entryshiftdecrement = (0x00)
+
+(* Control flags *)
+let _lcd_displayon           = (0x04)
+let _lcd_cursoron            = (0x02)
+let _lcd_cursoroff           = (0x00)
+let _lcd_blinkon             = (0x01)
+let _lcd_blinkoff            = (0x00)
+
+(* Move flags *)
+let _lcd_displaymove         = (0x08)
+let _lcd_moveright           = (0x04)
+let _lcd_moveleft            = (0x00)
+
+(* Function set flags *)
+let _lcd_4bitmode            = (0x00)
+let _lcd_2line               = (0x08)
+let _lcd_1line               = (0x00)
+let _lcd_5x8dots             = (0x00)
+
+(* Offset for up to 4 rows. *)
+let _lcd_row_offsets = [|0x00; 0x40; 0x14; 0x54|]
+
+let pulse_enable lcd =
+  digital_write lcd.en LOW;
+  (* 1 microsec pause *)
+  Unix.sleepf(0.0000001);
+  digital_write lcd.en HIGH;
+  Unix.sleepf(0.0000001);
+  digital_write lcd.en LOW;
+  Unix.sleepf(0.00001)
+
+(** write 8 bits of data *)
+let write8 lcd ?(char_mode=false) value =
+  (* one ms delay to prevent writing too quickly *)
+  Unix.sleepf(0.001);
+  let char_mode_value = if char_mode then HIGH else LOW in
+  digital_write lcd.rs char_mode_value;
+  let val_of_int i = if i > 0 then HIGH else LOW in
+  let ival = Char.code value in
+  (* write the UPPER 4 bits (in reverse order) *)
+  digital_write lcd.d4 (val_of_int ((ival lsr 4) land 1));
+  digital_write lcd.d5 (val_of_int ((ival lsr 5) land 1));
+  digital_write lcd.d6 (val_of_int ((ival lsr 6) land 1));
+  digital_write lcd.d7 (val_of_int ((ival lsr 7) land 1));
+  pulse_enable lcd;
+  (* write the LOWER 4 bits *)
+  digital_write lcd.d4 (val_of_int (ival land 1));
+  digital_write lcd.d5 (val_of_int ((ival lsr 1) land 1));
+  digital_write lcd.d6 (val_of_int ((ival lsr 2) land 1));
+  digital_write lcd.d7 (val_of_int ((ival lsr 3) land 1));
+  pulse_enable lcd
+
+(** same as [write8] but write an int (must be within the range) *)
+let write8_unsafe lcd ?(char_mode=false) ival =
+  write8 lcd ~char_mode (Char.unsafe_chr ival)
+
+let setup lcd =
+  Gpio3.setup ();
+  pin_mode lcd.rs OUT;
+  pin_mode lcd.en OUT;
+  pin_mode lcd.d4 OUT;
+  pin_mode lcd.d5 OUT;
+  pin_mode lcd.d6 OUT;
+  pin_mode lcd.d7 OUT;
+  (* send the 4-bit initialization sequence: 0011, 0011, 0011, 0010.
+     see Figure 24 in the docs. *)
+  write8_unsafe lcd 0x33;
+  write8_unsafe lcd 0x32;
+  (* set up some stuff *)
+  let displayctrl = _lcd_displayon lor _lcd_cursoroff lor _lcd_blinkoff in
+  let displayfn = _lcd_4bitmode lor _lcd_2line lor _lcd_5x8dots in
+  let displaymode = _lcd_entryleft lor _lcd_entryshiftdecrement in
+  write8_unsafe lcd (displayctrl lor _lcd_displaycontrol);
+  write8_unsafe lcd (displayfn lor _lcd_functionset);
+  write8_unsafe lcd (displaymode lor _lcd_entrymodeset);
+  Unix.sleepf(0.003)
+
+let clear lcd =
+  write8_unsafe lcd _lcd_cleardisplay;
+  Unix.sleepf(0.003)
+
+let shift_left lcd =
+  write8_unsafe lcd (_lcd_cursorshift lor _lcd_displaymove lor _lcd_moveleft)
+
+let shift_right lcd =
+  write8_unsafe lcd (_lcd_cursorshift lor _lcd_displaymove lor _lcd_moveright)
+
+let set_position lcd x y =
+  let c = x mod lcd.columns in
+  let r = y mod lcd.rows in
+  if (c < 0 || r < 0) then failwith "Lcd.set_position: Negative row or column";
+  write8_unsafe lcd (_lcd_setddramaddr lor (c + _lcd_row_offsets.(r)))
+
+let write_bytes lcd bts =
+  Bytes.iter (fun c -> write8 lcd c ~char_mode:true) bts

examples/lcd_example.ml

@@ -0,0 +1,20 @@
+(** An example with Adafruit character LCD, HD44780. *)
+open Gpio3
+open Lcd
+
+let lcd = {
+    columns = 16;
+    rows = 2;
+    rs = GPIO20;
+    en = GPIO16;
+    d4 = GPIO19;
+    d5 = GPIO5;
+    d6 = GPIO11;
+    d7 = GPIO10;
+}
+
+let _ =
+  setup lcd;
+  clear lcd;
+  set_position lcd 0 0;
+  write_bytes lcd (Bytes.of_string "Hello, world.")

examples/lcd_lwt.ml

@@ -0,0 +1,152 @@
+(** 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 ()
+