How to carry out functions in a sequential manner

[espruino-discuss]

Posted at 2015-10-22 by GKeely

Hi
I'm new to Javascript/Espruino and trying to get a 4D Systems oled gmd-128 Display (serial connection) to work.
After each command is sent the display responds with an ack(0x06) if successful and next command should not be sent until ack is received.

I have managed to get the display working by using the setTimeout('func',td);
but this is not the most efficient way.

I would appreciate any info has to how to "force" sequential operation ie
Send command 1
wait for ack
Send command 2
wait for ack
etc

regards
Gerry

ps hope this makes sense !

[gfwilliams]

Posted at 2015-10-22 by @gfwilliams

Hi Gerry,

Yes - no problem! It's probably most efficient to think of it like:

• Send command 1
• When ack received, send command 2
• When ack received ....

So you might want something like this:

var ser = Serial1;
var commands = [];
var allSent = true;

function sendCommand(cmd) {
 if (allSent) { 
   // if everything was sent, start again
   Serial.write(cmd);
   allSent = false;
 } else {
  // otherwise we're sending - just push the new command onto the end
  commands.push(cmd);
 } 
}

ser.on('data', function(d) {
  for (var i in d)
    if (d[i]=="\x06") {
      if (commands.length) { 
        // send command off the start of the list
        Serial.write(commands.shift());
      } else {
        // signal we're done
        allSent = true;
      }
    }
});

Then you just call sendCommand with each command, and they get queued up.

I guess you might want some kind of timeout in there as well though?

[espruino-discuss]

Posted at 2015-10-22 by @allObjects

Is the ack something you receive serially / over RX from the module?

If so, use serial.onData(callback) with callback function receiving the ack and triggering the next command...

For use in application logic, this is of course a bit cumbersome... Therefore, you may use a FIFO with some triggering methods inbetween your app and the display which takes care of feeding the display module with the comands in a timely correct manner/sequence, where as the application just pushes to the FIFO without having to be time aware.

The FIFO is of course a buffer and could over-grow if you have a run-away in your application.

Some code 'in the rough':

var dsp =
{ cmds: [] // fifo
, idling: false
, serial: null
, exec: function(cmd) { // cmd to send to display
    this.cmds.push(cmd);
    if (this.idling) { 
      this.idling = false;
      this._tx();
    }
  }
, _tx: function() {
    this.serial.write(this.cmds.splice(0,1));
  }
, _rx: function(data) {
    if (this.cmds.length > 0) { 
      this._tx(); 
    } else { 
      this.idling = true;
    }
  }
, connect: funcrtion(serial) {
    this.serial = serial;
    this._rx.bind(this);
    this.serial.on('data',this._rx);
    this.idling = true;
    this.exec(""); // may be some initializations...
  }
}

Serial1.setup(9600); // setup Serial1
dsp.connect(Serial1);
dsp.exec("....."); // 1st cmd
dsp.exec("....."); // 2nd cmd
dsp.exec("....."); // 3rd cmd

This code has no error handling (over flow, out of synch, etc.) in place. For examples:

• .exec() needs overflow handling (some reasonable limit to the fifo size check)
• ._rx() needs check ack data received and accdingly acted on
• some state / timout has to be put in place in case communication gets 'out of sync'

A first enhancement is to leave the command in the fifo (using this.serial.write(this.cmds[0]);) until 'good' ack is received and then removed (this.cmds.splice(0,1);). If 'bad' acc is received (or timout hits), re-send/re-print or drop - with or without error logging - has to be considered.

The .connect() is currently minimal. You may extend it with additional parameter(s) - string (or array of strings) that include some display module initialization that has to be done anyway.

Can you share the code how you got your display initially working?

[espruino-discuss]

Posted at 2015-10-22 by @allObjects

@gordon, what is the reason to go for a loop in the callback, since it is serialized anyway (at best one ack for every cmd and only ack can/should trigger the next cmd)?

[espruino-discuss]

Posted at 2015-10-22 by GKeely

Hi
Thank you both for your prompt replies.

regards

Gerry

[gfwilliams]

Posted at 2015-10-23 by @gfwilliams

@allObjects true - I could just check with indexOf. I was assuming that there might be other characers sent - but if not, you could just use the occurrence of more data to trigger sending the next command.