Issue communicating over serial to Arduino from Matlab

Question

Update 2: Turns out adding a pause(2) after opening the serial port was all it needed.

Update: I am able to manually enter the Matlab code into the Matlab command window and it will update the LEDs as expected, but I cannot call my function that does so. I will try adding time delays, perhaps the Arduino buffer cannot keep up.

I am using an Arduino Uno with the Sparkfun PWM shield to control 3 LEDs. I have written an Arduino sketch that looks for serial input to set the LED values, and Matlab code that prepares and sends the serial output. See all the code below.

For some reason this code, which was working several months ago, has stopped working. I am using 2011b version of Matlab now, and was using 2013a before. Nothing else has changed.

I believe the issue is with the serial communication, as I can get it to work by having Matlab and Arduino IDE running at the same time, opening the serial monitor in Arduino IDE, then issuing the Matlab command. It sets the LED values as desired. In order to send another command I need to first close, and re-open the Arduino serial monitor.

Matlab code:

function [] = displayColor(RGB)

s1 = serial('/dev/tty.usbmodem1411','BaudRate',9600);

fopen(s1)

messageRed = bitshift(1,12)+RGB(1);
messageGreen = bitshift(2,12)+RGB(2);
messageBlue = bitshift(3,12)+RGB(3);
fwrite(s1,messageRed,'uint16','sync');
fwrite(s1,messageGreen,'uint16','sync');
fwrite(s1,messageBlue,'uint16','sync');
updateMessage = 0;
fwrite(s1,updateMessage,'uint16','sync');

fclose(s1)

end

Arduino code:

#include "Tlc9540.h"
int newVal = 0;

void setup(){
Tlc.init();
Serial.begin(9600);
delay(1000);
}

void loop(){

updateChannel();  

}

int updateChannel()
{

int B;
int code;
int value;

  if (Serial.available())
  {
    //Read First Byte
    B = Serial.read();
    //Blocking - waiting for second byte
    while (!Serial.available()){}
    B+=Serial.read()<<8;
    code = (B&(B1111<<12))>>12;
    value = B&4095;
    switch (code)
    {
      case 0:
        Tlc.update();
        break;
      case 1:
        Tlc.set(0,value);
        Serial.print(Tlc.get(0));
        break;
      case 2:
        Tlc.set(1,value);
        Serial.print(Tlc.get(1));
        break;
      case 3:
        Tlc.set(2,value);
        Serial.print(Tlc.get(2));
        break;
    }
  }  
}

Answer 1

In order to engage the Arduino over the serial port through Matlab it seems to need a time delay of ~2 seconds. Adding a delay before starting to send data over the serial line did the trick.

Answer 2

I solved that problem by setting my own serial terminator (I used ! as terminator). And when I send a serial command, I use ! as terminator.

set(arduino,'Terminator','!'); % setting my terminator

then in my code:

test_free = 'mode=free,axis=1,dir=1,speed=50,pos=13245!';
fprintf(arduino,test_free);

I think that the problem is that matlab is waiting for a terminator. Than if there's not fullfilling, timeout is executed and set to 2sec. That's why execution is possible after a delay bigger than timeout.